Technical manual for “Fertigation manual: Open-field crops and date palm"
Technical manual for
Fertigation manual: Open-field crops and date palm
Naeim Mazaherieh Biju George Arash Nejatian Azaiez Ouled Belgacem
2018
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Technical manual for “Fertigation manual: Open-field crops and date palm"
Contents 1. INTRODUCTION ...... 3 ADVANTAGES OF FERTIGATION ...... 3 2. DETERMINING CROP WATER USE ...... 4 3. PLANT NUTRIENT REQUIREMENTS ...... 8 THE UPTAKE PROCESS ...... 9 4. FERTIGATION MANAGEMENTS ...... 10 THE TARGET YIELD AND CROP NUTRIENTS REQUIREMENTS ...... 12 5. FERTILIZERS MANAGEMENT ...... 13 BASIC MIXING RULES ...... 13 PRECIPITATION ...... 15 SOIL- NUTRIENT SAFETY MARGINS ...... 15 NUTRIENT SOURCES (FERTILIZERS) ...... 15 SALT INDEX ...... 15 FERTILIZERS PROPERTIES FOR FERTIGATION ...... 16 APPLYING THE RIGHT AMOUNTS OF FERTILIZER ...... 16 6. SETTING FERTIGATION SYSTEM ...... 17 SELECTING AN INJECTOR ...... 17 6.1.1. Venturi Bypass ...... 17 6.1.2. Metering Pumps ...... 18 6.1.3. Hydraulic Units ...... 18 .6.1.4 Conventional flow by-pass tank ...... 19 7. FERTIGATION UNDER SALINE CONDITIONS ...... 19 ELEVATED SALT LEVELS ...... 20 NUTRIENT INTERACTIONS ...... 20 NUTRIENT UPTAKE RATES AND MOBILITY ...... 20 8. FERTILIZERS APPLICATION ...... 21 SOLUBILITY ...... 21 ACIDITY ...... 24 9. SOIL TESTING ...... 26 ORGANIC MATTER ...... 27 DETERMINING NUTRIENT REQUIREMENTS ...... 27 SOIL CHEMICAL ANALYSIS AS A TOOL FOR EVALUATING NUTRIENT AVAILABILITY...... 27 9.3.1. Soil sampling and analysis ...... 28 9.3.2. Depth of soil sampling ...... 28 9.3.3. Method of soil sampling ...... 28 9.3.4. Interaction of soil analysis results ...... 29 10. DATE PALM FERTIGATION AND FERTILIZATION APPLICATIONS ...... 30 FERTIGATION CALCULATIONS ...... 31 11. REFERENCES ...... 35
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Technical manual for “Fertigation manual: Open-field crops and date palm"
1. Introduction Fertigation is known as the process of application of nutrients through irrigation systems in certain fixed concentrations according to the actual crops needs from irrigation water and nutrients at the different plant growth stages. This is done through the injection of fertilizers directly into the irrigation network to reach the level of humidity and a constant nutrients concentration in the root zone region.
The correct design of the irrigation network is the most important step for applying fertigation technology to ensure high efficiency in the distribution of fertilizer in the root zone region as well as good management and maintenance of the irrigation network operations and injectors fertilizing periodically and regularly is essential to ensure its work efficiently. Advantages of fertigation Nutrient requirement according to crop stages (tea spoon feeding). More uniform distribution and closer to root system. Better availability of nutrients to plants. Nutrient uptake increases. Reduced losses of nutrients by leaching. Preventing damages to roots. Less costly application labor. Less soil compaction.
Reduced weed population.
Application flexibility (time, weather, soil).
Disadvantages The system needs clean water (without solid particles) that may clog the emitters. (Filtration) Knowledge of the chemical composition of water is important to avoid precipitation with the added fertilizers. Sometimes pretreatment is necessary. (Filtration) The system needs equipment's which some of them are expensive. Not all type of fertilizers are suitable for fertigation.
What are the things needed to ensure good management of fertigation?
Determine the crop water requirements. Good and proper design of the irrigation system.
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Technical manual for “Fertigation manual: Open-field crops and date palm"
Use non-corrosion materials equipment's in fertigation system such as plastic and stainless steel Build up a fertigation program separately for each crop that meets its nutrients requirements according the growth sages. The total concentration of the elements in the main irrigation line must not exceed 5 g / l. Start the injection of fertilizers after sure that water filling all irrigation lines. Carry out maintenance of the fertigation system regularly and systematically
2. Determining Crop Water Use Crop water use is typically expressed in mm of water per day as ETc (evapotranspiration of the crop). It’s typically calculated by multiplying the reference evapotranspiration (ETo) rate, which is generated from daily local weather station data, by the crop coefficient (Kc), which is unique to the crop and the geography where it is grown.
The purpose of the Kc is to adjust generic weather information to reflect the specific crop being grown. Weather and crop coefficient data may be obtained from local government or university sources, or may be generated on the farm with proper equipment and research procedures. Table 1 represented the monthly average reference evapotranspiration (Eto) which estimated by using Penman Monteith equation basing on metrological data which collected from metrological weather station during 2013-2015 period at Fujairah (UAE).
Table 1. The monthly average Reference Evapotranspiration (Eto)
Mon May
Aug Sep Nov Dec
Feb Mar
Jan Jun
Apr Oct th Jul
(
mm/day
Eto
3,3 3,6 4,9 6,7 8.0 8.0 9.0 8,2 8,1 6,1 4,8 3,5
)
The tomato Crop Coefficient vs. Growth Stage graph shows how the crop coefficient changes according to the Growth Stage (Figure1).
Table 2 shows the average Kc values for the various crops during growth stages. In fact, the Kc is also dependent on the climate and, in particular, on the relative humidity and the wind speed. Table 3. Shows the crops stage interval for some vegetable crops.
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Technical manual for “Fertigation manual: Open-field crops and date palm"
Example 1 Estimation of actual crop evapotranspiration( Etc)
Calculate the daily tomato Etc and gross depth water applied (dg) during April using drip irrigation system with wetting percentage (WP) of 40% Data input Crop : Tomato Eto: from table 1=6,7 mm/day Kc: from Table2 & Table3 or Figure1=1,15 Irrigation efficiency = 0,86 ECw: salinity of irrigation water (dS/m)=5 dS/m maxECe = maximum soil extract salinity (dS/m) (Table 4 ) =8,4 dS/m Soil wetting percentage(WP) = 40 % Solution Etc = Eto*Kc = 7.71 mm/day Leaching requirement (LR)= Ecw/2ECe= 0.30 0.9*dn dg (1 LR)*Ea
0.9*7.71*0.4 dg 4.9mm 49m3/ ha (1 0.3)*0.81
Table 2. Values of the crop coefficient (Kc) for various crops and growth stages.
