42 NO VEMBER/DECEMBER 2001 WINEGR OWING

ative. The same can be said of a plant's water potential. For example, when more water is Irrigation lost from a leaf via transpiration than moves into the leaf from the vascular tissue, its water potential will become more negative due to a relative increase in its solute concentration. of w i rapes This is important as water in plants and soils moves from regions where water potential is relatively high to regions where water potential is rela- tively low. Such differences in water in potential will result in movement of water from cell to cell within a plant or from regions within the soil profile that Cal Lorry E. WIIIIams y.t portion of the growing season in contain more moisture to those with Department of Viticulture Enology these areas and vineyard water use less. University of California-Qavis, and can be greater than the soil's water One way to measure the water Kearney Agricultural Center reservoir after the winter rainfall, potential of a plant organ in the field supplemental irrigation of vineyards (such as a leaf) is by using a pressure SYNOPSIS: How much irrigation water is may be required at some point dur- chamber. required to grow quality winegrapes ing summer months. The leaf's petiole is cut and the leaf depends upon site, the stage of vine quickly placed into the chamber with growth, row spacing, size of the vine's IRRIGATION MANAGEMENT the cut end of the petiole protruding canopy, and amount of rainfall occur- No matter where grapevines are out of the chamber. Once the leaf is ring during the growing season. Below, grown, two major questions concern- growers are presented with means to ing vineyard irrigation management determine when irrigations should must be answered: 1) When to start? commence and to calculate full vine and 2) How much water to apply? water use based on the results of 10 years of field trials in California wine- When to start irrigating grape growing regions. Implications .1;7' Deciding when to begin irrigating for such information to assist in vine- can be determined several ways. Soil- yard irrigation management are based tools such as a neutron probe included. and capacitance sensors can determine the actual or relative amounts of water oastal, winegrape production in the rooting zone of grapevines. areas in California are character- Plant-based tools, such as a pressure ized by warm days and cool chamber, can be used to measure vine nights, although high tempera- water status. turesc (104Q to 1162F) may occur for a Regardless of the method, a "value" few days each growing season. Some is determined which indicates that the areas may have fog lasting late into the vines may need water. Once this value morning. is reached, an irrigation event should Rainfall is greater in northem,coastal occur. valleys and diminishes as one travels south. In coastal valleys, evaporative Using a pressure chamber demand can range from 35 to 50 inches Water has free energy, a capacity to of water throughout the growing sea- do work. In plants, water's free energy son (between budbreak and the end of (or chemical potential) is usually October). referred to as "water potential." Pure Many of the soils in the coastal water will have a water potential of production areas are clay loam to 0 bars (bar is the unit of measurement). clay-type soils, which at field capac- Any solute (such as sugars, mineral ity, generally hold more water than ions, and amino acids) added to water sandy-type soils. Since the majority Randell Johnson (Hess Collection Winery, will lower its water potential, i.e. the Napa, CA) uses pressure chamber. (Photos of rainfall occurs during the dormant water potential will become more neg- by Richard Camera.) 201 NOVEMBER/DECEMBER 2001 mew- .i41,3%:4; rFW-0.1 254 WINEGROWING

77,71 aSe

removed from the plant, the tension in deficits than those given greater those that were not bagged (the latter the petiole's xylem is released and the amounts of water.' Thus, leaf water being more negative). sap withdraws from the cut surface potential can be used to estimate the The bagged, leaf is. placed inside the and moves into the blade. water status of a plant. Units of water chamber with the petiole sticking out As the chamber is pressurized, the potential are expressed in bars, as men- (see photo)..-Theiiime from enclosing water potential of the leaf is raised by tioned above, or megapascals (MPa) the leaf inside the plastic bag to placing the amount of pressure applied so that (1.0 MPa =10 bars). it inside the chamber should be 10 sec- at the balance pressure (the pressure In all of my irrigation trials, I have onds or less-:.The chamber is pressur- required to force the sap to the surface measured leaf water potential to ized with compressed nitrogen until of the cut end of the petiole), the water assess vine water status. I usually the sap just exudes from the cut end of potential is zero. The original leaf measure midday leaf water potential the petiole. If the sap forms into a lens water potential plus the balance pres- between 12:30 and 1:30 PM. I select or hemisphere, then the sample, has sure equals zero. Therefore, the nega- mature, fully expanded leaves been over-pressurized. • tive of the balance pressure equals the exposed to direct sunlight (no shading The recommended rate , of pressur- original leaf water potential. on the leaf). I have found that any ization is leSS- than 1 bar 1>er -second A more complete explanation of the fully expanded leaf on the outside of initially, then slowed to less than 0.2 pressure chamber technique, theory, the canopy will be appropriate as long bar per second as"the balanCing pres- .-possible errors, and problems can be as it is not senescent (starting to turn sure is approached.' - The end point found in "Measurements of plant yellow), diseased, or suffering from should be observed with a magnifying water status," Hsiao.2 insect damage. lens and adequate light. The water potential of a plant leaf The leaf blade is enclosed inside a While the above description of the will be greatest at pre-dawn, then plastic bag (plastic sandwich bags are pressure chamber involves use of -com- decline (become more negative) during satisfactory) and then the petiole is cut pressed nitrogen, a new chamber has the day to reach a daily minimum, then with a sharp razor blade. The plastic been developed that doesn't require increase as the sun sets. This type of bag enclosing the leaf blade is to mini- compressed gas cylinders. This cham- pattern will occur regardless of the mize transpiration between petiole ber is pressurized via a manual pump availability of water in the soil profile. excision and pressurization within the and is very portable. However, pre-dawn and midday chamber. I have found a difference in Water potential values obtained by minimum values will be more negative leaf water potential of 2 to 3 bars using this technique can be dependent for plants experiencing soil moisture between bagged grape leaves and upon ambient vapor pressure deficit (VPD), which increases as relative humidity decreases; temperature and light, because all of these contribute to evaporative demand; time of day the measurement is made; and the amount of water in the soil profile. Since, time of day is very important, and the evaporative demand will vary considerably throughout the day, I limit taking leaf water potential mea- surements to one-half hour on either side of solar noon. That is when a grapevine uses the greatest amount of water on a daily basis.' I have found that midday leaf water potential values of fully irrigated vines on a day of low evaporative demand (ambient temperature at the time of measurement 85 2F) will be approxi- mately 1 bar higher (less negative) than on a day when ambient temperature is 982F at the time of measurement. This is also true for vines that are deficit- irrigated. One can also assess vine water sta- The petiole should be carefully observed in order to capture the measurement when the sap tus by taking water potential readings just exudes from the cut end. prior to sunrise (pre-dawnZoS leaf water potential) or by measuring stem water made one-half hour on either side of The information needed to sched- potential at midday. solar noon, that is 1 FM PDT. ule irrigations at daily, weekly, or Stem water potential is deter- In my current irrigation experi- other intervals throughout the grow- mined by enclosing a leaf in a plas- ments, I generally do not initiate the ing season includes potential evapo- tic bag surrounded by aluminum application of water until midday leaf transpiration (ET0) and reliable crop foil, at least 90 minutes prior to water potential is at or more negative coefficients (k c). Potential ET (also when readings are to be made. This than -10 bars. known as reference ET) is the water procedure eliminates transpiration At present, many growers and vine- used per unit time by a short green and the leaf water potential will yard consultants do not begin irrigation crop completely shading the ground. come into equilibrium with the of white wine cultivars until a midday leaf water potential value of -10 bars has Ideally, the crop is of uniform height water potential of the stem (i.e. stem and never water-stressed. water potential). been reached or a -12 bar value for red A recent study on almond trees has wine cultivars. The date during the grow- ing season these values are obtained is Potential ET (ET0) shown that water potential values ET, is a measure of the evaporative measured on shaded leaves (covered dependent upon rooting depth of the vines, soil texture, soil moisture content, demand of a particular geographic with a damp cloth just before leaf exci- region throughout the year. Current (or sion) are very similar to values of stem vine canopy size, row spacing, trellis type, and evaporative demand. near-real time) ET° data are available water potential.' from the California Irrigation Manage- I have compared leaf water poten- For example, in 2001, leaf water potential of Thompson Seedless grape- ment Information System (CIMIS) tial of leaves under naturally occurring which is operated by the California shade with stem water potential values vines at the Kearney Ag Center did not reach -10 bars until bloom (the first week Department of Water Resources. of grapevines this past summer and of May), at which time irrigations began. There are more than 90 weather sta- found the two are very similar in some In a Cabernet Sauvignon trial near tions located around the state where instances. In other instances they were Oakville in 2001, irrigation was not ini- environmental data are collected to cal- not. culate ETo. I believe the 'discrepancy is due to tiated in a trellis and irrigation study Environmental variables measured the fact that on some trellis systems until a midday leaf water potential to calculate ET, are mean, hourly (such as the VSP), it is difficult to find value of -11 bars was measured. solar radiation, air temperature, leaves that are completely shaded (no Accordingly, irrigation was initiated on vapor pressure, and wind speed. sunflecks present on individual leaves) June 3, June 11, and July 10 for a VSP These variables are then used to cal- or in deep enough shade that transpi- trellis (1m X lm planting), a Wye (or culate other variables such as net ration truly is minimal. lyre) trellis with 9-ft. row spacing, and radiation and vapor pressure deficit Some researchers feel that stem a VSP trellis with 9-ft. row spacing, which are then inserted into an equa- water potential is a better %measure of respectively. tion to calculate ET0.4 vine water status than leaf water Since soil type and rooting depth potential since it somewhat minimizes were the same for all trellises in the Potential ET may also be obtained the effects of the environment on an trial near Oakville, the differences in from weather stations operated by exposed leaf as outlined above. the date irrigations began (i.e. when other entities (such as stations oper- However, Dr. Merilark Padgett- leaf water potential reached -11.0 bars ated by the Paso Robles Vintners & Johnson and I have demonstrated at midday) were due to the differing Growers Association in the Paso (unpublished data) that pre-dawn amounts of water used by each. Hence Robles region). leaf, midday leaf, and midday stem the rate water was depleted from the Potential ET will vary seasonally water potential of Vitis vinifera culti- soil profile. and is low at the beginning of the vars and different season, highest in mid-summer, and Vitis spp. are all then decreasing thereafter. Between highly correlated with one another How much water to apply I have spent the last 10 years deter- budbreak and the end of October, and with other measures of vine water ET, can range from 35 to 50 inches of status. Based on these findings, mid- mining irrigation requirements for raisin, table grape, and wine grape water in the coastal valleys of day leaf water potential is an appro- priate and convenient means of esti- vineyards in all major grape-growing California. mating vine water status, however, regions of California. For example, ET, from March one must follow precisely the tech- Regardless of grape type, in my through October in 1997 for the niques outlined above. opinion, once the decision to begin Cameros region of Napa Valley, Green- It is interesting to note that D.A. irrigations is made, vine water ' field in the Salinas Valley, Paso Robles, Goldhamer and E. Fereres found that a requirements are dependent upon and Fresno were 44, 44, 51, and 48 major source of variation in determining evaporative demand at the location of inches, respectively. tree water status (stem and shaded leaf the vineyard, stage of vine develop- Historical ET0 in the Santa Maria water potential) is due to operator error.' ment, and percent ground cover by region for the above-mentioned Thus, whoever is taking your vine water the vine's canopy. This is because the months is estimated to be 36 inches. status measurements, amount of water depleted from the Therefore, if identical vineyards (same whether midday spacing, leaf or stem water potentials, should be soil profile has been significantly cultivar, trellis system, row cognizant of possible errors associated reduced by that time (especially if no canopy size, etc.) were growing at all with their technique. water had been applied from the time five locations, then seasonal vine water My research indicates that the mid- of budbreak to that point) and the use would be lowest in Santa Maria day leaf water potential of vines that are majority of the water a vine subse- and highest in Paso Robles. The differ- irrigated at 100% of water use is gener- quently will use is dependent upon ences would be due to varying evapo- ally never more negative than -10 bars what is applied. rative demand at those locations. (equivalent to a stem water potential value of -7.5 bars).' Measurements are There are several reasons why Crop coefficients they use 2 mm of water (slightly more The next piece of information than two gallons) and are therefore grapevine water use and the crop needed to determine vineyard water assumed not to be under water stress. coefficients may be related to the use is seasonal crop coefficients (k,). Water use of the vines in the percentage of shaded area when mea- The k, is the fraction of water a non- lysimeter, between budbreak and the sured at midday: water-stressed crop uses in relation to end of October, from four years after 1) The driving force of ET, net radia- tion, is greatest between 11 Am and that of ET,: planting until the present, has ranged k, = ET, + ET, from 29 to 34 inches (approximately 2 Pm. where ET, is crop ET. The k, is 1,400 to 1,700 gallons per vine). 6 2) Approximately 75% of the daily dependent upon the stage of vine Potential ET at the same location over water use by vines growing in the growth, degree of ground cover the same years has ranged from 42 to lysimeter occurs between 10 AM and (shading), height, and canopy resis- 47 inches. Daily water use of vines 2 PM. tance (regulation by the vine or crop). growing within the lysimeter will 3) The shade beneath a vine is an indi- The k, will vary throughout the average 10 to 12 gallons at maximum rect measure of how much solar radia- growing season; it is not a constant canopy, mid-summer. tion the vine is intercepting. fraction of ET°. It is low early on and During the 1998 and 1999 growing 4) The shade beneath the vines varies then as the canopy develops, it will seasons, a study was conducted to only slightly between 9 AM and 3 PM for increase (Table I). determine the relationship between east/west rows (row direction in the In the past, seasonal crop coeffi- leaf area of the vines in the lysimeter, lysimeter vineyard). cients have been developed for vine- shaded area cast on the ground at solar 5) As the season progresses, the vine's yards in the San Joaquin Valley. noon, and grapevine water use. Thus, canopy gets larger, resulting in more Unfortunately, when these seasonal leaf area was estimated and shaded light being intercepted (more shaded crop coefficients were utilized in area on the ground was determined at area on the ground) and greater water coastal valley vineyards, they did not various times throughout the growing use. work very well. season. Various means of adapting these The study found that, at full canopy, Impact of trellis and row spacing crop coefficients to different trellises shaded area on the ground comprised There are numerous trellis systems and row spacings have included the use approximately 50% of the total land used for winegrape production in of another coefficient (canopy coeffi- area allocated per vine within the vine- California today. There are systems in cient) that is a function of canopy size. yard. which little management is used In order to develop crop coeffi- In 1999, the shoots of the two vines (sprawl systems) and those, which cients, one must be able to measure or growing within the lysimeter were are highly manipulated. The latter estimate grapevine water use through- allowed to grow across the row mid- systems include the VSP (vertical out the growing season. With the aid of dles on either side of the lysimeter. The shoot positioned trellis) and vertically a weighing lysimeter, I have deter- shaded ground area just prior to that , divided canopies such as the Scott mined seasonal crop coefficients for time was about 60%. A support system Henry or Smart/Dyson trellises. Thompson Seedless grapevines grown was then constructed to raise the Horizontally divided canopy trellis at the University of California's shoots (simulating an overhead trellis systems include the lyre, U and Wye Kearney Agricultural Center.'' system) and the percent ground cover trellises, and the GDC (Geneva A weighing lysimeter is a sensitive increased to approximately 75%. Double Curtain). piece of equipment that is able to mea- Actual vine water use prior to raising Any of the above winegrape trellis sure ET of plants on an hourly, daily, the canopy was 12.7 gallons per day, systems that increase the percent and seasonal basis. and after raising the canopy, it increased ground cover should also increase The lysimeter at the Kearney Ag to 16.7 gallons per day. This indicates vineyard irrigation requirements Center is comprised of a large soil that it was the orientation of the canopy based upon observations using container (2m wide, 4m long, and 2m (determined by the trellis system) and Thompson Seedless grapevines in the deep) that sits upon a scale. The soil not the total leaf area per vine that dic- lysimeter. surface of the container is at the same tated how much water the vine used, if In addition, as the tractor-row width level as the soil level of the vineyard the vine was not water-stressed. decreases, the percent ground cover or surrounding it. Therefore, the soil It was also found that vine water shaded area will increase. One would container and scale are below use (ET,) and the crop coefficient therefore assume that vineyard water ground. were linear functions of the amount of use would increase as the distance Two grapevines were planted in the shade measured beneath the vines at between rows decreased. lysimeter in 1986. Vines were also solar noon. The equation to describe I have independently developed planted around the lysimeter with vine the relationship between the crop crop coefficients for two different train- and row spacings of approximately 7V2 coefficient (1

