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Site Evaluation and Soil Physical Modification

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Site Evaluation and Soil Physical Modification the orchard SITE EVALUATION AND SOIL PHYSICAL MODIFICATION Allan Fulton, Blake Sanden and John Edstrom istachios are similar to other nut crops in 1) Reduced physical barriers to drainage and P that high yields and pistachio quality are root development. best achieved on deep, uniform loam soils. 2) Increased uniformity of water infiltration These soils provide the optimal combination of and water-holding characteristics. permeability with sufficient water-holding 3) Improved leaching of excess salts. capacity and root zone aeration. However, 4) More uniform and increased vigor in young acquiring these deep alluvial soils are more orchards and less time to achieve full expensive due to their limited availability, so production potential. many new orchards are being developed on soils with limitations. Surface and subsoil variability Orchards with soils that vary from sands to Site evaluation has two major clay texture are subject to variable water stress objectives: across the orchard because of different water- 1. Evaluate the quality of the soil and water holding capacities of the soils. Layers of with respect to acceptable salinity and different soils in the rootzone can cause water fertility for long-term profitable logging by slowing water movement through production. the root zone and creating temporarily 2. Evaluate any soil physical limitations with saturated soil layers. These injure roots by respect to layering and drainage that may depriving them of oxygen and enhancing restrict root development. conditions that favor root diseases. Some subsoil layers can form physical barriers to Later chapters in this manual address roots that simply cannot grow through hard, fertility and salinity management. This chapter dense, or compacted layers. The result is discusses soil physical limitations, pre-plant nonuniform orchard growth and production, site evaluation recommendations, choices especially under surface irrigation where among irrigation methods, land leveling, and infiltration rates can vary considerably from selecting effective tillage methods. The first one area to the next. goal of a good site physical evaluation is to identify any potential limitations and if Soil survey data modification is truly necessary. Avoid The best place to begin your evaluation is with expensive deep tillage operations if they are not the USDA Natural Resource Conservation needed. The second goal is to take corrective Service soil surveys. There are 170 published action before planting when it is most surveys for California alone – starting with the feasible. Correcting a physical soil limitation first Fresno County survey in 1900 to the most after orchard establishment is usually not recent Western Tulare County survey in 2003. nearly as effective. Many of these surveys are revisions of earlier surveys, changing and adding to earlier soil EVALUATING SOIL PHYSICAL series descriptions. The surveys published LIMITATIONS since 1970 have the best maps (Plate 4A.) and Evaluation and appropriate modification of soil series detail. orchard soils provides the following benefits: On-line access: Unfortunately, only a small number of these surveys are available 40 online. Use the following links to obtain modification, how to properly set up and use information: deep-tillage equipment, and when to what List of all California soil surveys: depth tillage is required. One alternative to http://www.soils.usda.gov/survey/printed_ backhoe pits is the use of a soil probe to pull surveys/california.html undisturbed soil cores for evaluation. Special Full surveys published online: equipment is required for this option if you http://www.ca.nrcs.usda.gov/mlra02/ want to examine the profile down to six feet • Colusa County, CA and it must be done by an experienced • Intermountain Area, CA agronomist/soil scientist who knows what to • Mendocino County, CA, Western Part look for. Using your farm backhoe or even • Napa County, CA renting one may be cheaper in the end and will • Santa Cruz County, CA be more revealing as the entire profile can be • Stanislaus County, CA, Western Part viewed at once. (See Plate 4B. for an example • Tulare County, CA, Western Part pit.) • Yolo County, CA As a rule of thumb, it is advisable to dig at For georeferenced spatial and tabular data least one backhoe pit per 20 acres. Where available for California (more difficult to possible, locate backhoe pits in areas of the access and requires use of GIS software): prospective orchard site that have a history of https://soildatamart.nrcs.usda.gov/County. desirable as well as poor growth, for aspx?State=CA comparison. For locating NRCS offices in the US: http://offices.sc.egov.usda.gov/locator/app Kimberlina For most areas it may be necessary to contact the local NRCS office and consult the area conservationist and a paper hard copy of the survey. Most current surveys are supposed to be online by 2008. Identifying physical limitations Lewkalb The soil survey, along with aerial images and Garces personal observation of row crops