Crop Kcini Kcmid Kcend Crop height (m) Lettuce 1.00 0.95 0.3 Sweet peppers (bell) 1.05 0.9 0.7 Tomatoes 0.4 1.15 0.7-0.9 0.6 Cucumbers 0.6 1.00 0.75 0.3 Watermelon 0.4 1.00 0.75 0.4
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Technical manual for “Fertigation manual: Open-field crops and date palm"
Green beans 0.5 1.05 0.9 0.4 Peas 0.5 1.15 1.1 0.5 Wheat 0.7 1.15 0.25-0.4 1 Alfalfa 0.40 0.95 0.90 0.7 Berseem 0.40 1.15 0.85 0.6 Sudan grass hay 0.50 0.90 0.85 1.2 Grazing pasture 0.40 0.85-1.05 0.85 0.15-0.30 Turf grass 0.80 0.85 0.85 0.10 Date palm 0.90 0.95 0.95 8 Grapes 0.30 0.85 0.45 2 Citrus (70% canopy) 0.70 0.65 0.70 4 (Doorenbos and Pruitt, 1975)
Table 3. Values of the crop growth stage length (day) for various crops.
Crop Mid- Late Crop Initial Total dev season season Onion 20 45 20 10 95 Lettuce 25 35 30 10 100 Sweet peppers (bell) 30 40 110 30 210 Tomatoes 30 40 40 25 135 Cucumbers 25 35 50 20 130 Watermelon 10 20 20 30 80 Green beans 15 25 25 10 75 Peas 35 25 30 20 110 Wheat 20 50 60 30 160 Barley 20 50 60 30 160 Maize 25 40 45 30 140 Alfalfa 1st cutting cycle 10 20 20 10 60 Berseem 10 20 20 10 60 Sudan grass hay 25 25 15 10 75 Grapes 20 50 75 60 205 Citrus 60 90 120 95 365 (Doorenbos and Pruitt, 1975).
Table (4) shows crop tolerance and yield potential of selected crops as influenced by irrigation water salinity (ECw)
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Technical manual for “Fertigation manual: Open-field crops and date palm"
Table 4. Crop tolerance and potential yield of selected crops as influenced by irrigation water salinity.
Potential Yield 0% 100% 90% 75% 50% Vegetable crops “maximum”
ECw Squash, zucchini (courgette) 3.1 3.8 4.9 6.7 10 Beet, red 2.7 3.4 4.5 6.4 10 Squash, scallop 2.1 2.6 3.2 4.2 6.3 Broccoli 1.9 2.6 3.7 5.5 9.1 Tomato 1.7 2.3 3.4 5.0 8.4 Cucumber 1.7 2.2 2.9 4.2 6.8 Spinach 1.3 2.2 3.5 5.7 10 Celery 1.2 2.3 3.9 6.6 12 Cabbage 1.2 1.9 2.9 4.6 8.1 Potato 1.1 1.7 2.5 3.9 6.7 Corn, sweet (maize) 1.1 1.7 2.5 3.9 6.7 Sweet potato 1.0 1.6 2.5 4.0 7.1 Pepper 1.0 1.5 2.2 3.4 5.8 Lettuce 0.9 1.4 2.1 3.4 6.0 Radish 0.8 1.3 2.1 3.4 5.9 Onion 0.8 1.2 1.8 2.9 5.0 Carrot 0.7 1.1 1.9 3.0 5.4 Bean 0.7 1.0 1.5 2.4 4.2 FRUIT CROPS Date palm 2.7 4.5 7.3 12 21 Grapefruit 1.2 1.6 2.2 3.3 5.4 Orange 1.1 1.6 2.2 3.2 5.3 Grape 1.0 1.7 2.7 4.5 7.9
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Technical manual for “Fertigation manual: Open-field crops and date palm"
Adapted from Maas and Hoffman (1977) and Maas (1984). These data should only serve as a guide to relative tolerances among crops. Absolute tolerances vary depending upon climate, soil conditions and cultural practices.
Tomato Kc 1.4 1.2 1 0.8 Kc 0.6 0.4 0.2 Initial Crop Mid season
0 Late season
0 40 80 120 10 20 30 50 60 70 90 100 110 130 140 150
Growing season ( days after crop tranplanting)
Figure 1. Tomato crop coefficient under open field conditions
3. Plant nutrient requirements Some elements are known to be essential for plant growth and they can be divided into two groups:
• Macronutrients: these are nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg) and sulphur (S) and are required in relatively large amounts.
• Micronutrients (trace elements): these include iron (Fe), copper (Cu), manganese (Mn), zinc (Zn), boron (B), molybdenum (Mo) and chlorine (Cl), and are required in smaller amounts than the macronutrients. The names macro- and micro- nutrients do not refer to relative importance in plant nutrition; a deficiency of any one of these elements can limit growth and result in decreased yield. It is therefore important to ensure that there is an optimum supply of all nutrients – if a plant is seriously deficient in, for example, potassium it will not be able to utilize fully any added nitrogen and reach its full potential yield and any unutilized nitrogen may be lost from the field.
Soil and crop analysis reports usually show elemental forms for example mg P/kg or mg K/l. Oxide or elemental forms are used in this Manual according to context. Achieving the right timing of nutrient application is as important as applying the correct amount. Crop demand varies throughout the season and is greatest when a crop is growing quickly. Rapid development of leaves and roots during the early stages of plant growth is crucial to reach the optimum yield at harvest, and an adequate supply of all nutrients must be available
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Technical manual for “Fertigation manual: Open-field crops and date palm"
during this time. Excess application of nutrients, or application at the wrong time, can reduce crop quality and cause problems such as lodging of cereals or increases in foliar pathogens. Excessively large amounts of one nutrient in readily plant-available forms in the soil solution may also decrease the availability or uptake by the root of another nutrient. Other elements found in plants, which may not be essential for their growth include, cobalt (Co), nickel (Ni), selenium (Se), silicon (Si) and sodium (Na). Sodium has a positive effect on the growth of a few crops. Some elements, such as cobalt, iodine (I), nickel and selenium are important in animal nutrition. These are normally supplied to the animal via plants, and must consequently be available in the soil for uptake by plant roots. All these elements are taken up by plant roots from the supply in the soil solution (the water in the soil). They are absorbed in different forms, have different functions and mobility within the plant and hence also cause different deficiency, or very occasionally toxicity, effects and symptoms.