Table III - Calculated water use of Cabernet Sauvignon Table V - Relative yield as a function of applied irrigation amounts grapevines in Paso Robles during the 2000-growing season. (fraction of estimated full ET) at four locations and two cultivars, ) was obtained from the Paso Robles Potential ET (ET0 Cabernet Sauvignon and Chardonnay. All vineyards used a VSP trellis. Vintners and Growers Association's PR1 weather station. Values at each location are the mean of three different rootstocks except Row spacing was 10 ft. and vine spacing was 6 ft. (726 vines per acre). at Paso Robles, which had five rootstocks, with data collected for a It was assumed that there were 27,500 gallons per acre-inch. minimum of three growing seasons. ET ETc Irrigation Treatment (fraction of estimated ET C) Month Week ET. (in.) lc ETc (in.) (gal./acre) (gal. /vine) Rain (in.) Location Cultivar 0.25 0.5 0.75 1.0 1.25 May . 1 1.38 0.14 0.19 5,225 7.2 0 - (percent of maximum weight)* - 8 1.38 0.17 0.23 6,325 8.7 0 Oakville Cabernet 77 96 100 99 99 15 1.50 0.18 0.27 7,425 10.2 0 Paso Robles Cabernet 61 70 81 91 100 ** 22 1.69 0.22 0.37 10,175 14.0 0 Gonzales Chardonnay 65 81 87 89 100 29 1.89 0.25 0.47 12,925 17.8 0 Edna Valley Chardonnay 92 90 92 98 100 June 5 1.61 0.28 0.45 12,375 17.0 0.2 12 1.73 0.32 0.55 15,125 20.8 0 " The weights of each treatment were divided by the treatment with the greatest weight. 19 1.69 0.36 0.61 16,775 23.1 0 The treatment with the greatest weight was set to 100%. 26 1.97 0.39 0.77 21,175 29.0 0 July 3 1.57 0.41 0.64 17,600 24.2 0 10 1.61 0.43 0.69 18,975 26.1 0 17 1.97 0.44 0.87 21,450 29.5 0 *4* 24 2.05 0.44 0.90 24,750 34.1 0 31 2.05 0.45 0.92 25,300 34.8 0 August 7 1.89 0.46 0.87 23,925 33.0 0 Table VI - Relative pruning weight as a function of applied irrigation 14 2.05 0.47 0.97 26,675 36.7 0 amounts (fraction of estimated full ED at four locations and two 21 1.73 0.48 0.83 22,825 31.4 0 cultivars, Cabernet Sauvignon and Chardonnay. All vineyards used a 28 1.26 0.49 0.62 17,050 23.5 0 VSP trellis. Values at each location are the mean of three different rootstocks except at Paso Robles, which had five rootstocks, with data *, **, and *** denote dates of the initiation of irrigation, approximate date of bloom, and approximate date of veraison, respectively. Vines were harvested September 27, 2000. collected for a minimum of three growing seasons.

Irrigation Treatment (fraction of estimated ET,) Table IV - Relative berry weight as a function of applied irrigation Location Cultivar 0.25 0.5 0.75 1.0 1.25 amounts (fraction of estimated full ET) at four locations and two - (percent of maximum weight)* - cultivars, Cabernet Sauvignon and Chardonnay. All vineyards used a Oakville Cabernet 85 89 100 96 99 VSP trellis. Values at each location are the mean of three different Paso Robles Cabernet 61 67 79 88 100 rootstocks except at Paso Robles, which had five rootstocks, with data Gonzales Chardonnay 75 81 87 96 100 collected for a minimum of three growing seasons. Edna Valley Chardonnay 87 87 92 98 100 * The weights of each treatment were divided by the treatment with the greatest weight. Irrigation Treatment (fraction of estimated ETc) The treatment with the greatest weight was set to 100%. Location Cultivar 0.25 0.5 0.75 1.0 1.25 - (percent of maximum weight)* - Oakville Cabernet 83 93 98 100 98 Paso Robles Cabernet 78 88 95 98 100 Gonzales Chardonnay 77 89 96 98 100 Edna Valley Chardonnay 82 89 97 99 100

* The weights of each treatment were divided by the treatment with the greatest weight. V The treatment with the greatest weight was set to 100%. OWINI° 4111.6 21 I II MARCH/APRIL 2005

Abscission (yellowing and dropping) of basal leaves is an indication of excessive water stress and should generally be avoided.

given that irrigation is such a funda- mental aspect of viticulture, it is more appropriately discussed in its entirety, which I will endeavor to do here. Integrated irrigation management may be thought of as an interaction of three elements: A. Irrigation scheduling, B. Water status monitoring and, C. Irrigation strategy. All three components are required for proper wine grape irrigation, and MONITORING AND SCHEDULING all will be discussed in this article. Integrated irrigation Irrigation Management of California winegrapes Scheduling Monitoring

III Mark Greenspan, Ph.D., rainfall in Bordeaux is often perfect for Viticulture research manager maintaining vineyards without sup- Gallo of Sonoma, Healdsburg, CA plemental irrigation, most California Strategy vineyards require irrigation to carry oes dry farming produce superior them through the growing season. wine? Not always. We are fortu- Fortunately, California is blessed with A. IRRIGATION SCHEDUUNG nate in California to enjoy condi- enough rain during the wet season to Irrigation scheduling is simply the tions that are undoubtedly allow capture and storage for irrigation practice of deciding how much irriga- amongp the best in the world for growing during the thy season. tion to apply, how often. Blunders in wine grapes. Water resources are abun- In many ways, that is a distinct bene- irrigation scheduling can be made in dant to maintain vineyards throughout fit to California, as we are not beholden several fundamental ways, including the season, even with a nearly complete to weather patterns that influence the irrigating only on specific days of the lack of summer rainfall. growth of vine canopies or development week, cutting off irrigation during cool Despite living in a climate of seasonal or quality of our fruit crop. While irriga- or cloudy weather, or by waiting for aridity, we all too often attempt to mimic tion is not required in some vineyard the vineyard to show signs of stress the Old World style of grape growing sites, due to a high water table or before pouring on a lake of water. without supplemental irrigation. extremely deep and fertile soils, dry Scheduling of irrigation should be However, it is critical to remember farming is essentially a misnomer, since performed consistently and, to some that California's rainfall pattern differs non-irrigated vineyards that have an extent, independently of vineyard tremendously from Europe's. For ample natural water supply are any- moisture stress symptoms (see Section instance, Bordeaux receives almost 33 thing but dry! B). Stress symptoms should be used to inches of annual rainfall, distributed I have found, through experimenta- modify irrigation schedules, not to almost uniformly throughout the year tion and trial-and-error, that judi- determine actual irrigation applications. (Figure I). In contrast, St. Helena in ciously irrigated grapevines can pro- Napa Valley totals almost 35 inches — duce intensely flavored and rich wines When to start irrigation most all of it falling over a six- to that are sought after by those operating Irrigation scheduling cannot begin seven-month period!'s "old-style" dry-farmed vineyards. until a specific starting date has been St. Helena, like much of California, Irrigation articles often focus on one determined each season. Generally receives essentially no rainfall from or two aspects of the topic, such as speaking, for regions that receive a suf- June through September. While the using ET or pressure "bombs." But ficient amount (roughly 8 to 10 inches) 212 but itisanacceptable secondchoice. error thanusingthepressure chamber, method willtakeabitmore trialand chamber inordertodeterminetheirriga- slows downand,eventually, stops. This related tomid-dayleafwaterpotential tion triggerShootelongationishighlycor- absolutely necessarytohaveapressure a pressurechamber.Fortunately,itisnot additional shootelongationisdesired. become apparentwhenshoot elongation in lessvigorousblocks,forwhichsome 'seri The-8barendmightalsobechosen season. Formostredvarieties,-10barsis sheet tographtheshootlengths, itwill are morepronetowaterstressduringthe end isusedforwhitegrapesorblocksthat potential reaches-8to-10bars.Thebar shoot lengthsweekly.Byusing aspread- irrigation seasonwhenmid-dayleafwater is themostusefultoolforthispurpose. Section B[page311). potential withapressurechamber(see each vineyardblockandmeasurethe This providesanopportunitytodetermine They include: the pointofinitiationatverylowcost. leaf waterpotentialofabout-9to-10bar the triggerforirrigationinitiation. • (Figure II).Elongationceasesatamid-day • • crop. Thelatterfactorwillhaveatreme ity; andpresenceorabsenceofcov precipitation; soilwater-holdingcapa profile isfilledtofieldcapacitybywint reached willdependonnumerousfa controlled. Exactlywhenthatstate from thesoilsothattheirgrowthcan1 early on. extent, allowingforrapidvinegrow break to"fill"thesoilprofileson grass cropismaintained. the spring,especiallyifatallperenni dous influenceonwaterdepletionrate tors, includingwhetherornotthesr the vineshaveextractedsufficientwat irrigation schedulinginthespringun monly appliedpriortothetimeofbu large irrigationapplicationiscor from theprofile.Inmorearidregions amount ofwaterhasbeenextract tiling irrigationuntilasufficie spring, wedonotwishtobeginsche the soilprofiletofieldcapacitybyear of dormantseasonprecipitationtoI Some growersdonotwishtoinvestin A goodruleofthumbistobeginthe I havefoundthatthepressurechamber Measuring mid-dayleafwater Monitoring shootelongationrate,and Monitoring soilmoisture, There areseveralwaystodetermine Mark outabout10shootsthroughout However, itisnotadvisabletobeg irrigation, orRDI).Thiswill bedis- can beagoodthing(regulated deficit vines. Mindyou,a creates excessivewaterstress inthe growth, andtoolittlewater in thesoil amounts resultsinexcessive vine water availabilityinluxurious draw it. while alsobeingcarefulnottoover- too muchinthe(lowinterest)account, matrix, andwewanttomanagethe chamber asaprimarytool,themost excessive irrigationisapplied. growing, theywillrarelyrestartunless continued growth.Onceshootsstop that irrigationbeinitiatedtoallowfor shoots or20to22nodes),itisimperative sufficient length(aboutfour-foot-long down beforetheshootshaveattained shoot length.Ifelongationslows elongation "cash" flowsuchthatwedon'tkeep gation). Thebankisactuallythesoil amount thatisbeingdeposited(byirri- to monitorhowmuchisbeingwith- drawn (bythevines)against a checkingaccount.Viticulturistsneed How muchwatertoapply? critical decisionpoint chamber datatogethertoarriveatthis shoot lengthmeasurement,andpressure intelligent methodistousesoilmoisture, The analogytograpevinesisthat While Isuggestusingthepressure Be carefultolooknotonlyatshoot Irrigation schedulingislikehaving year averagesfromeachregion. Figure I:RainfalldistributioncomparisonbetweenBordeauxandSt.Helena.Dataare30- Monthly Precipitation (inches)