previously grown in the field is very useful for identifying “zones” that should be sampled and viewed Milham separately. Commercially available equipment (i.e. EM-38 and VERIS equipment) that use Figure 4a. Soil type variability and required electromagnetic or conductivity sensors and sampling areas for a 160 acre orchard development. global positioning systems technology can also map soil variability. When properly calibrated, Estimating site evaluation costs the sensors detect changes in soil salinity and The cost of evaluating the physical soil major differences in water holding capacity. characteristics of a prospective orchard site and Figure 4a illustrates the potential variation one pulling soil samples will range from $200 to might find in a possible 160 acre orchard $1,200, depending on field size and variability development in Western Kern County. of soil types. This will be about 0.5% of your A thorough site evaluation uses a series of eventual development cost; far less than the backhoe pits in the different zones. Observation cost of establishing an orchard at a poor site. A pits clearly show the number and types of soil backhoe service can be contracted for about layers, the depth of the layers, and the $60 per hour, and the work can be completed variability of the subsoil throughout the within a day. Laboratory costs for soil and orchard site. This information can help water analyses, depending on the number, will determine the most economical method of soil run $40 to $70 per sample. Samples should be 41 taken in a “composite” manner for multiple Table 1. San Joaquin Valley soil series depths down to at leas 4 feet. See the chapter having physical soil limitations but that are on Managing Salinity, Soil and Water commonly considered for pistachio orchards Amendments for a more detailed discussion on Developed clay subsoil types sampling and interpreting analyses. Cemented Stratified Moderate Claypan hardpan Soil series evaluation guidelines Eastside San Joaquin Valley soils Extensive soil modification is not always Cajon Borden Cometa Academy necessary to prepare an orchard site for Chino Chiralar Corning Dinuba planting. Some soils are naturally deep and relatively uniform in soil texture and structure, Foster Pond Modesto Exeter and do not require deed tillage. However, other Grangeville Ramona Montpellier Fresno soils are layered and may need modification. Hanford Ryer Waukena Lewis Four types of physical soil limitations may be San observed while conducting backhoe site Kimberlina Snelling Milham Joaquin evaluations: (1) stratified soils, (2) claypan Nord Complex Whitney soils, (3) hardpan soils, and (4) plowpans. Visalia Table 1 summarizes some common soil series in the San Joaquin Valley known to have Westside San Joaquin Valley soils physical soil limitations. Camarillo Avenal Herdlyn Dinuba Stratified soils have layers with abrupt Columbia Twisselman Olcott changes in soil texture beneath the surface (Plate Mocho Pleasanton Positas 4B, Caliche layer and Plate 4C, clay over sandy Panoche Rincon Solano loam). The layers interfere with the uniform Westhaven Rossi Waukena drainage of water, causing zones of poor aeration Vernalis Garces Buttonwillow that may restrict root growth. Correcting layered soils requires mixing the soil layers. Plowpans can be found in some orchard Claypan soils have a concentrated clay sites. Plowpans are the result of tilling a soil at layer that restricts water movement downward, the same depth repeatedly. A soil with a thus restricting aeration and root growth in the plowpan does not necessarily have different subsoil. Clay layers can start abruptly at a textural layers like those of stratified, claypan, depth of 12 to 24 inches below the surface, or hardpan soils. Instead, plowpans are usually with the clay most concentrated in the upper shallow (10-18 inches below the surface) and half of the pan. The lower half gradually require only fracturing, rather than mixing, to changes into a clay loam to loam-textured soil. correct the problem. Modification designed to mix the clay layer with the rest of the soil profile will result in IRRIGATION SYSTEMS & GRADE more uniform water penetration, reduce LIMITATIONS saturation in the upper rootzone and promote Selecting an irrigation method extensive tree root growth. Selection and design of the irrigation system Hardpan soils are similar to claypans, will be influenced by site topography and soil except the soil particles are glued together by types. It will also be the main driver behind hard mineral matter that will not soften, even final land leveling and tillage requirements. when wet. The hardened layer is usually an Properly designed and managed absolute barrier to root growth and water microsprinkler, surface drip, subsurface drip, percolation. Modification of hardpan soils and sprinkler systems help minimize physical requires fracturing and breaking rather than soil limitations more than surface irrigation mixing. systems. 42 Cost considerations: The advantage of 4. Grade to uniform slopes to avoid low and choosing a flood or furrow irrigation system high spots. over a pressurized irrigation system is reduced 5.
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