Integrated plant nutrient management Crops obtain nutrients from several sources:
Mineralization of soil organic matter (all nutrients) Deposition from the atmosphere (mainly nitrogen and Sulphur) Weathering of soil minerals (especially potash) Biological nitrogen fixation (legumes) Application of organic manures (all nutrients) Application of manufactured fertilizers (all nutrients) Other materials added to land e.g. soil conditioners
For good nutrient management, the total supply of a nutrient from all these sources must meet, but not exceed, crop requirement. Crop requirement varies with species (and sometimes variety of the crop), with yield potential (this in turn depends on soil properties, weather and water supply) and intended use). Nutrients should be applied in organic manures or in fertilizers only if the supply from other sources fails to meet crop need. Where nutrients are applied, the amounts should be just sufficient to bring the total supply to meet crop need.
In climatic conditions where there are frequent drought periods and on soils with a little water holding capacity, K plays an important role in counteracting water stress. K optimizing the water use by regulating the stomata. The Uptake Process The nutrient uptake is affected by soil pH and each nutrient element has different response to the pH conditions. The root hair surface contains organic compounds with excess negative charges neutralized by H+ ions and with organic compounds with excess positive charges neutralized by OH- ions.
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Technical manual for “Fertigation manual: Open-field crops and date palm"
The uptake process is based on exchange, for each positive charge that plant is adsorbing, H+ ions are released to the rhizosphere and vice versa for each negative charge, OH- ions are released to the rhizosphere.
Therefore, the pH monitoring especially in inert growth media can be done by changing the source of nitrogen.
- - Uptake of NO3 ions is involved by releasing of OH ions, which is involved in rising up of the + + pH. Uptake of NH4 ions is involved by releasing of H ions which causes dropping of the pH. Nutrient requirements and fertilizer dosage and timing fertigation system allows coordination of nutrient supply with changing demands of the growing crop. This requires a knowledge of the amount and rate of nutrient uptake by the crop in the growing cycle. Nutrient uptake at any one time depends on crop characteristics, the expected final yield, the nutrient content in the harvested crop and in the residual biomass, and environmental conditions: temperature, humidity and light. For crops grown in soil, the availability of the inherent nutrients has to be considered, in calculating the amount of nutrient to add. Also specific fertilizer recommendations for a crop have to be based on nutrient uptake measurements done under conditions as near as possible to those in which the crop is to be grown. In view of the above, it is obvious that only generalized fertilizer recommendations can be given for nutrient uptake by a specific crop and its different cultivars. However, fertigation is a practical technique and the grower has to optimize fertilizer use based on the best possible knowledge of nutrient uptake and complemented by leaf, irrigation and drainage water analyses and soil testing. 4. Fertigation managements The following should be known to write a suitable fertigation program:
Crop nutrients requirement (NW). Soluble nutrient in the irrigation water (SW). Available nutrients in the soil and the organic matter (ASO). Crop nutrient demand in the different crop growth stages.
The crop fertilizer demand= NW – ( SW+ASO)
Example 2 Cucumber crop is grown in sandy soil with bulk density of 1.6gm/cm3 and irrigated with 6000 m3 using drip irrigation system. Root depth is 40 cm, Soil analysis N =5 ppm, K=150 ppm, P= 40 ppm, Water analysis in ppm: N =10, P=4, K= 5. The expected yield production is 60 ton/ha. Two tons of organic matter (O.M) applied (O.M : analysis in Kg/ton) N =1, P=1, K= 3.1 Calculate the net crop nutrient requirement from N P K
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Technical manual for “Fertigation manual: Open-field crops and date palm"
Solution 1st step from Table 5 . Calculate the nutrient requirements to produce 60ton/ha cucumber N(kg/ha) = 60(ton/ha)*1.8(kg/ton) =108 kg/ha P(kg/ha) = 60(ton/ha) *0.6(kg/ton) = 48 kg/ha K(kg/ha) = 60(ton/ha) *2.5(kg/ton) = 150 kg/ha 2nd step The nutrient content (kg) in irrigation water N(kg/ha) = 6000m3 * (m3/ha) *10kg/1000(gm) =60 kg P(kg/ha) = 6000 (m3/ha) * 4(gm/m3) *1kg/1000(gm) =24 kg K(kg/ha) = 6000m3 * 5(gm/m3) *1kg/1000(gm) =30 kg 3rd step The nutrient content (kg) in O.M N(kg/m3) = 2 (ton) * 1 (kg/ton) =2 kg P(kg/ha) = 2 (ton) * 1 (kg/ton) =2 kg K(kg/ha) = 2 (ton) * 3.1 (kg/ton) =6.2 kg 4rth step The nutrient content (kg) in the soil Calculate the weight of soil of one hectare to a depth of 40 cm Weight of soil(tons/ha/0.4 m depth) = Field area(m2)*soil depth (m) *Bd(tons/m3 = 10000(m2)* 0.40(m)* 1.6(ton/m3) = 6400 tons Nutrient (kg/m3) = weight of soil(ton)*( soil nutrient content* safety margins)*soil occupied by root N(kg/ha) =6400(ton) * (10-0) (kg)N/1000(ton )*0.35 = 22.4 kg P(kg/ha) =6400(ton) *(35- 30) (kg)P/1000 (ton )*0.35 = 11.2 kg K(kg/ha) =6400(ton) * (130-100) (kg)K2O/1000 (ton )*0.35 =67.2 kg/ha 5th step Amount of N, P, K needed to be applied as fertilizer to produce 60 ton/ha of Cucumber crop are
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Technical manual for “Fertigation manual: Open-field crops and date palm"
The amount of fertilizer = Crop nutrient requirements - water nutrient content - soil nutrient content – organic matter nutrient content N (kg/ha) = 108- 60 – 22.4 - 2 = 23.6 kg/ha P (kg/ha) = 48 – 24 – 11.2 – 2 = 10.8 kg/ha K (kg/ha) = 150 – 30 – 67.2 – 6.2 = 46.6 kg/ha From Table 6. N, P, and K uptake efficiency by drip irrigation for sandy soil (0.75, 0.25 and 0.80, respectively) N = 23.6/0.75 = 31.47 kg/ha P = 10.8/0.25 = 43.2 kg/ha K = 46.6/0.80 = 58.25 kg/ha The target yield and crop nutrients requirements Before determine the crop nutrient requirements the farmer should make a disjoin on level of crop production to be achieved. Table 5 shows the crop nutrients requirements per each ton of yield produce.
Table 5. The nutrients required by selected crops to produce one ton of fruit.