A, 0 ■1 iS2 CAI •Ikto cr, ...4 co rate, <,..r. • but alsoattheactual little 40 , water stress MI1 --*--Bordeaux -32.7annualinches -111-St. Helena-34.9annualinches 10 PWV). soil reserve. deposits andwithdrawalsintoour cussed inSectionC(May/June2005 cation interms of hours,sincethatishow erally easiestto expressirrigationappli- and forthfrominches.However, itisgen- use theaboveequationstoconvert back tracking. Inthatcase,wewould needto the bestmethodofirrigation application using aninlineflow-meter,is probably inches = or, fromhourstoinches: hours = ful units: we needtoconvertthemmoreuse- are usuallyexpressedindepthunits, application. Sinceconsumptivevalues volume. Itismoreconvenientto in inchesofdepthoracre-inches equivalent towithdrawalunits.Tradi- eral differentways.Theimportant irrigation appliedtoavineyardinsev- 1 acre-inch=27,154gallons terms ofgallonsperacreorhours express dripirrigationamountsin tionally, irrigationvolumeisexpressed thing istohavetheapplicationunits Measuring waterapplication Measurement ofgallonsapplied, To convertfrominchestohours: We canaccountfortheamountof emitter rate(gph) x emitterspervinevinesacre 1... But first,let'sdiscussthe hours x 5t 4 x inches x vines peracre °1 21'S emitter rate(gph) 27,154 0 44 x .06 27,154 emitters pervine ‘, 0

. 0 6 .0 e s.. s (3) (2) (1)

index, like the Dow Jones Industrial Average and S&P500 are to the stock market. We can raise or lower a second fudge factor (the management coeffi- cient) in reaction to -observations of vineyard water status (Section B) to compensate for errors and for vineyard management strategy. Whatever model you use for K,, stick with it year after year. Previously-pub- lished crop coefficients for grapes were determined for rather bushy California sprawl vineyards in the Central Valley and are, therefore, too high for the thriftier winegrape canopies that cur- rently exist throughout the state.' I have done some experimentation using direct methods of measuring Some indicators of excessive water stress are: leaf sun avoidance by folding and tighter angle with the petiole (Left), and shrivel of ripening berries (Right). These conditions are to be vineyard ET and have found that K, avoided. values of our vineyards are roughly 75% of earlier published values. Our we operate in the field. Using hours to Fortunately ET0 is readily available K, estimates are very similar to those track irrigation means that we need to on a daily basis from many sources. In determined by Larry Williams (University translate consumption values from California, the CIMIS (California of California), so I recommend using inches into hours using equation #2. Irrigation Management Information his model for Kr .' System) is available at no cost (aside The discrepancy in crop coefficient Estimating water consumption from tax dollars). Daily values can be values has, in my opinion, generated Tracking applied irrigation is easy, obtained from the CIMIS and the some confusion regarding desirable since we have full control over it. On the UC Davis 1PM websites. Use these deficit irrigation levels for winegrape "debit" side of the ledger, though, is resources to locate the nearest CIMIS sta- vineyards. While published results water consumption. The best way to tion to your vineyard, and then stick stating that deficit irrigation treatments determine water consumption is the with the same site consistently. of 60% of full ET, have proven to pro- "ET" approach ET is a friendly abbrevia- Other sources of ET° include private duce desirable wine quality, we must tion for "evapotranspiration," which is a weather stations (in your vineyard, if be diligent in determining what crop long word that simply means: water that you'd like); weather station networks coefficient model they were using. evaporates either from the soil (evapora- run by consultants; newspapers in some If they were using "traditional" crop tion) or from the plant (transpiration). agricultural communities; and maybe coefficient values, their ET, was likely With drip irrigation, almost all ET comes even the winery that buys your grapes. overestimated. That means that their from the vine (because most of the soil ET, is reported in inches or millimeters, 60% of full ET, could actually translate surface is dry), but we still call it ET. which must be translated into gallons into about 80%, using the new crop ET is highly weather-dependent per acre or equivalent irrigation hours coefficient model. A grower who and is increased by solar energy, dry (equations #1 and #2 above) to match our makes the error of applying 60% of full air, and windy conditions. Solar energy accounting for applied irrigation. ET, using the new crop coefficients heats up the vine's leaves and evapora- But obviously we're not growing might overstress the vineyard. tion of water from leaves serves as a grass. We need to convert ET of the Some growers who have been using cooling mechanism. Wind increases ET grass crop to grapevine ET, referred to the old Kc model do not wish to switch to by stirring up the humid layer of air generically as crop ET, or ETc. To get the new, lower values since that would that surrounds each leaf and mixing it ETc values from ET0 values, we multi- change their management factors. That is into the dry surrounding air. ply ET0 by a "fudge factor" called the fine, as long as they remember they're on Contrary to common belief, cool "crop coefficient," Kc. the old model when contemplating weather does not automatically imply ETc = ETo x Kc (4) ' modification of their irrigation strategy low ET, since it is the capacity of the air As grapevines are planted in rows based on more recently published to absorb additional water that most and are more water-thrifty than research. Again, consistency is more closely affects ET and not the air tem- grasses, the crop coefficient is always important than accuracy, and what has perature itself. However, cool air holds less than 1.0 (some fraction of full ET 0). been working for a grower in the past less water than warm air, so there is Unfortunately, the crop coefficient is should continue to work in the future. generally a reduction of ET during cool not a fixed number, and it is dependent To aid in implementing an irrigation periods, although cool temperatures at mostly on vine size (or leaf area index). strategy, another factor, the manage- low relative humidity will still present Since the leaf area index of a vineyard ment factor (Km), is used in addition to a significant driving force for ET. changes with time of year and trellis Kc. Our ET equation now becomes: ET can be determined by many type, site vigor, row width, ET° x Kc x Km methods, but the most commonly used etc., K, is (5) not a very easy term to pin down. method is called "reference ET" or ET,. The good news is that, after years of la is irrigation to be applied in units Reference ET uses weather-measuring research into obtaining accurate crop of inches (or whatever units ET, is in). equipment to estimate a value of ET for coefficients, I've concluded that consis- The Km value is chosen to reflect the a "reference crop" consisting of well- tency is more important than accuracy percentage of ETc that is to be applied watered, mowed grass. For more infor- when determining Er (80% of ETc equals a Km of 0.8). Km can mation on ET,, consult Reference #4. a. The reason for this is that we can think of ETc as an be changed at veraison for pre- or ost- veraison deficit strategy.

Any errors in ET estimates can be Soil texture plays a large part in soil since water is applied from a point source • absorbed into the Km since it is set water-holding capacity, as does soil and not uniformly across the surface. arbitrarily and experimentally. It is (and rooting) depth. Generally speak- Some irrigation scheduling systems very important that records be kept ing, sandy soils have low water-hold- use a soil-water content approach to from year to year so that the Km ing capacity per foot of depth, while trigger each irrigation event, but with value can generate a consistent ET- clay and loam soils have high water- drip irrigated vineyards at Gallo of based schedule. Sonoma, we have found this approach To make scheduling easier, crop holding capacity. Given any require- to be difficult and unnecessary with coefficient and management coefficient ment for irrigation, soils with low drip-irrigated vineyards. However, the values can be embedded in a spread- water-holding capacity will have to be soil-water content approach more sheet or database irrigation scheduling irrigated with lower volumes more directly addresses the issue of irriga- program. Then, the only inputs needed frequently than soils with high water- tion frequency, as irrigation events are on a daily basis are ET, and hours irri- holding capacity (which can be triggered by soil-moisture content levels. gated. Irrigation requirements are irrigated with greater volumes less A better method is to monitor mid- frequently). day leaf water potential with a pres- determined by subtracting hours irri- Irrigating with a volume beyond the sure chamber daily, following an irri- gated from the hours of ET,. water-holding capacity of a soil will gation event. Examine both weak and One does not need to go back to the waste water through percolation below stronger sections of a vineyard to see if beginning of the irrigation season to the root zone or through run-off. vines are becoming temporarily determine how much to irrigate the next Approximate values of water-holding stressed between irrigation events in day or week. It is sufficient to use capacity can be found in references,' but weaker areas. If so, reduce the time between one and two weeks of irriga- with drip irrigation, it is difficult to deter- between irrigations a day or two while tion and ET, history (using a sum of ET, mine how much soil volume is wetted, cutting back on the volume accord- and a sum of irrigation hours over that ingly same time period). For those who do not wish to create their own computer- 1 '1 based scheduling system, there are sev- eral references for irrigation scheduling software on the CIM1S web site.

. • • C

How often to irrigate he . • c

While the most critical (and difficult) . in . • CT p part of irrigation scheduling is determin- ( a . ing the irrigation quantity required, it is te . R2 = 0.77

Ra

A . also important to know how often irriga- . ion tion should be applied (irrigation fre- t a quency). In other words, if a ET, model 0 . .. . 0 indicates that 18 hours are needed in one long • • E . week, do we apply three six-hour sets, two t : . nine-hour sets, or a single 18-hour set? 0 N hoo . . S

While water use (ET,) is controlled 6 .....• by the vine and weather conditions, —5.0 —6.0 —7.0 —8.0 —9.0 —10.0 —11.0 —12.0 —13.0 irrigation application is limited by soil Midday Leaf Water Potential (bars) properties. Selection of irrigation dura- tion and frequency is highly dependent Figure Shoot tip elongation rate plotted against midday leaf water potential. on soil water-holding capacity. Measurements were taken in 2003 in Sonoma County vineyards for three varieties (Merlot, Cabernet Sauvignon, and Pinot Gris). Regression line indicates a strong relationship between shoot elongation and midday leaf water potential, with elongation ceasing at about -10 to -11 bars.

Figure 111-2

Figure III: Shoot tip ratings of vine water status. Fig. 111-1: Active shoot growth; tendrils reach past growing tip; basal tendrils turgid; Leaf Water Potential (LWP) > -8 bars. Fig. 111-2: Slowing shoot growth; tendrils even with growing tip; basal tendrils turgid; LWP -9 to -11 bars. Fig. III-3: Ceased shoot growth; leaves extend past growing tip; basal tendrils turgid to slightly droopy; LWP -12 to -13 bars. Fig. 111-4: Dead or missin shoot tip; basal tendrils droopy or falling off; leaf-petiole angle becomes smaller; LWP -14 to -15 bars. It becomes less important to monitor Water that percolates below the root It is difficult to state, as a rule of soil-moisture profiles and/or day-to-day zone can move laterally below the thumb, how long is "too long" between vine water status once a good feeling for ground (especially on hillsides), result- irrigation events, as it is highly depen- the irrigation constraints is obtained. ing in areas deficient in water and dent on soil characteristics. "Too long" areas with surplus water. This wastes could range from a couple of days to a Irrigation efficiency and uniformity water and can result in groundwater couple of weeks. Use soil moisture Irrigation duration and frequency contamination, especially with regard probes or, as discussed earlier, pressure directly influence application effi- to nitrates that move readily down the chamber measurements to evaluate the ciency and, in the case of hillside vine- soil profile. Furthermore, the differen- drying cycle between irrigation events yards, application uniformity. There is tial quantities of water at the top ver- and learn about your vineyard. frequently confusion over the two sus the bottom of the hills will increase Changing weather patterns are terms: uniformity and efficiency. They nonuniformity of vine growth. common in coastal grapegrowing are not synonymous. As for irrigation efficiency, vineyard regions, and cool weather should not Uniformity refers to the equal distribu- and soil spatial variability must be con- be seen as an excuse to cut back on tion of irrigation volume throughout a sidered. Weak areas in vineyards are water. Remember that water consump- vineyard beingyrigated. In other words, if often caused by gravel or sand streaks, tion is determined less by temperature application uniformity is perfect, all vines or by shallow soils on hilltops, or other than by humidity, sunlight, and wind. would receive the same volume of water. changes in soil texture or depth such as Keep to your ETc model even during On the other hand, efficiency refers to those that occur during land develop- cool weather or you will be caught the amount of applied water that is avail- ment. The weakest or shallowest soils short during the heat wave that follows! able for uptake by vines. If efficiency is need to be focused on when determin- perfect, all water applied during each irri- ing the maximum irrigation duration, B. MONITORNG VINEYARD WATER STATUS gation event will be available for uptake. since any irrigation beyond what can Irrigating without monitoring vine- In reality, it is not possible to achieve be held in the weak zone may result in yard water status is like driving a car perfect uniformity or perfect efficiency. vineyard nonuniformity. blindfolded. That analogy may be But we need to be aware of these factors A common mistake is to apply more tired, but it's very fitting. In irrigation so that we can maximize them. water to weak areas by adding extra scheduling, our best efforts at deter- Application nonuniformity is com- emitters. However, weaker areas of a mining water consumption through mon in hillside vineyards due to vineyard actually consume less water ETc are still an approximation. We delays in system filling at startup and than stronger areas due to less foliage need to watch the vineyard to deter- system drainage at shutdown. It can being present, so extra watering does not mine its response so we can make cor- also arise from variation in emitter dis- make sense. rections, if necessary, during the season charge rates due to pressure differ- Our goal is to produce and maintain and in seasons to follow. ences and/or clogging, although good vineyards of uniform vine size, so we While many years of experience will system design and maintenance need to apply the same amount of allow a vineyard manager to expend should minimize that problem. (Refer water throughout the vineyard, regard- less effort on vineyard water status to Reference #1 and #3 for more infor- less of soil water-holding capacity. monitoring, some monitoring will mation on system design influence on The the best way to manage around always benefit vineyard health and sup- irrigation uniformity). variability is to irrigate so that the port an irrigation strategy (see Section C, In order to maximize uniformity, irri- regions of low water-holding capacity May/June 2005 PWV). are not irrigated beyond what they can gation should be held off until the Soil moisture monitoring is a tradi- hold. This can be accomplished by irri- required application is of sufficient dura- tional way to measure water status of gating with shorter, more frequent irri- tion (six to eight hours), that the fill and agricultural systems. But in most agri- gation events that maintain more con- drain times of the system are only a small cultural applications, the soil moisture sistent moisture availability in the percentage of the total irrigation duration is maintained close to field capacity. By weak soil areas while providing the Application efficiency is defined as the contrast, in winegrape growing we do same quantity of irrigation to the entire percentage of applied water that is avail- not always want to maintain a high field. able for vine uptake. While efficiency is water status of vines (see Section C). reduced by evaporation from the soil sur- In general, longer, less frequent irri- Furthermore, in drip-irrigated vine- face, this loss is minor with drip irriga- gation events will reduce irrigation efficiency, while increasing application yards, the wetted soil volume is usu- tion. The primary cause for reduced effi- ally discontinuous and, as a result, ciency is loss due to runoff and/or deep uniformity. This contrasts with shorter, there is great potential for measure- percolation below the root zone. more frequent irrigation events that increase irrigation efficiency while ment uncertainty, depending on loca- decreasing application uniformity. tion of the sensor with respect to emit- Soil can be thought of as a sponge ter position, not to mention the Applying water faster than it can be When using drip irrigation, it is variability in soil properties through- absorbed results in surface runoff. As N, important not to extend the duration out any vineyard block. Consequently, the soil becomes saturated at deeper between irrigation events too long, no it is generally advantageous to monitor and deeper levels during an irrigation matter what the goals are for deficit irri- the vines rather than the soil. application, its infiltration rate gation (see Section C). After winter rain- Hence, this discussion will focus decreases, potentially resulting in fall is depleted and the remaining soil primarily on vine monitoring using water runoff from the target location. water comes from irrigation, there is only instruments and visual assessments. Additionally, applying more water a small water reservoir available to each But first, a few points about soil mois- than the soil column can hold in its vine, and ready water-availability during ture methodology. pores results in deep percolation like periods of hot weather is crucial to pro- seepage out of the bottom of a satu- tect vines against heat damage. rated sponge. Soil moisture measurement does Soil holds onto water like a sponge Remember that since these are neg- have its place in drip irrigation sys- and, as happens with a sponge, it is more ative numbers, "greater than" means tems. It can be used early in the season difficult to extract water as the soil "less negative than" and "less than" after winter rainfall has uniformly wet- becomes dryer. Hence, there is a tug-of- means "more negative than." ted the soil profile. That is probably the war between the soil and the atmosphere, While the pressure chamber is an single most useful time of the season with the vine stuck in between like the easy-to-use instrument, there are a few for soil moisture monitoring. Irrigation rope. So, the dryer the soil becomes caveats required for accurate measure- initiation decisions can be based on and/or greater the "evaporative ment, not the least of which is making waiting for soil moisture levels (either demand" of the air becomes, the stronger sure to bag the leaf on the vine before water content or water potential) to the suction on the water column will be. removal. Vine water status is likely to reach a specified threshold after being ruction can be expressed in units of vary considerably throughout a vineyard depleted from winter rainfall storage. pregiture. Actually, negative values are used block. Be sure to sample numerous loca- In regions where the soil profile is not becauSe suction is synonymous with nega- tions within a vineyard to get either a completely filled by winter rainfall, as on tive pressure. Commonly, water potential is composite value for the block or to map the north coast of California, soil mois- expressed in units of bars (1 bar is approxi- out zones of similar water status. ture monitoring is useful in gauging mately equal to one atmosphere). As a rule of thumb, sample at least one when to commence irrigation or how In scientific journals, Megapascals location per acre for very small blocks (less much irrigation is needed to refill the soil (MPa) are most commonly used. Don't than five acres) down to one location per profile by budbreak But remember that let that throw you off; to get bars from five acres for larger blocks (about 100 once drip irrigation has begun, the read- Megapascals, just multiply by 10. It is acres). At each location, take measure- out of the instrument no longer repre- even more common for people to leave ments on two leaves. If they are within 1 sents the entire horizontal extent of the off the negative sign from the bars in bar of each other, log the average and root zone of the vineyard. casual conversation. That is technically move on to the next site. If not, take a third Instruments that measure soil water incorrect but since everyone does it, it measurement. If there seems to be an out- content include the Neutron Probe, is acceptable. Larry Williams provided lier that differs more than 2 bars from the Time-Domain Reflectometry (TDR), and a good overview of the pressure cham- other two, discard that measurement. Capacitance (dielectric) Probes. For mea- ber in a previous PWV text.6 Refrain from making measurements suring soil water potential (suction pres- The beauty of the pressure chamber is on abnormally hot and dry (or windy) sure), soil-moisture blocks and tensiome- that it is easy to learn, requires no power days, when even well-irrigated vines ters are available. All of these source, and is portable. Just mount it to will produce measurements that sug- instruments have some associated error. an ATV and take it where you want to go. gest they are stressed. Conversely, It is best to consider these measurements Measurement is made by sampling — measurements taken on cloudy or foggy as site-specific — each site should be cutting off — an exposed, fully expanded days will give meaningless values. "calibrated" independently. This is yet leaf. Before sampling, though, it is impor- At Gallo of Sonoma, we generally another strike against soil-moisture mea- tant to endose the leaf blade in a plastic wait at least one hour after the fog lifts surement. For more discussion about sandwich bag immediately before it is to begin pressure chamber measure- soil-moisture monitoring methods, con- removed. This crucial step is often disre- ments and do not take readings when sult references #2 and #4. garded, and can create substantial mea- it is even partly cloudy. surement error if not done. Finally, realize that water potential Vine water status monitoring A leaf is cut off with a razor blade is a measurement of the suction force There is no better indicator of how and placed in the chamber, bag and all, in the vine. Vines have built-in drought your vineyard is doing than the vines with the cut end exposed. The chamber resistance whereby they close their themselves. I've found that the pres- is slowly pressurized until the petiole stomatal pores in the leaves when sure chamber is, by far, the preferable sap just reaches the cut surface. If done water stress is imminent. Water flow method for monitoring vine water status. correctly, the pressure in the chamber decreases when stomatal closure A pressure chamber (also called "pres- that is read off the gauge is equal to the occurs and that tends to decrease the sure bomb") should be available to most suction that was in the xylem vessels suction force. This situation could be winegrape growers, either owned or before the leaf was removed. It takes misread as a non-stressed condition. through a service. The pressure chamber some practice, but it is a skill that can be Measuring stomatal conductance is a portable, relatively low-tech and low- learned by almost anyone. requires the use of an instrument called cost instrument that measures water Measurements should ideally be a porometer, which is a fantastic tool potential of the vine at the location it is taken about mid-day. I have found, how- but hardly practical for a grower. I sug- sampled (usually the mid-shoot leaves). ever, that the hours of noon to 3:00 work gest, to avoid misreading a highly What is water potential? To under- well for reliable readings. The main thing stressed condition, that frequent (at stand it, you must first understand that is to do it — and do it regularly. least weekly) pressure chamber mea- water is not pushed through the vine, It is difficult to make general specifica- surements be made in addition to care- but is sucked through the vine. Suction tions about interpretation of water poten- ful attention to visual symptoms. arises in the leaves, where liquid phase tial measurements, although strategies water evaporates. Recalling the discus- will be discussed in Section C. As a general Visual water status assessment sion about ET, the dryer the air sur- guideline, the following may be used: The second vine-monitoring instru- rounding the leaves, the greater the ment is located between and in front of evaporation rate is. The water suction Greater than —10 Bars No stress your ears. Visual symptoms of water force is transferred throughout the vine —10 to —12 Bars Mild stress status are reliable and cost nothing that, in effect, has a continuous column —12 to —14 Bars Moderate stress of water from roots to the leaves —14 to —16 Bars High stress through the xylem, or water-conduct- Less than —16 Bars Severe stress ing vessels.