Crop N P K Asparagus (hellion) 2.40 0.66 2.60 Cucumber 1.80 0.60 2.50 Eggplant 2.90 0.30 4.20 Lettuce 1.60 0.80 2.20 Onion 2.80 0.52 2.90 Pepper 2.10 0.50 3.50 Potato 5.00 0.35 5.00 Spinach 4.80 0.77 6.67 Tomato 3.0 0.60 3.50 Date palm 2.80 0.40 3.20 (Papadopoulos et al,.2000)
After identifying the target yield production, the crop nutrient requirement (NW) for a certain yield could be calculated as follows:
NW = expected yield (ton/ha)* crop consumption from nutrient (kg/ton)
In general, the higher the water use efficiency of a certain irrigation system the higher is the nutrient uptake efficiency. For a well-designed drip irrigation system and with good
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Technical manual for “Fertigation manual: Open-field crops and date palm"
scheduling of irrigation, depending on soil type, the potential N, P and K uptake efficiency ranges between 0.75-0.85, 0.25-0.35 and 0.80-0.90, respectively(Table 6).
Table 6. Fertilizer-N,P and K uptake efficiency (fraction) as influenced by the irrigation system and soil type
Soil Type Furrow Sprinkler Micro-irrigation N P K N P K N P K Clay 0.60 0.20 0.75 0.70 0.25 0.80 0.85 0.35 0.90 Medium 0.50 0.15 0.68 0.65 0.20 0.75 0.80 0.30 0.85 Sandy 0.40 0.10 0.60 0.60 0.15 0.70 0.75 0.25 0.80 (Papadopoulos et al, 2000) 5. Fertilizers Management Fertigation is the process of injecting one or more agricultural plant nutrients into irrigation water for application to the plant soil root zone, to meet a portion of a crop's fertilizer needs. A well designed drip irrigation system can provide an excellent partner for utilizing fertigation with commercial vegetable crops, especially when plastic mulch beds are also used.
Nitrogen and potassium fertilizers are the most common nutrients applied by fertigation to vegetable crops. Some formulations of phosphorus and micro-nutrients can also be used if compatible with the irrigation water (pH should be less than 6.5). In addition, because of precipitation problems, special precautions must be made not to mix P fertilizers with calcium nitrate and iron. To avoid precipitation problems, two stock tanks should be used, one for calcium nitrate and iron chelate, and the other for the remaining fertilizers. Applying and incorporating all the P before planting, based on a soil test, is another way of avoiding precipitation problems. Basic Mixing Rules Mixing fertilizer containing calcium with a fertilizer containing sulfate can cause gypsum to precipitate. One example of this would be mixing calcium nitrate with potassium sulfate. While both of these fertilizers are water-soluble, mixing them together into irrigation water will cause calcium sulfate or gypsum to form, which is much less soluble and which will precipitate out of the water.
Before a drip system is used to inject fertilizer, the irrigation water should tested for any potential to form precipitates through water-fertilizer interaction. As a first step, the water should be analyzed for calcium, magnesium, bicarbonate, and sulfate content. Concentration of any of these elements exceeding 2.5 meq/liter suggest a potential to form precipitates when mixed with certain fertilizers. Next step, the fertilizer should be mixed into a container of irrigation water at the concentrations desired for fertigation. The mixture should then be covered and held for the length of time approximating the period the fertilizer would be present in the irrigation system. If the water turns cloudy or white,
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Technical manual for “Fertigation manual: Open-field crops and date palm"
or if a precipitate collect on the bottom of the container, precipitation will probably result from injecting the fertilizer into the irrigation water. This testing procedure may have to be repeated frequently, particularly when phosphate fertilizers are used, since characteristics may differ by manufacturer. The following are some advances to be considered when preparing the stock solution:
DO NOT mix fertilizers containing phosphorous with fertilizer containing calcium without performing the “Jar Test” Hard water, combined with phosphate or sulfate compounds will form insoluble substances. Always fill the mixing container with 50-75% of the required water to be used in the mixture Always add the liquid fertilizer to the water before adding dry soluble fertilizer. Always add the dry ingredients slowly with mixing or agitation Always put acid into water, not water into acid DO not mix a compound containing sulfate with another compound containing calcium. The result will be a mixture of insoluble gypsum
Table 7. Can be used as a guideline for determining if mixing fertilizers with water or other chemicals may create a potential clogging problem.
Table 7. Product compatibility chart for mixing differen fertilizers.
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Technical manual for “Fertigation manual: Open-field crops and date palm"
Precipitation Precipitation is the most important limiting factor of the fertigation system. Precipitation occurs because of:
I. Reactions in a non-suitable mixture of fertilizers.
II. Reaction between the dissolved fertilizers to the salts that exist natural in the irrigation water. Soil- nutrient safety margins In calculating the nutrient supply capacity of a soil, the whole amount of the available nutrient to full depletion of soil can be taken into consideration. However, it is preferable that a certain amount of nutrient be reserved in soil. For intensive irrigated agriculture as safety amounts of P and K in soil could be considered the 30 and 100 ppm, respectively. The farmers in intensive irrigated agriculture are not encouraged to deplete soil below these values. These margins are at the same time the pool for increased demand in nutrients at eventual crop critical nutrient stages. Nutrient sources (fertilizers) The choice of fertilizer suitable for a specific application should base on several factors: nutrient form, purity, solubility, and cost.
Solubility is an issue with potassium products. Potassium chloride is expensive and reasonably good if salinity is not a problem. Potassium nitrate is the preferable form.
Liquid P fertilizers, except for food-grade phosphoric acid, may have impurities that complicate the already difficult task of eliminating chemical precipitation in the drip lines. With sufficient knowledge and attention to detail, fertilizer-grade phosphoric acid and ammonium phosphate solutions can be delivered successfully. Salt Index The Salt index of fertilizer is a measure of its contribution to the salinity of the soil solution. The lower the salt index, the less the contribution (Table 8)
In Table 8. The salt index of potassium chloride is 114, but that of potassium sulfate is only 46 at the same concentration. The higher the salt index of the solution, the lower the resistance, and the higher the electrical conductivity of the solution. When the resistance is too low, meaning when the salt index is too high, the plants need energy to overcome the osmotic pressure in order to absorb water and nutrients. When the resistance is too low, the mass of nutrients available for absorption might be too low if not supplemented in time.