79 MARCH/APRIL 2005 GR APEGR OWING

Integrated irrigation is programmed to avoid sun exposure Section C — Irrigation Strategy will at such times. This mechanism helps appear in May/June 2005 PWV. Continued from page 34 prevent overheating of the leaves. beyond your time. It is time well spent Under high water status (not stressed), The author wishes to thank the Gallo to look for signs of both excess water the petiole makes a 90° angle with the family for their tremendous support and stress and, on the opposite extreme, leaf blade. The angle becomes smaller the staff of Gallo of Sonoma Winery & signs of excess vigor brought on by too and the leaf folds slightly under high Vineyards for their substantial contribu- much easily extractable water. levels of water status. This is another tions. Special thanks to Jim O'Donnell for By far, shoot tips are the best indica- indicator of an over-stressed condition his invaluable efforts on the research pro- tors of water status, especially (and pri- — vines in this state are not very pro- jects. Additionally, the content reviews marily) between bloom and veraison ductive. from Stan Grant, Jeff Lyon, Steve Matthi- (when we are trying to restrict shoot However, some varieties, such as asson, and Kirk Grace are sincerely appre- growth). Shoot tips are easy to observe Cabernet Sauvignon, do not express ciated. just by driving past, although more this symptom readily. Thus, it is not a References thorough examinations are best. very reliable indicator of water status. 1. C. M. Burt and S. W. Styles. 1999. Drip Shoot growth ceases at about -11 Actually, all of the visual symptoms of and Micro Irrigation for Trees, Vines, and Row bars of water potential, but will show water stress are "lagging indicators" in Crops. ITRC, Cal Poly, San Luis Obispo, CA. signs of sloWing at -9 or -10 bars that they express themselves after the 2. Irrigation Scheduling: A guide for vine has experienced some stress. (Figure II). Beyond about -14 bars, Efficient On-Farm Water Management. D. A. The fruit can be used as an indicator shoot tips will dry up. This is not a bad Goldhamer and R. L. Snyder, Eds. 1989. of water status although, again, fruit- thing if the shoots are long enough and University of California publication 21454. stress symptoms are often an indica- have enough leaves to ripen the crop. 3. Micro-irrigation of Trees and Vines. L. Like the pressure chamber, shoot tips tion of an over-stressed condition. Schwankl, B. Hanson and T. Prichard, Eds. may be used as a "speedometer" for Before veraison, fruit water-stress 1996. University of California publication irrigation management, although they symptoms indude flaccid or shriveled 93-03. are not useful after growth ceases. berries in the afternoon. This is not nec- 4. Scheduling Irrigations: When and How At Gallo of Sonoma, a rating system essarily an over-stressed symptom, Much Water to Apply. B. Hanson, L. is used to describe and log shoot tip though, if the berries regain turgidity Schwankl and A. Fulton, Eds. 1999. Uni- condition (Figure III). There are other in the evening. In fact, this condition versity of California ANR publication 3396. systems in use, but they are all very can lead to small berries that will make 5. Snyder, R. L., B. J. Lanini, D. A. Shaw, similar in concept. a more highly structured red wine, if and W. 0. Pruitt. 1989. Using reference evapo- As discussed in Section A, a very desired. transpiration (ETo) and crop coefficients to esti- good method for assessing vine water After veraison, puckering or shriv- mate crop evapotranspiration (ETc)for trees and stress early in the season is to monitor eling berries are usually an over- vines. Cooperative Extension, Univ. shoot elongation rates using numerous stressed condition. During ripening, California, Berkeley, CA, Leaflet No. 21428. marker shoots within a vineyard block. flaccid or shriveling berries will never 6. Williams, L. E. 2001. "Irrigation of Shoot growth will slow down and then recover their turgidity and can result in Winegrapes in California." Practical Winery stop — usually before the shoot tip severe loss of both yield and wine & Vineyard. Pp.42-55. symptoms appear. quality. 7. Monthly Station Normals of Tem- Other visual indicators include ten- However, it is important not to con- perature, Precipitation, and Heating and drils, which droop when the vine is fuse shrivel due to water stress with Cooling Degree Days 1971-2000. 04 Cali- water-stressed. Tendrils are useful only shrivel due to other conditions. Shrivel fornia. National Oceanic and Atmospheric before veraison, however, as they due to water stress will be seen on fruit Administration. National Environmental become tough and woody afterwards. all over the vine, while fruit shrivel Satellite Data and Information Service. Basal leaves (leaves dosest to the base of due to overexposure to sunlight (heat National Climatic Data Center. Asheville, NC the shoots) will abscise (turn yellow, dry stress) will be most prevalent on the 8. Historical Climatology Series 6-4. up, and fall off) when a vine is under afternoon-sun side of the canopy. Climates of the World. 1991. National water stress. This is undesirable, as Fruit shrivel due to bunch-stem Oceanic and Atmospheric Administration. leaves are needed to protect the fruit necrosis will be accompanied by a National Environmental Satellite Data and from the sun and for production of sug- dried out rachis, while water-stress Information Service. National Climatic ars for ripening. Hence, yellowing leaves shrivel will retain a green rachis. Since Data Center. Asheville, NC. are usually a sign of over-stressed vines, fruit shrivel during ripening is poten- Web Sites although a small amount of leaf abscis- tially catastrophic, it should be moni- California Irrigation Management Infor- sion — no more than one to two leaves tored but not used routinely as an irri- mation System (CIMIS): www.cimis.water. per shoot — may be allowable if it occurs gation guidance tool. Late in the ca.gov/ late in the season. season, the pressure chamber is really UC Davis IPM — California Weather Leaf blade-petiole angles will the only reliable tool for vine water sta- Databases: www.ipm.ucdavis.edu/WEA ■ change under water stress, as the vine tus feedback. THER/weatherl.html ZOI 6 JULY/AUGUST 1995 PWV ININEGROWING by Michael Porter priate action. This means confirming one (or more) basic cause(s) and ruling out others. Diagnosis should be based ine stress problems encountered Dealing with on observation and/or analysis (as op- in North Coast, California vine- posed to speculation). Untangling a yards late in the season are knotty problem can be difficult. frequently misdiagnosed. A mis- Beware of the quick fix. Unfortu- diagnosed problem cannot be nately, all too often, someone unfamiliar effectivelyV treated. with a vineyard arrives on the scene and late-season reaches a quick diagnosis based on su- For example, you've made it through budbreak, frost, bloom, and veraison. perficial evidence. It is difficult to diag- The crop looks good as you tour the nose stress symptoms based on one vineyard a couple of weeks before har- visit. How the stress pattern develops vest, but then you notice some leaves can be diagnostic of the cause. While vi- turning yellow. Or maybe you have a vine stress sual symptoms sometimes point to an problem with slow ripening or high pH obvious cause, just as often they are am- fruit. Maybe the vines are suffering from biguous, pointing to several possibili- "stress." But what's the real problem? ties. When in doubt, use analysis and What's causing the stress? What should observation. you do? Too often people assume the above Appropriate diagnoses symptoms (or others) of vine stress re- To diagnose the cause of nutrient sult from water deficit and irrigate, but problems, soil and tissue analysis are ex- lack of water may not be the problem at The fact that many people assume cellent tools when combined with ob- all. With grapevines, as always in biol- that vine stress is synonymous with a serving foliar symptoms. However, ogy, it is useful to take in the big picture soil moisture deficit may be due to the neither lab results nor visual observa- — to step back and recognize that any history of viticulture research and train- tions are sufficiently reliable to be used problems are part of a complex web of ing in California. In the San Joaquin and alone. Labs can make mistakes, and interaction of many diverse factors. The southern desert valleys, where most viti- their interpretive standards are typically real cause of the symptoms may not be culture research has been done, the most based on Thompson seedless — which simple to find, and the solution might common kind of stress may well be is particularly inappropriate with regard not be obvious, but once you've figured moisture deficit. But in the North Coast, to potassium and magnesium for fine out the cause, the solution you apply is it is just one of many kinds of stress, and wine grapes in the North Coast. much less likely to compound your dif- it's not the most common. Too little or too much soil moisture ficulties! Therefore, irrigating in response to can be a problem, but looking at the soil Late season symptoms in North Coast stress symptoms is appropriate to com- surface provides minimal information. vineyards often fall into three general modity viticulture in the San Joaquin You must actually check soil moisture in groups: visual foliar "stress," slow rip- and southern desert valleys, but it the root zone when problems arise ening/delayed harvest, and high pH should be considered carefully before (if not sooner!). Monitoring moisture at fruit/wine. These symptoms have sev- being applied in cooler and higher-rain- different depths over time, a neutron eral possible causes, but in each case, we fall regions, particularly when the goal probe provides excellent information. have a tendency to blame one cause and is producing fine wine. For spot checking, the minimal test re- treat for it. As a result, the true problem Misdiagnosis of the source of foliar- quires a shovel, a backhoe or auger goes uncorrected, and the vines suffer stress symptoms often leads to inappro- would be better (to determine the loca- the consequences of unnecessary — priate action. At best, the nostrum may tion of the root zone). sometimes harmful — treatment. be of psychological benefit to the Diagnosing root pests and pathogens grower, but only a bandaid for the normally requires sampling roots on Foliar stress symptoms vines. At worst, one can do significant problem vines (with the possible excep- Few commonly used terms in viticul- harm. (Irrigating stress symptoms tion of young vines damaged by go- ture are in greater need of clarification caused by root pathogens, such as phy- phers). In the North Coast, phylloxera is than "stress."' The word is most often topthora, pythium, or verticillium, is a common root pest that can often be di- used when some leaves turn prematurely like putting out a fire with gasoline!) agnosed this way. yellow, usually after veraison (but some- The cause of stress symptoms must be Of the root pathogens, oak-root fun- times before). The possible causes of the discovered in order to determine appro- gus can sometimes be diagnosed in the symptom are many: insufficient soil field. It produces a white fuzzy coating moisture, excessive soil moisture promot- 'For background and some detail on these issues, easily visible on the roots and a charac- ing root pathogens, potassium deficiency, read the first three articles in this series in PWV: "Soil Origin" in March/April '94, "Soil Fertility teristic fresh mushroom odor. Where salt or boron toxicity, or phylloxera, to and Vine Nutrition" in May/June '94, and "Soil vine symptoms suggest possible infec- name a few. Too often they get lumped Moisture and Water Management" in March/April tion with phytopthora, pythium, or ver- together as having one likely cause — soil '95. Lucie Morton and Richard Smart are also rec- ticillium, fresh samples are best moisture deficit stress.' ommended reading. delivered to aathologq lab for culture 8 JULY / AUGUST '995 PWV WINEGROWING

and identification. Among above- ground pathogens, eutypa and Pierce's disease are often recognizable on-site. On the other hand, you will likely need DISTURBING SYMPTOMS IN YOUNG VINES help from the pathology lab to confirm botryodiplodia, and possibly for pho- A t this time, some young vine presence of dark spots in the xylem of mopsis on shoots and petioles. A yards in the North Coast are ex- the rootstock, which appear black vi- periencing severe decline and vine sually, but are orange or golden in Slow ripening/delayed harvest loss due to one or more unconfirmed thin section when back-lighted. Many Factors affecting the rate of ripening causes. Foliar symptoms on these of these vines show little or no callus- include crop and canopy management, vines often resemble leaf-roll virus ing at one or more disbudded nodes LRV, weather, soil moisture, and mineral (LRV), except that shoot-stunting and apparent "heart-rot" of the pith is nutrition. Thinning the crop at veraison and vine death far exceed the patho- present. These vines test positive for or later can help compensate for the prob- logical consequences normally asso- saprophytes (decomposers). lem, but throwing away fruit has an eco- ciated with LRV. In addition, many Don't simply assume that if your nomic down-side that is difficult to dying vines test negative for LRV, young vines are dying, this "new ignore. Diagnosing and correcting the and some are certified clean stock disease" is the culprit, however. source of the problem is generally prefer- The vineyard rumor mill is cur Many young rootstocks fail the cri- able to dropping grapes on the ground. rently chugging along at full steam, teria for selecting wood for root- Problems arising from poor canopy claiming the new disease is a virus, stock cuttings in A.J. Winkler's Gen- microclimate have been thoroughly dis- fueled by arguments such as "It eral Viticulture (p. 199 [2nd edition]). cussed by Richard Smart and need not looks like virus, and we don't even Winkler warns against "very long be repeated here. The desert shade trel- know how many viruses there are internodes indicate very rapid lis (the three-wire T trellis designed to beyond those few that we know how growth; such canes are usually soft shade fruit from the burning desert sun, to test for." This debate will only be and poorly nourished, hence low in which fosters mildew and botrytis in the resolved through research (with in- stored reserves (starches and sug- North Coast region) should not have ternational collaboration, I hope) to ars)," and says, "When the cane is been adopted as the "standard" in the discover the real cause of this dis- cut, the inner bark should appear North Coast. Its problems are exacer- ease, not through speculation. green and full of sap; the wood firm, bated by over-stimulation with irriga- Other possible infective agents well-stored with reserves, and free tion and application of nitrogen, as well and modes (see below) are being from dark specks. ... Canes that are as the use of 'kicker' canes above the vigorously scrutinized, but none as unusually flat or angular in cross main fruit zone. Severe hedging and leaf yet, including the "latent virus" con- section should be avoided." The io- pulling, however, can also inhibit ripen- jecture, have satisfied the require- dine test for starch described in the ing by leaving too little leaf surface area ments of Koch's postulates for con- footnote on the same page is highly in proportion to crop load. firming what disease is affecting recommended. Leaf-roll virus has long been known these vines: 1) isolation of pathogen It is unclear, at this time, why to inhibit normal ripening, and more re- from`rom diseased tissue, 2) character- these failing vines show poor callus- cently mealy bugs have been identified ized in pure form, 3) introduced into ing and/or xylem blockage. It may as a vector. Fortunately one can test for a healthy individual, 4) that indi- be that immature, poorly nourished LRV, and when it's confirmed, can re- vidual develops the disease, 5) the cuttings are slow to callus and easily move diseased vines. pathogen is recovered from the now- infected by saprophytes in moist soil Unfortunately, many people choose to diseased, formerly-healthy indi- in the North Coast. It may be that assume LRV is present because of foliar vidual. Until these criteria are met, callus formation is being inhibited symptoms, which can be misleading no theory can be considered defini- in some vines due to improper con- (see sidebar on young vines). tive. "Virus-like symptoms" and ditions at the nursery, or by infec- Other problems do look like LRV and even the presence of the virus itself tion by virus, fungi, or bacteria. can be tested for. (Testability is basic to do not prove that it is causing the It may be that we have wide- scientific methods; untestability is more vine decline. spread, but as yet unrecognized, in the realm of religion. Those having Other possible causes include se- diseases such as new and more viru- faith in unconfirmable conjectures vere potassium deficiency (on Clear lent forms of eutypa, esca, myco- should recognize the thin ice on which Lake clay, for example), which can plasmas, botryosphaeria, dema- they skate.) cause stunting and curled leaves. tophora, flavescence doree, botryo- Also blockage of xylem, can lead to diplodia, or others. The jury is still Potassium deficiency severe foliar potassium/leaf-roll out, but until an infective agent is The most common North Coast prob- symptoms, even where soil potas- confirmed as the cause, I favor the lem visually mistaken for LRV is potas- sium is quite adequate. simpler theory that thin, flat, imma- sium deficiency, with phosphorous One common symptom associated ture plant material is the principle deficiency a distant second. The prob- with decline of young vines is the culprit. lem is often primary, resulting from low soil K and/or very high magnesium. We 220 10 JULY /AUGUST 1995 PWV WINEGROWING

have been successful in rescuing some season (or not to) should be made on a every year, however, we typically find vineyards from the bulldozer by correct- site-specific basis, based on analysis of one or more other problems: high water ing the nutrient problem and watching available soil moisture, crop load, peti- table, poor canopy, over-irrigation, LRV, the "virus" symptoms disappear. ole K/Mg, the weather, wine style/mar- and so on. Where these other potential K deficiency is also often secondary; ket niche, and so on, and may change problems have been addressed, one can that is, it is frequently caused by root from year to year. In any case, curing expect to be caught by the changing sea- damage (e.g., very wet soil, phylloxera, your vines' K deficiency, if they are de- sons less often and for the effects to be phytopthora) or xylem blockage (see ficient will go a long way toward reduc- less severe. sidebar on young vines). As before, fix- ing the "need" for late-season irrigation. ing the problem requires that the cause High pH be correctly diagnosed. There are no Weather Much has been said and written about "standard" actions, no panaceas. Excessive soil moisture available to the problems associated with high pH Potassium deficiency is often misdiag- vines late in the season also delays rip- fruit and wine, somewhat less about nosed as soil moisture deficit. This often ening. Inappropriate irrigation may be how they come about and how to avoid occurs where K deficiency has been the problem yet again, but natural the problem. wrongly ruled out — typically by a lab causes could be the problem, too. In Unusually slow ripening (discussed or advisor relying on criteria established some years, a sudden and dramatic above) can lead to high pH, as the nor- for Thompson Seedless — or where no cooling of the weather (often accompa- mal rise in pH and associated decline in analysis has been done at all! nied by cloud cover and some rain) titratable acidity (TA) are not balanced Those relying on desert commodity leaves many North Coast grapes hang- by a commensurate increase in sugars. nutrient criteria routinely rely on desert ing on the vine, gaining sugar at a Conversely, a too-rapid rise in pH, due commodity irrigation criteria, too, snail's pace. This typically happens to excessive accumulation of K ions in which can be summarized by "when in some time in October and is a particular the fruit, can outpace the gain in sugars. doubt, drown 'em out." (In fact, it nuisance when it is early in the month (We should note that both can occur si- would be just as inadvisable to adopt a (1994) or when most vineyards are late multaneously.) The latter subject de- prohibition on late irrigation.) due to a cool, wet spring (1991). serves closer examination and, perhaps, The decision to apply water late in the In vineyards where this occurs nearly more research. Many people are familiar with Roger Boulton's work on the subject, especially regarding the movement of K ions into the fruit and substitution for H ions, re- sulting in a drop in TA and rise in pH. he horse is here to stay, Far fewer have heard that the study vines were subjected to severe moisture deficit — to the point of defoliation. As the vines underwent premature se- but the automobile is only nescence (leaves turned yellow and fell off), K was moving out of the leaves at an abnormal pre-harvest rate, with a novelty -a fad. some of it ending up in the fruit. Many people have come to view K as the Or•sid•nt of Michigan source of the problem, but I am con- Savings Bank advising vinced that K movement into the fruit is Henry Ford's lawyer not secondary to the premature senescence.