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Technical manual for “Fertigation manual: Open-field crops and date palm"
Table 8. Salt index for different fertilizers
Salt Index (Sodium Compound Nitrate=100) Nitrogen Ammonium nitrate, 34% N 105 Ammonium sulfate, 21.2% N 69 Calcium nitrate1, comm. grade, 15.5% N 65 Sodium nitrate, 16.5% N 100 Urea, 46.6% N 75 Nitrate of Soda Potash, 15% N, 14% K20 92 Natural organic, 5% N 4 Phosphate Normal Superphosphate, 20% P2O5 8 Concentrated Superphosphate, 45% P2O5 10 Concentrated Superphosphate, 48% P2O5 10 Monoammonium phosphate, 12% N, 62% P2O5 30 Diammonium phosphate, 18% N, 46% P2O5 34 Potash Potassium chloride, 60% K2O 116 2 Potassium nitrate 13% N, 46% K2O 74 Potassium sulfate, 46% K2O 46 Monopotassium Phosphate, 52% P2O5, 34% K2O 8 Sulfate of potash-magnesia, 22% K2O 43 Potassium chloride KCl 116 (Boman and Stover, 2002)
1May cause clogging if irrigation water is high in bicarbonates.
2 Not recommended for use with calcium nitrate or if irrigation water is high in calcium. Fertilizers Properties for Fertigation The irrigation water should characterized by the following:
High solubility at field temperature. Complete solubility of Fertilizers. Not creating low solubility compounds with ions dissolved in irrigation water. No drastic changes of water pH (3.5 < pH < 9). Low corrosion to protect metal parts in the control head and system. No noticeable fertilizer traces in water system. No foliar injury.
Applying the right amounts of fertilizer Drip irrigation makes it possible to match the amount of nitrogen fertilizers to the needs of the crop at each growth stage to improve crop yield, reduce fertilizer costs, and cut down on nitrate leaching. Applying the right amount of fertilizer requires knowing:
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Technical manual for “Fertigation manual: Open-field crops and date palm"
The fertilizer requirements of the crop at each growth stage Fertilizer concentrations in the irrigation water The fertilizer level in the soil and organic matter
6. Setting fertigation system The fertigation unite usually installed before the filtration system in order to reduce the clogging problem in the irrigation system(Figure 2.)
Fertigator
Disc filter
Figure 2. Fertigation unit and disc filtration system
Selecting an Injector There are different types of fertilizer injectors are using in fertigation system ranged from traditional simple fertigation to automatic one. The selection of injectors depends on the farm situation, farmer education level, availability of electricity and the cost. The following is some comment fertigators are used injectors in UAE. Venturi Bypass Water flowing through the venture creates a suction that draws the fertilizer solution into the line. The “hozon” is the simplest type of venture injector (Figure 3). Other venturi units up to 25 mm in diameter are available. This injection method is inaccurate because pressure and flow rates vary in a drip irrigation system.
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Technical manual for “Fertigation manual: Open-field crops and date palm"
Figure 3. Venture Injector
Metering Pumps These inject fertilizer directly into the line at a uniform rate. Small electric pumps can be used (Figure 4). Diaphragm pumps are more reliable than piston pumps, because the corrosive fertilizer solution does not contact any moving metal parts. Water-driven piston or diaphragm pumps, recent developments, draw a known volume of solution and force it into the irrigation line.
Figure 4. Automatic fertigator
Hydraulic Units The “Dosatron,” a water-driven proportional injection unit, was originally designed for industrial uses and injecting chlorine into city water supplies. Fertilizer from a tank is drawn into the injector pump as drive water pushes the pump piston upward. Once the piston reaches its highest point, a valve in the unit creates a pressure difference and reverses the flow of water, causing the piston to begin its downward movement. As the piston moves
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Technical manual for “Fertigation manual: Open-field crops and date palm"
downward, the water that originally pushed the piston upward is injected with a dose of fertilizer and released into the main line of irrigation water. (Figure 5)
Figure 5. Hydraulic injectors
Conventional flow by-pass tank We recommend to us the hydraulic injectors because of its higher fertilizer application efficiency and no requirements for electricity. While using conventional flow bypass tank fertigators ( Figure 6) are not recommend due to its low distribution efficiency specially under sandy soil conditions. The main limitation of this fertegator is that the nutrient concentration is variable during irrigation (high concentration in the beginning of irrigation and very low concentration at the end of irrigation event)
Figure 6. Conventional Flow bypass fertigator
7. Fertigation under saline conditions Under saline conditions, specially where the water EC>1.0 dS/m, which is common in arid zones, care should be taken to minimize the amount of accompanying ions added with N or K. For example, KCl should be replaced by KNO3 and K2HPO4, while NH4NO3 and urea should be preferred over (NH4)2SO4. Sodium-based fertilizers (e.g. NaNO3 or NaH2PO4)
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Technical manual for “Fertigation manual: Open-field crops and date palm"
Are unlikely sources due to the adverse effect of Na on soil hydraulic conductivity and on plant functioning. With balanced fertigation good results can be obtained under saline conditions. Elevated salt levels Certain geographic areas have high salt levels in the water. High boron, fluoride, chloride, sulfates and sodium:
Can cause poor plant growth. May influence soluble salt levels in the water. High iron, especially in “hard water” (having high Ca and Mg): Can cause rusty spots on leaves with overhead irrigation. High salt levels can also cause rapid salt buildup on cooling pads in the greenhouses. May need to bleed off and replace pad water regularly
Nutrient interactions Plants maintain a balance between the cations (positively charged ions) and anions (negatively charged ions) in their cells and tissues. Plants also maintain a constant sum of cations in their cells and tissues. Therefore, if one cation is increased, it may decrease the uptake of others.
Ex: Increasing Mg++ can cause decreases in Ca++ and calcium deficiencies.
+ ++ Ex: Increasing NH4 (to increase acidity) can cause decreases in Ca uptake.
Interactions between anions are not as common.
- - Ex: Increasing Cl can decrease NO 3 uptake and visa versa. Nutrient uptake rates and mobility Plant roots take up mineral nutrients at different rates.
-3, - +2 -2 Ex: NO K+ and Cl are taken up quickly; Ca and SO4 are taken up slowly. This results in unequal removal of nutrients from the solution. Once in the plant different ions have different mobilities within the plant.
-2 Ex: Mobile ions include N, K, P (PO4 ), Mg and Cl.
Deficiency symptoms for these ions usually appear in the old growth. Slightly mobile ions -2 include S (SO4 ), Mn and Mo. Deficiency symptoms usually appear in the middle and old growth. Immobile ions include Ca, B, Zn, Fe and Cu. Deficiency symptoms for these ions usually appear in the new growth.
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Technical manual for “Fertigation manual: Open-field crops and date palm"
8. Fertilizers application The fertilizer solution in liquid form is fed into the system at low rates repeatedly, on a continuous basis, during irrigation. The flow rate of the injector should be such that the calculated amount of solution is supplied at a constant rate during the irrigation cycle, i.e. starting fertigation right after the system starts operation and finishing a few minutes before the operation ends. Regarding the choice of the fertilizers, apart from the amount and the kind, other parameters need to be considered, such as solubility, acidity, compatibility and cost. Solubility The fertilizer stock solution should always be dissolved in a separate container (Figure 7) and then poured into the suction tank. The types of fertilizer should be highly soluble and when dissolved in water must not form scums or sediments which might cause emitter clogging problems. The solution should always be agitated, well stirred and any sludge deposited in the bottom of the tank should be periodically removed. The injector suction pipe should not rest on the bottom of the tank. Hot water helps dissolve dry fertilizers. Their degree of solubility varies according to the type and the country of origin. Potassium sulfate seems to have a low solubility of approximately 1:8, i.e. 1 kg of dry fertilizer in 8 liters of water. The solubility of Ammonium sulfate (21-0-0) is 1:1.3, while urea nitrate (46-0-0) has a high solubility of approximately 1.2:1 at room temperature 25 Co (Table 9).
Figure 7. Weighing the fertilizer and preparing the stock solution
Example 3 – Fertigation of vegetables • Crop: Tomatoes;
The nutrient requirements to produce 80 ton/ha from Table 5 N(kg/ha) = 80 (ton/ha)*3.0(kg/ton) =240 kg/ha
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Technical manual for “Fertigation manual: Open-field crops and date palm"
P(kg/ha) = 80 (ton/ha) *0.6(kg/ton) = 48 kg/ha K(kg/ha) = 80 (ton/ha) *3.5(kg/ton) = 280 kg/ha If the seasonal water applied is 6000 m3/ha
Then crop requirement of NPK fertilizers in gm/m3 (kg/ha*1000gm/kg/(6000m3/ha)): 240 (kg/ha)*1000(gm/kg)/ 6000(m3/ha) = 40gm/m3 N 48 (kg/ha)*1000(gm/kg)/ 6000(m3/ha) = 8 gm/m3 P 280 (kg/ha)*1000(gm/kg)/ 6000(m3/ha) = 70 gm/m3 K
Type of fertilizers available:
Ammonium sulfate (21.2- 0-0);
Monoammonium phosphate MAP (12-62- 0); Potassium Sulfate (0-0-46)
System flow:40 m3/h;
Irrigation dosage: 20 m3;
Duration of application: 0.5 hours.
Phosphate and potassium are given in oxides, therefore they are converted into P and K elements by multiplying by 0.4364 and 0.8302 respectively. Solution Calculation of the amounts of fertilizers needed in kg per cubic meter of water: From Table 6. N, P, and K uptake efficiency by drip irrigation for sandy soil (0.75, 0.25 and 0.80, respectively)
3 3 K =40/0.75 x 100 ÷ (46 x 0.8302) =140gm /m = 0,140 kg K2O/m
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Technical manual for “Fertigation manual: Open-field crops and date palm"
3 P = 8 /0.25 x 100 ÷ (62 x 0.4364) = 118.3 gm/m = 0.118 kg /m3 (NH4)2HPO4 This amount also provides 21 gm of N.
3 N = (47-21)/0.80 x 100 ÷ 21.2 =154 gm/m = 0.154kg/m3 NH4NO3 Thus, for 20 m3 of water, which is the irrigation dosage, the exact quantities are:
0,140 kg /m3x 20 m3 = 2.8 kg Potassium Sulfate
3 0.118 kg/m3 x 20 m = 2.36 kg NH4 HPO4 0.154 kg/m3 x20 m3 = 0.308 kg Ammonium sulfate The amount of water needed for the dilution of the above quantity of fertilizers is estimated by taking into account the solubility of the fertilizers 25 Co from Table 9. 2.8 kg Potassium Sulfate x (1000/120) liters = 23.3 liters 2.36 kg MAP x (1000/410) liters = 5.76 liters 3.08 kg Ammonium sulfate x (1000/770) = 4 liters Minimum amount of water needed 33.06 liters to dissolve the required fertilizers If the fertilizers are diluted in 40 liters of water and the duration of the irrigation is 0.5 h ( 30 min), then the injection rate should be about 65 l/h
Table 9. The Influence of Temperature on the Solubility of Fertilizers (gr./liter) in Distilled Water
Fertilizers Temperature C0 0 5 10 20 25 30 Ammonium sulfate 700 715 730 750 770 780 Urea 680 780 850 1060 1200 1330 Potassium chloride 280 300 310 340 365 370 Potassium sulfate 70 80 90 110 120 130 Potassium nitrate 130 170 210 320 370 460 Mono ammonium phosphate 227 255 295 374 410 464 (Wolf et al., 1985)
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Technical manual for “Fertigation manual: Open-field crops and date palm"
Acidity The acidity produced by the several forms of nitrogen varies from type to type and is greatly affected by the kind of irrigation water and the type of soil. At least one check on the soil pH should be carried out at the beginning of the season and one at the end. Furthermore, a complete ionic analysis of the water is necessary. Quantity a simple method for calculating the amount of fertilizer required for fertigation is to divide the annual application by the number of irrigations. Various recipes have been developed in different countries based on the conventional nutrition dosages. The total quantity of fertilizers applied is also related to the length of the growing season and the irrigation requirements.