to inv•st In th• Ford Had the leaves stayed green and re-

Motor Company. mained on the vines, far less K would have ended up in the grapes! Consider for a moment Richard Smart's work with dense, shaded cano- pies. He observed that interior leaves re- ceiving too little light turned yellow and fell off — and in the process moved K back into the vine, some of which ended up in the fruit, resulting in undesirable [ 451, SUPREMECORQ high pH. It would be incorrect to blame the problem on K, as it is merely a link in the shade/senescence/K mobilization/ The new tradition high pH process, but it is not the origin of the problem. High fruit K and pH are For information about the benefits of SupremeCorq, call 800 794 - 4160. effects — leaf senescence due to shading PWV JULY/AUGUST 1995 11

Michael Porter has worked as a winemak or water stress is the cause! • • What the two above problems have in ing assistant, and as a research assistant at • • common is premature senescence of Crocker Nuclear Lab, UC Davis while study- • MOVING ??? • leaves, leading to increased mobilization ing Physics at Cal State University-Chico, • Tell us...Write us: • • • of K out of the leaves and into the fruit followed by a masters degree in Earth Sciences • Pracfical Winery & Vineyard • and, ultimately, to high pH fruit and from Chico. He has taught geology, meteorol- • 15 Grande Paseo • wine. I propose that the problem is pre- ogy, oceanography, physics, and astronomy in • San Rafael, CA 94903-1534 • mature leaf senescence and that K is junior colleges. Since 1984, he has worked • Let us know so that you will • with Bob Uttermohlen to provide soil fertility, • • guilty only by association! High wine K • continue to receive your • vine nutrition, and water management con- subscription at your new address. • and pH are symptoms of a more com- sulting services. • plex process; K is not the culprit but rather one link in a web of interactions. I have analyzed bloom and veraison petioles and observed foliar appearance, BOTTLING then compared them with fruit/must FILTRATION & pH in many North Coast vineyards for a number of years. The results are quite PROCESSING intriguing. EQUIPMENT Contrary to the simple model that high vine K causes high wine pH, we have ob- served little direct correlation between those two variables. In fact, the most problematic, high pH vineyards com- monly have moderate to low petiole K. More significantly, these high pH vines usually have very low K/Mg ra- tios and show post-veraison K defi- ciency symptoms — including KHS FILLERS premature senescence! Though it KHS ORION FILTER sounds counter-intuitive, low vine K (relative to Mg) can result in high fruit K, hence high wine pH. In such a case, improving vine K/Mg status can help avoid premature leaf senescence, result- ing in a lower wine pH. (For more on K/Mg ratios, see PWV, May/June 1994.) The eminent biologist Garrett Hardin long ago noted that, "Counter-intuitive solutions are common when we are dealing with biological problems." Of course, the best place to do field trials is in your own vineyard. ARMBRUSTER

A word of caution If your vines show pre-harvest yellow- • KHS/H&K - Bottling & Packaging Equipment ing due to moisture deficit (a la Roger • PRIORITY ONE - Palletizers/Conveyors/& Labellers Boulton) or dense shade (a la Richard • KHS - Filtration Equipment Smart), increasing the vine K content could easily result in more K being • OMESS - Pressure Leaf D.E. Filters moved into the fruit and higher wine pH. • ARMBRUSTER - Stemmer/Crushers & Mash Pumps If your vines experience premature senes- • BEER - Capsule Dispensers & Heat Tunnels cence for any reason other than low K/ Mg status, adding K could backfire. rty-u-- If your vineyard has a low K/Mg status and high vigor on a San Joaquin KHS MACHINES, INC. "shade trellis," you should fix the de- 1350 INDUSTRIAL AVE., SUITE G, PETALUMA, CA 94952 ficiency and the canopy! Adding K TELEPHONE: 707/763-4844 TELEFAX: 707/763-6997 and keeping the shade could make things worse — and serve to propa- SUBSIDARY OF KHS AG • BAD KREUZNACH, GERMANY • East Coast Representative: gate the mistaken notion that "K is JUERGEN LOENHOLDT - R.D.1, ROUTE 14, Himrod, NY 14842 (607) 243-7568 bad for wine pH." ■ 121 located at the Prosser research center, to measure moisture use, establish water requirements of wine grapes at varying crop levels, and determine their effect on vine growth, yield, wine quality, and winter hardiness. Wample had taken the study to the next level of refinement. With the help of Stimson Lane Vineyards and Estates and winemaker Doug WASH IN GTON STATE'S RONALD IRVINE Gore of Columbia Crest Winery, together they used a circular 64-acre WINEMAKING WITH WALTER J. CLORE Sauvignon Blanc vineyard near the Columbia Crest Winery overlook- - - - - H 'STORY ing the Columbia River on the lower Horse Heaven Hills slope. They divided the vineyard into quadrants. Within each quadrant, vineyard rows were treated with four varying levels of irrigation. Under this system, four different water treatments were replicated in four different THE IRRIGATION EXPERIMENT locations. Wines wee then made from each of these different treat- ments, beginning in 1992. Gore made sixteen different wines in PROOF IS IN THE WINEGLASS batches of 3,000 gallons each. The water treatments were Low Low (LL), Low High (LH), High -11■ClIt44, APRIL 1994— Low (HL), and High High (HH). LL referred to a low water treat- Four glasses of Sauvignon Blanc sat in front of me waiting to be tasted. ment applied throughout the growing season. LH was low irrigation Their strawlike yellow color twinkled under the glare of the over- head lights. early in the growing season, followed by increased irrigation from the point where control of canopy growth had been achieved through har- I was attending a two-day seminar entitled "Winemaldng in the vest. HL was high irrigation during the early season, followed by Vineyard," put on by the Central Washington Wine Technical Group low irrigation from the point where the low irrigation treatments with support from Washington State University. Toward the middle of showed control of canopy development through harvest. This treat- the remaining day, we were tasting wines presented to us by Dr. Bob ment was similar to standard irrigation practices. And finally, the Wample. The four wines had been made at Columbia Crest Winery by HH treatment referred to high irrigation maintained throughout the winemaker Doug Gore. growing season. Wample jumped up on the stage with the enthusiasm of a thirty- High and low levels of irrigation were defined as 2.2 and 1.2 inches year-old, although he was likely closing in on fifty. He was fit and of water per foot of soil, respectively, in the top three feet of the soil tanned and slightly balding with brown hair brushed to the side. He profile. Even at the high levels, not a lot of water was being added to wore stylish clothes with reading glasses hanging on his chest by a the naturally occurring 7 to 8 inches of annual rainfall. Thus, in the strap. His demeanor was more coach than scholar. Wample was about to accomplish an amazing feat. He was going high-level treatment, the soil received an additional 6.6 inches of water, or a total of less than 15 inches of water, including nature's addition. At to distill all of the detailed information that had been laboriously pre- low levels the total water, including treatment and rainfall, was less than sented to us over the last day and a half into four glasses of wine. In 12 inches. taste, smell, and appearance, tile four glasses of wine would be a pow- Wample provided an aerial photo of the vineyard on the overhead erful metaphor for his ongoing study about the effects of irrigation on projector. It looked like a giant dartboard with concentric circles and grape and wine production. It is a classic (and forceful) teaching tool. lines. Originally named Circle 100, in 1993 the vineyard was renamed Long after the seminar was over we would all remember tasting the the Clore Vineyard; in honor of Dr. Clore. What a fitting tribute! The four wines. They spoke volumes. They were the end result of a study vineyard encapsulates all that Dr. Clore set out to accomplish so many begun in 1982 when Wample joined with Dr. Sara Spayd and Dr. Bob Evans to establish a complicated monitoring system, in a vineyard years ago. Wample also showed a number of graphs to highlight photosyn- thesis of the vi ne during different times of the growing season. He told As water becomes limited, only those crops that use less water and how different water-level treatments affected the vine growth. are of higher value will be allowed to use the available water supply. His talk had three elements of immediate importance to Clearly, we were tasting the future of wine grapes: it was bright and fresh. Washington growers and winemakers. First, by regulating a low irriga- The results of this promising study showed that the Columbia tion treatment early in the season, the grower can better manage vine- yard canopy, which reduces physical management strategies, decreases Valley is one area in the world where growth, production, and quality vineyard diseases and pests, and sets the vineyard up for better hardi- can be manipulated by the grower to produce distinctive, quality wines. ness by limiting the growth of the wood on the vine. Second, the vine- yard uses much less water than the standard irrigation practice has suggested. And third, the results of the various treatments could be easily tasted by growers and winemakers. We tasted the four Sauvignon Blancs from the 1993 harvest. The four wines were from only one vineyard quadrant. Wample asked par- ticipants to indicate which wines they liked best. A clear preference was shown for the wines using the LL and LH. water treatments, with roughly an equal split in votes. Wample smiled broadly; these were the same results he gets whenever he has people taste these wines. I voted for the LH wine. It was fruitier in the aroma, highlighting melonlike fruit aromas with just a bit of the grassy character of this grape. On the palate the wine was rounder and fruitier, with a mouth- filling grapiness. The LL wine had a tarter, more austere finish. The HL and HH wines tended to be leafier and more austere, higher in acidity and more tart. Literally, the proof was in the wine. It was there to taste. It was an exciting culmination of all the overwhelming data and input. The taste of the fruity, tart Sauvignon Blancs brought it to an immediate and powerful conclusion. Clearly, Wample was excited. And the results of the work were exciting. The wine growers, faced with another year of drought, could use his study to better manage limited water resources by using less water at the beginning of the season and slightly more at the end to help the vine survive potential cold weather conditions. Beyond the drought conditions loom even greater water-use issues such as draw- downs of the Columbia and Snake Rivers, and more restricted water usages in the future are going to make Wample's work much more elisimportant. ■ sa MARCH/APRIL 1991 PWV GRAPEGROWING