Initial chemical water measurements are necessary to determine its suitability for use in fertigation. The pH of the water has to be near to neutral and its EC to be within acceptable limits that are not well defined, but a value of around 1 dS/m is acceptable. Addition of fertilizers to the water raises its EC and changes its pH. The objective is to have a fertigation solution somewhat acid and with low EC. These parameters are decisive for choosing a fertilizer combination compatible with the water quality. For water with a relatively high EC, the ratio of cations Na to Ca Mg is important to prevent potential alkalization of the soil. The level of bicarbonate is important for the selection of the P fertilizer. In water with relatively high bicarbonate level, mostly coupled with Ca, precipitation of orthophosphate compounds is very likely. In such cases, the use of polyphosphate fertilizers would be preferred. Monitoring the fertigation water quality is a major tool for controlling plant nutrition in soilless culture. The number of irrigation cycles per day is varied according to the crop and the season. Frequency of irrigation should be regulated so that 20-30% of the applied water appears in drainage. The pH of the fertigation solution leaving the dripper and that collected in drainage should be monitored frequently. The optimum pH of the fertigation water is 5.5-6.0 (Figure 8). A pH lower than 5.5 indicates a need to revise the composition of the fertigation solution. The anticipated EC of the fertigation solution is calculated by measuring the EC of irrigation water prior to addition of the fertilizer solution and adding to it the estimated EC of the fertilizer solution. The measured EC of the fertigation solution collected from the dripper should be within 10% of the calculated value. Any deviation greater than this, necessitates checking the fertilizer injection devices, the fertilizer dilution process or composition of the
Fertilizer solution. Comparing the EC in the fertigation solution to that in the drainage water indicates the risk of salinization of the growth medium. A similar EC in both solutions is normal and if the EC of the drainage solution is more than 20% higher than that of the fertigation solution there is a risk of salinization. Excess of chlorides in the drainage water indicates that the higher EC is caused by irrigation water salinity. In this case, the amount of water applied has to be increased to enhance salt leaching from the growth medium. Comparing nutrient concentrations in the fertigation solution and drainage water indicates the extent of nutrient uptake. Excessive amounts of nutrients in the drainage water show that the rate of nutrient application should be reduced. An EC value in the drainage water
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Technical manual for “Fertigation manual: Open-field crops and date palm"
that is lower than that in the fertigation solution indicates a high uptake of nutrients and an increase in the nutrient application rate should be considered. Measuring the nitrite concentration in the drainage water monitors the level of aeration in the growth medium, the presence of nitrites indicates anaerobic conditions. In normal well-aerated media, N compounds are fully oxidized to N03 and no nitrites are found. Increasing the interval between irrigation would, in most cases, relieve the anaerobic condition. Controlling the fertigation system requires frequent analyses of both the fertigation and the drainage solution on pH, EC, nitrate, ammonium, chloride, calcium, magnesium, phosphate, potassium, sodium, bicarbonate and micronutrients. Imbalance nutrient application will cause the deficiency to the others like Ca in cucumber (Figure 9) and Mn and Fe (Figure 10) in Tomato crop.
Figure 8. Nutrient availability under different soil pH (Barber, 1984)
Figure 9. Ca deficiency septum's in Cucumber crop
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Technical manual for “Fertigation manual: Open-field crops and date palm"
Figure 10. Mn and Fe deficiency in Tomato crop
9. Soil Testing The soils are generally used as the growing medium in most high tunnel systems and therefore the first step in managing fertility in a high tunnel is to obtain a routine soil test. Soil pH, P, K, Ca, Mg, and micronutrients should be monitored every two to three years or more often if problems are occurring. In addition, a soluble salts test (also known as an electrical conductivity test) is recommended each year to ensure that salts are not building up. Most soils in the arid region have low soluble salts, but with the use of fertigation and the absence of leaching rainfall, salts may accumulate in a high tunnel. If salt levels become excessive, leaching of the growing beds or removal of the soil may be necessary. A nitrate- nitrogen soil test should also be done on an annual basis. Nitrate-N is a plant available form of N that can carry over in the soil from the end of one growing season to the beginning of the next. Collect soil samples for nitrate-N from the upper 30 cm the of soil (Figure 11), rather than the standard 15 cm sampling depth for other soil tests. The amount of nitrate- N in the soil before planting can be subtracted from the N fertilizer requirement for the crop.
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Technical manual for “Fertigation manual: Open-field crops and date palm"
Figure 11. Soil sampling
Organic Matter The ideal soil for high tunnel production is a well-drained sandy loam to silt loam. Soil organic matter should be medium to high, in the range of 3.5% to 6%. Compacted soils should be plowed to relieve the compaction. Considerable soil compaction can occur during the construction process, so tillage is necessary after the structure is completed. Manure- based compost has a higher nutrient content than crops waste compost and can be applied at the lower rates. The compost should be incorporated in the soil to a depth of 15 to 20 cm before planting. Determining nutrient requirements Before installing the drip irrigation system, have a soil sample tested to determine its nutrient content. This should include nitrogen, phosphorus, potassium and minor nutrients. The nutrient requirements of your plants change throughout the season, and your fertigation program should reflect this. If possible, obtain data on the nutrient requirements of your crop at each growth stage. In combination with tissue testing throughout the season. This information will allow you to maximize the efficiency of your fertigation program. Soil chemical analysis as a tool for evaluating nutrient availability. Have the soil tested 1–2 months prior to planting so that liming requirements might be addressed well in advance of planting. A soil test will also assess levels of available
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Technical manual for “Fertigation manual: Open-field crops and date palm"
phosphorus, potassium, magnesium, sulfur, calcium, and micronutrients (minor elements) in the Soil testing and plant tissue analysis provides the basis for fertilizer applications aimed at profitable and quality crop yields. Proper collection of samples and correct interpretation of analytical results is vital for correct assessment of crop fertilization needs. This chapter provides farmers and fertilizer users with background information on proper methods for collecting representative soil and plant tissue samples and for interpreting the results of analysis in order to estimate crop fertilizer requirements. Soil sampling and analysis Soil analysis is recommended before establishing agricultural activities. For most soils in arid and semi-arid regions, a soil test of physical and chemical properties should be conducted before making a decision regarding the suitability of the land for agricultural development. In addition, soil sampling should be carried out every three years in order to develop suitable fertilization programmes.
Good management of soil phosphate, potash and magnesium depends on regular soil sampling and analysis. Levels of these nutrients in the soil change only slowly so soil sampling and analysis can be done every 3-5 years at an appropriate time in the crop rotation. It is usually safe to use soil analysis results for phosphorus, potassium and magnesium as a basis for fertilizer recommendations for up to 4 years from the date of sampling. The analytical results will be meaningful only if an adequate and representative soil sample is taken. Depth of soil sampling Samples are usually collected from the soil surface to the plough depth of 15 cm in cultivated fields. Where farmers plough to a depth of 30 cm, the samples should be collected to a depth of 30 cm. With field crops and vegetables, it is advisable to collect soil samples from the soil surface 0–15 cm and subsurface 15–30 cm. Soil analysis is appropriate before an orchard is planted; the depth of soil sampling should be extended to the depth of the root zone, 0–30, 30–60 and 60–100 cm where the root system reaches about 100 cm of depth. However, in established orchards, leaf analysis is the most reliable indicator of nutrient levels in fruit trees. Method of soil sampling Representative soil samples should be collected properly from the field. A good soil test, no matter how accurate, cannot compensate for a poor sample. It is the sample taker’s responsibility to take a truly representative composite soil sample from the field. In order to be able to use the results of soil testing as a reliable guide for the addition of fertilizers, the collected soil samples must represent the soil condition of the area sampled, and the specific purpose of the test must be kept in mind. Truly representative and unbiased samples can be taken by considering the following:
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Technical manual for “Fertigation manual: Open-field crops and date palm"
Avoid areas or conditions that are different, such as areas where fertilizer or other materials have been spilled, gate areas, poorly drained areas, dead furrows, tillage or fertilizer corners or fertilizer band areas of the previous year’s crops. It is also advisable to stay at least 25 m away from barns, roads, lanes, irrigation canals and fences.