techniques for vineyard water management • By Charles Krauter, Keith Striegler A tensiometer indicates when the sup- Monitoring plant water stress California State University, Fresno ply of water is almost gone. However, A device that measures vine water stress some experimentation may be necessary is potentially the best method of water to determine the amount of water re- management, since that is the element Irrigation is one of the most important quired to fill up the root zone. that irrigation is supposed to control. techniques in viticulture. Applying the Conductivity devices such as gypsum Water stress will occur at different soil right amount of water at the right time is blocks respond to the same soil moisture ' water contents, or evapotranspiration vital to the yield and quality of the grapes. conditions as tensiometers but they are rates, so management methods that rely Because water is increasingly scarce and usually not as accurate in very moist soil. on these factors may at times be in error. expensive, improving the efficiency of its A tensiometer can only read soil mois- When a vine is water-stressed, its growth application is becoming an important ture when the root zone is fairly moist. It rate will be reduced, and that will often economic factor. goes off-scale and fails before the soil decrease yield. There may be benefits to There are three basic methods of man- moisture is completely used up. The Mildly stressing the vine at some growth aging vineyard irrigation. Each has ad- range of soil moisture at which the con- stages but those benefits can only be vantages and disadvantages, but each is ductivity block is most accurate is at consistejttly achieved if the stress level best applied to a particular situation. about the point where the tensiometer can be measured and the irrigations pre- The first and oldest method is soil mois- quits. cisely controlled. ture monitoring. If used properly, instru- I Most grape vines will begin to stress Unfortunately, most of the devices that ments such as tensiometers, gypsum when the soil water content is still in the detect water stress in the vine are expen- blocks, and neutron probes can provide tensiometer's range of measurement, so sive, delicate research instruments, such an accurate measurement of the amount they are a good choice for viticultural ap- as the porometer and the pressure cham- of water available in the vine's root zone. plications. Gypsum blocks are more ber, that may only work under certain A second method is direct measurement often used for field crops or where the conditions. They subject the leaf to me- of plant water stress. This is the newest manager wishes to dry the soil to a point chanical sensors in order to measure and potentially the most valuable if it can beyond the range of a tensiometer. Some changes in leaf water potential. The pres- be developed for commercial use. new conductivity blocks have a better sure chamber is used for management of The third method -is water budgeting, range of sensitivity and since blocks are some field crops but no method has often called Et scheduling. Water budget- less vulnerable to damage during cul- been developed for its use in commercial ing jccertainly the easiest, but it is also tural practices and freezes, they may be viticulture. an ideal choice for vineyard moisture In the past several years, however, a the least direct. It can estimate both the technique using an infrared thermom- timing and amount of irrigation but one monitoring. The neutron probe is quite different in eter to measure leaf temperature has of the other methods usually will be re- _ been tried with some success. The tech- quired for verification. that it very accurately measures the nique is promising and research is cur- amount of soil moisture rather than the Soil moisture monitoring strength of the attraction holding the rently in progress to develop it for use in The use of instruments to monitor soil water in the soil. The probe can indicate commercial viticulture. moisture is similar to checking a fuel precisely how much water is in the soil, Unstressed vines transpire a great deal gauge in an automobile. They provide a but not the point at which the soil mois- from .their leaves in hot weather and quick, easily measured indication of the ture is low enough to cause water stress therefore reduce their temperature sig- amount of water remaining in the root in the vines. Different soils will hold dif- nificantly by evaporative cooling. Stressed zone of the vines. ferent amounts of water. vines cannot evaporate as much water, Devices like tensiometers and conduc- The user of a neutron probe must cali- so their leaves will not be cooled as much. tivity blocks are inexpensive and reliable brate the instrument for a particular soil It is possible to predict the temperature if used properly. They respond to the and root zone depth for the readings to of an unstressed leaf from measurements same force of attraction between water be of maximum value. Once that calibra- of the air temperature and humidity. The and soil particles that the root must over- tion has been done for the soil and crop, infrared thermometer can take the actual come to take up the water. Consequently, the neutron probe will provide the best temperature of a large number of vine they are best used for deciding when data for irrigation management if maxi- leaves in a short time and compare it to that force has become too high for suffi- mum accuracy is needed. Tensiometers the predicted leaf temperature. cient uptake and an irrigation is needed. and gypsum blocks, however, have been The ratio of the predicted, unstressed These instruments are not as useful for successfully used for decades and will leaf temperature to the actual measured measuring the amount of water that often provide adequate information at a leaf temperature can be expressed as a needs to be applied. substantially rower cost. number called the Crop Water Stress In- dex (CWSI). If theza leaves are act ally as

cool as the predicted value, the CWSI Water Budgeting-- The Et from CIMIS must then be cor- will be 0 for the unstressed vines. If it is The third basic method of water man- rected for the particular growth charac- stressed, the CWSI will be more than 0; agement is water budgeting, often called teristics of a vineyard to get the daily the higher the level of stress, the higher 'Et scheduling'. It is essentially an appli- water use of the vines being managed. the number. cation of accounting with water instead The manager must know the vineyard This daily crop Et is then deducted from of money. The manager tracks irrigations, the estimated water supply in the root well enough to be able to determine the water stored in the root zone, and evapo- reason for a stress detected by the CWSI transpiration just as an accountant tracks zone. When an irrigation is called for, the amount to be applied is the total of the method. Insect damage and disease can income, bank balance, and expenses. daily Et's since the last irrigation. result in plant stress that irrigation can- Et scheduling is best done on a small This process can be used in its simplest not relieve. When the problem is actually computer with programs very much like form to make rough estimates of the ir- water stress, it may not be controllable by the accounting systems available for rigation schedule, or it can use carefully better irrigation management. PC's. The manager estimates the amount measured inputs to make the estimates For example, on a hot or windy day, a of water in the root zone of the vine and more precise. Extra effort in correcting vine may be stressed to some degree then deducts the amount used each day the reference Et from the weather station even though the soil is filled with water. Extreme atmospheric conditions can by evapotranspiration. When the soil with crop and stress coefficients is the water has been depleted to the point best way to increase the accuracy of the draw more water out of the leaves than where an irrigation is needed, the amount water budget. the root system is capable of supplying. missing from the soil is applied in an ir- Since the CWSI should be measured in Conclusion rigation and the root zone account bal- The question of which of these three the middle of the day, this unavoidable ance is replenished. stress may often be apparent and the basic methods is best for vineyard water manager will have to be familiar enough The advantage of this method is speed management has no simple answer. They with the phenomenon to know that it and adaptability to computerization once can each be used effectively once the cannot be prevented. the system is set up with the initial infor- manager has properly set them up and Exceptionally cool temperatures or fog mation and estimates. The major prob- become experienced in their operation. can reduce the transpiration rate of the lem with the method is acquiring accur- None of them can deliver precise irriga- tion schedules immediately; they all re- vines to the point where the plant can ate initial information and making pre- get sufficient water from a relatively dry cise estimates of the water available to quire some fine-tuning, for a season or soil for those conditions. No stress will the vines and daily evapotranspiration. more, to reach maximum utility. be measurable on such a day, but the The total amount of water in the root One generalization that can be made is manager must be aware that when normal zone is not difficult to estimate, but the that the best management often combines temperatures return, the vines may sud- portion of that amount that the vine can two of the methods. Many professional denly be short of water. use without being stressed is not so easy consultants use the water budget to make The measurement of leaf temperature to calculate. estimates of the irrigation schedule and with an infrared thermometer can easily Usually, only 25% to 50% of the water then use soil moisture instruments to be in error unless -the instrument is care- in the root zone is readily available, and regularly check the accuracy of the Et fully aimed to read only sunlit leaves. If an irrigation should take place when that program. surfaces such as the sky, soil, or wood are amount has been taken up by the vine. The computer-based Et schedule is easy One of the more difficult decisions to be to generate and the soil instruments need included in the field of view of the sensor, only to be read large errors can result. Correct technique made is the selection of this 'allowable once or twice a week to can provide accurate readings, allowing depletion' of the vine root zone. The verify it. As this plant stress measure- the CWSI to be properly calculated. other difficult estimation the manager ment method becomes more established, The advantage of the method is its ability must make is deciding just how much it could replace soil moisture monitoring to quickly measure conditions over a large water the vine used each day, i.e., the in the hierachy of water management area. It is the only device than can provide evapotranspiration or Et. methods. ■ the manager with sufficient, real time, The Et of the vines depends on both the water stress information to allow daily weather conditions for that day and the adjustments in the irrigation schedule. growth characteristics of the particular If an intentional or programmed stress vineyard. Temperature, humidity, wind, level is desired, a drip system can be and sunlight can be used in a formula to used to vary the application by reducing calculate a generic value called the ref- the irrigation when the CWSI is too low erence Et. and increasing it when the CWSI exceeds This process is complex and expensive the desired level. This is the only way that for an individual grower, but there is a changes in water stress due to changes in _ network of weather stations operated by growth stage or evapotranspiration can the state of California called alvIIS. These be taken into account. stations are located in all major growing Direct measurement of plant water areas and can be used to obtain a refer- stress is, at the moment, the most dif- ence Et for that region. (The Et informa- ficult method, but it could become the tion may also be available from private or most useful once proper techniques and public sources in other states, or in re- management interpretations have been gions in California not served by CIMIS. established. Data from these other sources may have to bet onverted to the proper Et form by the user.) OSA fin59 9/7 2 DRIP IRRIGATION

The authors are Albert W. Marsh, Extension Irrigation and Soils Specialist; Roy L. Branson, Extension Soils and Water Specialist, Riverside; C. Don Gustafson, Farm Advisor, San Diego County; and Sterling Davis, Agricultural Engineer, ARS, USDA, Riverside

What is drip irrigation control station for the system, where water is measured, filtered, treated with fertilizer in Drip irrigation is the frequent slow application solution, and regulated as to pressure and timing of water to soil through mechanical devices of application. called emitters located at selected points along water delivery lines. The application rate must be slow enough so that the flow of water across Why the great interest the soil surface is limited, and runoff in the Drip irrigation has created wide interest in a usual sense does not occur; most of the move- short time in spite of a small amount of experi- ment of water to wet the soil between emitters ence, information, and development. The main occurs by capillarity beneath the soil surface. factor behind this interest has been the potential of drip irrigation to reduce operating costs. Early The volume of soil wetted in an orchard or field reports indicated that a grower could irrigate his is usually much less than that wetted by other crop with less than half the usual water con- methods of irrigation, varying from 10% for newly sumption and obtain greater yields. Labor costs planted permanent crops to as much as 50% for for irrigating could also be cut, since water some mature crops. The amount of soil wetted applied by drip irrigation presumably does not depends on soil characteristics and the number have to be tended, but merely regulated by turn- of emitters. The number of emitters used ranges ing valves. Many growers, faced with scarcity from less than one per plant for row crops, to and high prices for both water and labor, imme- eight or more for large trees. diately embraced the prospect that drip irrigation would be financially beneficial. Drip irrigation systems also offer the opportunity to inject How is it done fertilizers into the irrigation water, avoiding The emitter, the key element in a system, pro- labor requirement for ground application. vides the slow flow needed. Most emitters are manufactured to provide a fixed rate of output with a specified water pressure. A few have Other advantages adjustable rates. Rates available usually range from 1/, to 2 gallons per hour (gph). One gph is • Since drip rates are slow, main line and the most common. lateral line sizes can be smaller than those for sprinkler or surface irrigation. Most emitters provide a point source of water, usually placed directly on the soil surface; some • Because much of the surface soil never be- are buried at shallow depth. Others provide a comes wet, orchard operations are not inter- line source of water from a tube having perfo- rupted. Weed growth is reduced so control rated or porous walls. This type is usually efforts are reduced. buried. • With row crops on beds, the furrows in which pickers walk remain relatively dr y and provide The emitters are connected to or are part of a firm footing. small diameter ( 3/s to 3/4 inch) plastic lateral line. The laterals generally lie on the soil surface • Frequent irrigations maintain a soi I moi sture but may be buried at shallow depth for protection. condition that does not fluctuate between wet They connect to a buried plastic main line that and dry extremes and keeps most of the soil receives water from a head. The head is the well aerated.

The University of California's Agricultural Extension Programs are available to all, without regard to race, color, or national origin. ONE-SHEET ANSWERS Ul AGRICULTURAL EXTENSION UNIVERSITY OF CALIFORNIA

1a-operative,0 Exten s io n wor k i n Agriculture and Home Economics, College of Agriculture, University of California, and United States Department of Agriultur• aerating. Distributed In furtherance of the Acts of Congress of May 8, and June 30, 1914. George B. Alcorn, Director, California Agricultural Extension Servico. • Avoidance of intermittent drying permits use of more saline water than can be used with other methods of irrigation.

Potential problems

Because the emitter outlets through which water must flow are very small, they can become plugged by particles of mineral or organic matter carried in the water. Dissolved salts can also crystallize around the external perimeter of the orifices reducing the size of opening. These re- strictions may reduce the emission rate, upset the uniformity of distribution of irrigation water, and cause plant damage before plugging is de- tected.

Most emitters operate at low pressures, 3 to 20 psi. If the field slopes steeply the nozzle pres- Kodents are known to chew polyethylene laterals. sure and discharge during irrigation may differ Rodent control or use of PVC laterals are pos- up to 50% from that intended, and the lines drain sible solutions. through lower emitters after shut off. Some plants would receive too much, others too little water. Operational requirements

Some soils may not have sufficient infiltration • Cleaning the water is essential. Most failures capacity to absorb water at the usual discharge observed are caused by inadequate filtering. rate without runoff or undersirable ponding. At Multiple screens as fine as 200 mesh or sand one gph discharge, the soil must have in infiltra- filters should be used. tion capacity of 0.5 inch per hour to keep the pool of free water around the emitter from ex- • Irrigations must be frequent and light. ceeding 2 feet in diameter. Sandy soils are prob- • Duration of each irrigation must not be too ably best adapted to drip irrigation, especially lengthy, helping avoid local excessive wet- those with slight horizontal stratification. Such ness in soils lacking rapid permeability, and stratification is beneficial for drip irrigation minimizing algae growth in laterals. because it promotes lateral water movement and wets a greater volume of soil. Experience has • Amount of water applied should be based on shown that medium textured soils usually per- measured or carefully observed soil-water form well, but some fine textured soils have conditions. created problems. • Though water emission rates are small, lateral lines must be designed with adequate capac- Salts tend to concentrate at the soil surface and ities to carry the maximum expected flow rate also at the perimeter of the soil volume wetted with little or no loss of pressure. Since lateral by each emitter. Since light rains will leach lines are generally of uniformly small diam- surface accumulated salts into the root zone, eter, their length should not exceed 330 to irrigations should continue on schedule until 400 feet. Additional main lines are preferable substantial rain has fallen. Drying of the soil to excessive lateral lengths. between irrigations may cause a reverse move- ment of soil water resulting in the transfer of • If flushing type emitters are used, lateral salt from the perimeter back toward the emitter. lines must be designed to carry the larger initial flow rate needed for flushing.

Water movement must always be away from the • Pressure regulators are necessary on sloping emitter to avoid salt damage. land. The laterals should be laid as level as possible. The foraging ability of the roots for nutrients and water is limited to the small volume of soil • Phosphate fertilizers should not be applied wetted. Should uncontrolled events cause sus- through a drip irrigation system; phosphate pension of water and fertilizer supplies, damage reacts with calcium in irrigation waters, form- to the cropcould occur rather qUickly. ing a precipitate that can clog emitters. xversity of California • s Agricultural Extension Programs are available to all, without regard to race, color, religion, sex, or national origi0 . __ FACTORS TO BE CONSIDERED IN THE SELECTION & APPLICATION OF IRRIGATION FILTERS

1. Introduction to irrigation filtration. The function of an irrigation filter is to remove suspended solids from irrigation water; to make th'at water suitable for low volume drip-trickle or sprinkler system application. The nature or type of solids or particulate in the irrigation source water is a determinate factor in selecting the type of irrigation filter to use. Particulate or suspended solids in irrigation water consists of organic and inorganic matter. These are considered physical contaminants and are easily handled with proper filtration. The particulate would be items like algae, weed seed, snails, moss, etc. an certain forms of bacteria, i.e. anything that is or was alive. The inorganic matter would be the range of sand, soil, silt particles, minerals and some chemical contaminates that appear in a solid mineral form. In addition to the organic and inorganic suspended solids, some irrigation water also contains (in solution) chemical and/or biological properties that through the injection of fertilizer or other chemicals can be converted to suspended solids. These are usually referred to as precipitates or precipitated matter. If these are precipitated prior to filtration, they can be effectively handled. The selection of the proper irrigation filter type and size is dependent on several important factors: a) The type, size and concentration of contamination in the irrigation source water. b) The quality requirement for the filtered water. c) The flow rate or peak water requirement. d) An initial investment cost analysis.‘

2. Definition of filter equipment and recommended application. True filtration equipment is classed into two basic types. a) Sand media filters. b) Screen filters. In addition, centrifugal sand separators are available for certain limited applications in removal of heavy or larger inorganic particles from water, however, they are not effective in removal of organic or fine inorganic particulate. Sand separators are not applicable to low pressure systems since the pressure loss through a separator is very high.

A. Sand Media Filters: These filters are ideally suited for filtering water with either organic or inorganic particulate. Sand media filters are the proper selection for filtering source water that is heavy with organic matter. Sand media filters have the ability to entrap and hold large quantities of contaminate. This type of filter uses a bed of sand as the filter media. The size and type of sand can be specified to achieve the desired water quality. These filters are cleaned by reversing the water flow through the bed, expanding the media allowing it to release and eliminate the trapped particulate out through the backwash line. The diagram in fig. A shows the flow and backwash action in a vertical tank filter system. Horizontal type sand media filters employ the same basic principles, however on high rate filtration applications they are not as effective as vertical filtration units. Horizontal filtration is generally recommended for gravity flow applications with flow rates of 10GPM ft2 or less.

Figure A

BACK FLUSH

- OUTLET - THE FILTERING PROCESS THE BACKWASH PROCESS

One of the most important functions of the sand media filter is its ability to properly backwash and clean the particulate from the sand bed. Various methods for water distribution are used to accomplish this backwash function, i.e. slotted pvc lateral pipes, wedge wire tube distribution, etc. These methods all use a loose gravel pack around the water distribution system to support the sand bed. During backwash and while the sand is being expanded for cleaning, the loose gravel is also dislodged and a sand- gravel mixing occurs. After backwash some sand is co-mingled with the gravel and will pass out through the system or will wedge against or in the slots of the water distribution tubes causing a blockage. The unique water distribution system used in the Free Flow filter's ceramic sand bed support structure, provides the most effective backwash of any filter in the industry. This support structure eliminates the use of loose gravel pack and provides a barrier so that sand does not pass through the system. 7:1 The Free Flow steel, epoxy coated screen filter employs a vortex- centrifugal water flow to separate the heavier particulate and collect this material in a bottom reservoir where it can be periodically flushed away. This filter further provides fine filtration through a screen mesh. This screen filter is extremely effective for filtering water that is heavy to inorganic particulate. Although a variety of screen filters are available in a multitude of shapes, sizes and materials, the most popular irrigation screen filter is the Free Flow Thru Flush screen filter. These stainless'steel filters employ a polymeric screen mesh (available in 30 to 200 mesh) for fine filtration or may be used with a stainless steel perforated screen for sprinkler system filtration. This line of filters is quickly cleaned by opening the Thru Flush valve to allow the system water to wash the accumulated particulate from the screen and out through the Thru Flush port. The screen does not have to be removed for cleaning as with most other screen filters. The easy field replaceable screen mesh allows a change in the mesh size if different filtered water quality is desired.

VALVE

77° Prog]nl

INLET OUTLET Filtration Mode Flow enters the barrel, passes through the screen, depositing debris upon the inside of the supported mesh.

VALVE

=M.! •■••••• -am fiE[THE 11-",=-1 THRU FLUSH

INLET OUTLET

Thru Flush Mode The opening of the Thru Flush valve creates a high velocity flow along the inner walls of the mesh screen and out the Thru Flush port, affording maximum cleaning action. Usually screen material is made of stainless steel or a polymeric mesh. While stainless steel screens are stronger the flexibility of a polymeric screen aids in the cleaning process. 23l Sand media filters are generally employed in multiple tank sets that provide for filtered water backwash. This greatly reduces the chance for field emitter, tube and line contamination. Backwashing the filters is the process by which clean water flows upward through the bed, lifting and expanding the media, allowing it to release the collected contaminate. The contaminate is then carried away with the backwash water. Excessive backwash flow rates will expand the media to the point that the media itself is expelled out of the tank. Insufficient backwash flow will not expand the media enough to purge all the entrapped contaminate. This could result in a residual pressure loss through the bed, even after backwash. To achieve maximum filter performance, the back- wash flow must be properly adjusted. Although the amount of water required to backwash the filter bed is small compared to the amount of water filtered, it is discharged at a high rate for a short period. Provisions should be made to drain away, store, or otherwise dispose of the dirty backwash water. The backwash line should not be connected to a transfer pressure line and should be discharged to atmosphere. The G.P.M. Flow capability through any sand media filter is determined by the square foot media surface area times the given flow rate. Example: a 36" diameter set of 2 filter tanks has a square foot media surface area of 14.2 square feet. With a given flow rate of 25 GPM per square foot, the 36-2 filter can be operated at 355 GPM (14.2 ft.2 x 25 GPM flow rate = 355 GPM). A maximum flow rate of 25 GPM is recommended for the average irrigation source water, however, in cleaner than average water, rates up to 30 GPM have been successfully applied. (A subsequent section on filter sizing should be referred to prior to filter size determination). The same factors are applicable to other size filters from a 88 GPM (18"-2) filter system through the 1800 GPM (48"-6) filter system. It should be emphasized here that the minimum water available to the filters must be a quantity adequate to backflush the filters. B. Screen Filters: This type of filter is recommended primarily for filtering water with inorganic particulate. The screen filter is not effective with water containing significant amounts of organic contamination. Unlike sand filters, screens do not have the ability to trap and hold large amounts of organic particulate without restricting the flow through the filters. There are many varieties and design of screen filtration available. Bar screens employ a flat screen surface the water passes over and the particulate is caught in the screen and occasionally flushed off or the screen removed for cleaning. These type of screens are usually employed in gravity filtration applications. Continual cleaning screens have a pressure water flow constantly passing back through the screen to flush away the particulate from the screen, although effective, these are very water wasteful and have mechanical parts that can and do create maintenance problems. 13 It should be again emphasized that screen filters are most effective on inorganic contaminant. Large amounts of organic particulate tend to quickly block the screen, requiring frequent flushing or cleaning.

3. Proper Sizing of Irrigation Filters: All filters are designed and rated to provide specific maximum rated GPM flow of filtered water with average source water conditions. However, if the condition of the source water has a heavier than normal amount of particulate, additional filter surface area will be required to provide the same quantity and quality of filtered water. Thus, a larger filtering system should be specified to provide extra filtration capability in heavily contaminated water. Seasonal water quality fluctuation should also be considered when sizing irrigation filtration. Example: As previously discussed, a 36"-2 tank sand media filter is rated with average water conditions at 355 GPM. If the source water condition is or could become heavier in particulate, it would be advisable to select a larger size filter to provide more filter surface area. In this example a 48"-2 would be selected and would provide quality filtered water without excessive backwash. (This is the same as reducing the flow rate per square foot of filter surface area.) The same principle holds true in the sizing of a screen filter. If a recommended flow rate for a filter is 400 GPM and the requirements of filtered water is 400 GPM and the water is heavy to particulate, then a larger screen filter system should be selected. Most quality filtration products are designed so that if the filtered water requirements increase at a later date, additional units can be added to the filter system to increase the filtered water capability. A 48"-2 sand media filter system can be easily increased to a 48"-3 tank system; a single 400 GPM screen filter can become a two screen system, etc.

4. Sand or Mesh Media Size Selection: The filtered water quality is achieved by the filter media used. Too coarse screen or sand size will lead to clogging or plugging of the irrigation system and too fine filtration media will cause unnecessary, rapid and excessive cleaning of the filters. The type or size of the sprinkler heads, emitter nozzles or drip tubing used in the irrigation system should be determined and filter media sized for that application. Most quality filters are designed so that the media size can be changed, if at a later date, a change in the irrigation system would require a different filtered water quality. The chart in fig. C shows the relationship between sand sizes and the equivalent screen mesh sizes. Screens are classified by the size opening and the opening is defined by a mesh number. The mesh number refers to the number of openings per inch. The relationship between sand size, pore size, mesh number size are also shown in fig. C. 233 Filter sand is classified by two factors - mean effective size and uniformity coefficient. The effective size is the measure of the minimum sand size in that grade while uniformity coeffecient is the range of sand sizes within that grade. A more complete definition of these terms is given in fig. C.

Fig. C. Sand size, pore diameter, v/s screen mesh.

Sand Effective Approximate U.S. Designation Sand Size Pore Diameter Screen Mesh Number inches mm inches mm Designation 8 .059 1.50 .0084 .214 70 11 .031 .78 .0044 .111 140 20 .018 .46 .0026 .066 230

Definitions: (Courtesy American Water Works Association - Standards for Filtering Material). Effective Sand Size: That size opening that will just pass 10% of a rep- resentative sample of sand. An effective size of .78 mm means that 10% of the sample is finer than .78 mm. Uniformity Coefficient: A ratio of the size opening that will just pass 60% of a representative sample of sand divided by that opening that will just pass 10% of the same sample. (A uniformity coeffecient close to 1.5 is considered good for irrigation filter sand grades.) Sharp, crushed media is recommended for sand filter use. Two basic materials are used -sharp, crushed silica sand or sharp, crushed granite. 5. Manual or Automatic Operation: Most irrigation sand media and screen filters are available for either manual or automatic operation. The manual flushing operation is activated by hand opening a flush valve or removing the screen and cleaning when a specified pressure differential is indicated on the pressure gauges. Regularly scheduled backwash or screen cleaning is necessary to assure proper operation. Free Flow automatic systems provide for unattended flushing of the filters on a pre-scheduled time interval basis, and in addition include an automatic pressure differential override safety circuit. One of the advantages of an automatic system is that the filters are assured of being cleaned on a scheduled basis. However, should the source water quality vary and pressure differential develop prior to the scheduled flushing time, the pressure differential circuit will activate a flushing cycle. The initial investment in automation can be compared to the repetitive labor cost of manual flushing, with additional consideration given fox the economical operation and safety that is provided by automation. 234 Most new filter controllers for automatic filter systems are designed with digital solid state components and are available for either 110 volt A.C. electrical input or for operation with a 12 volt D.C. power source. In addition, solar power collector units are available as an alternative power source.

Summary: The selection and application of the proper filtration equipment is vital to the success of a modern irrigation system. John Ribble of the University of California sums it up in his paper on filtration where he states in the final paragraph: "The goal in selecting a filter is to achieve the necessary filtration and maximize efficiency of operation while minimizing cost, maintenance time, labor and operator inconvenience. To reach this goal certain guidelines must be established: a. The size of the irrigation system (flow rate in gallons per minute, pressure, and volume of water required) — the capacity of the filter should exceed the demand of the system. b. The physical, chemical and biological quality of the irrigation water to be used. The size and quantity of suspended solids to be removed; probabilities of chemical and/or biological clogging; stability of water quality with time. c. The complexity of the- filter unit — what problems would be involved with cleaning or replacing the filter. d. Availability of labor for cleaning and maintenance — for larger systems automatic flushing is generally used. e. Location of the filter unit and disposition of the backwash and rinse water. f. Flexibility of the filtration system — capability of enlargement or modification if it becomes desirable."

WATER MANAGEMENT PRODUCTS DIVISION rardney P.O. BOX 1566, CORONA, CA 91720 PHONE (714) 687-3901 235