Because of soil variations, it is necessary that each sample consist of small portions of soil obtained from about 15 locations (minimum 7) in the soil area. After obtaining these portions of soil, mix them together to make a representative sample. Air-dry the samples and place about 500 g of soil in a clean plastic bag. This method of sampling After the sample has been taken, the soil sample bag should be marked clearly with the name of the collector, address, sample number and identification of the field; this information should be kept in a record book.
Where recommendations are desired, fill out the soil information sheet as completely as possible (this helps in making recommendations). The sample numbers on the soil information sheet should correspond to the numbers on the sample bags.
After the samples have been taken, they must be handled as follows:
Label the sample Mark the sample list to indicate that the sample has been collected. Seal the sample containers properly. Keep samples in the shade until they can be transported to the office. Laboratories may have special requirements or procedures for sample handling and storage.
Interaction of soil analysis results From the results of soil analysis, farmers can predict fertilizer requirements. Soil analysis measures the amount of elements extracted by certain chemical solutions that are correlated to the quantity of nutrients available for plant uptake in a certain soil (Table 10). Therefore, fertilizers are applied only where a crop is expected to respond to fertilization. Soil analysis should be performed by an experienced analyst in a well-equipped laboratory. Portable field kits are of limited benefit to farmers and should be always checked through field calibration.
The prevailing soil properties under arid climate are generally characterized by neutral to slightly high pH and CaCO3 content, as well as low organic matter (OM) content, which together cause the reduction in N, P and micronutrient availability that is accentuated further in some soils by the occurrence of high salinity. Therefore, in most arid area, micronutrients are insufficient for meeting the crop genetic potential, especially for high- yielding varieties
Table 10.Recommended soil analysis and expected nutrient concentrations (ppm) in soils of arid regions
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Technical manual for “Fertigation manual: Open-field crops and date palm"
Element Very low Low Medium High Very high Residual nitrate N 0-10 10-20 20-40 40-60 > 60 Calcium1 0–500 500–1200 1200-2500 2500-3500 >3500 Phosphorous 0–7 7–15 15–30 30–50 > 50 Potassium 0–85 85–170 170–300 300–500 > 500 Magnesium 0–85 85–200 200–300 300–500 > 500 Sodium – – 0–300 > 300 – Iron 0–2 2–4 4–6 6–10 > 10 Manganese 0–0.5 0.5–2 2–5 5–10 > 10 Zinc 0–0.5 0.5–1.5 1.5–4 4–6 > 6 Copper 0–0.1 0.1–0.3 0.3–0.8 0.8–3 > 3 Boron 0–0.5 0.5–1 1–2 2–4 > 4 Molybdenum – 0–0.1 0.1–2 2–5 5–102 Sulphur 0–10 10–20 20–35 35–50 > 50 Calcium – 0–5 5–15 15–25 > 25 1 In calcareous soils, exchangeable Ca values could be 50–100 percent higher than the above values.
2 Molybdenum levels > 10 ppm are toxic to plants.
Soil salinity (EC of soil saturated extract, in dS/m): 0–4 no hazard; 4–6 low hazard; 6–8 medium hazard; 8–10 high hazard;
> 10 very high hazard. 10. Date palm fertigation and Fertilization applications In California fertilizer is applied according to the size and age of the tree in a ratio of 2 N :
1P2O5 : 3 K2O Following are the quantities of nitrogen applied according to the above ratio:
Young trees, up to 18 months: 0.3 kg N/tree/annum
Small trees: 0.5 – 1.0 kg N/tree/annum
Medium size trees: 1.5 – 2.0 kg N/tree/annum
Large trees: 2.5 – 3.5 kg N/tree/annum
It is necessary to test for microelement deficiencies and spray the foliage when necessary with S, Cu, Fe, Mg, Mn. If the trees are medium size the fertilizers requirement according
California recommendations for each tree 2kg N : 1P2O5 : 3K2O for one hectare we need
200kg N : 100 P2O5 : 300 K2O. In Iraq it is customary to apply 20 kg of organic fertilizer per tree per annum.
Table 11. shows a practical example on Date palm crop water requirement under UAE condition for mature tree irrigated with water salinity of 4200 ppm. To reduce the salinity
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Technical manual for “Fertigation manual: Open-field crops and date palm"
effect high frequent irrigation interval are used (three irrigations per day) using inline PC dripper irrigation system, for each tree 35 inline GR drippers fixed around each tree in 0.4 m distance between the drippers with 8 lph discharge. Table 11. Date palm crop irrigation application rate and time of each irrigation per tree calculated for mature trees under UAE conditions.
Applied water amount ( L / tree per Time of each irrigation Month irrigation event) event ( mint) Jan 28,3 6,1 Feb 31,7 6,8 Mar 48,3 10,4 Apr 73,3 15,7 May 100,0 21,4 Jun 98,3 21,1 Jul 98,3 21,1 Aug 78,3 16,8 Sep 83,3 17,9 Oct 56,7 12,1 Nov 41,7 8,9 Dec 30,0 6,4 *irrigation water salinity is 4200 ppm,35 GR PC emitters in 0.4 m distance installed around each tree with the emitters discharge of 8 Lph. Application of three irrigation per day. Fertigation Calculations In fertigation system the farmer should apply fertilizer continuously with irrigation by calculation of the amount of fertilizer required to prepare the concentrated stock solution.
Example 4. A field grown with Date palm trees of the following nutrient requirements; 100 N : 50 P : 150 K. Prepare stock solution in reservoir 1 m3 volume from the following available fertilizers:
Calcium Nitrate (15.5 N : 0 P2O5: 0 K2O) mono-potassium phosphate (MKP) (0 N : 52 P2O5: 34 K2O)
Potassium Sulfate (0 N : 0 P2O5 : 46 K2O) Characteristics of the irrigation and fertigation systems With direct measurements in the field it has been found that : Flow rate of the irrigation system is 15000L/hr
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Technical manual for “Fertigation manual: Open-field crops and date palm"
Flow rate of the fertigator is 100 L/hr The capacity of the reservoir for the stock solution is 1 m3
Calculate the fertilizers weights to be dissolved in 1 m3
Using the following equation
퐅∗퐃퐅∗퐧∗ퟏퟎퟎ 푪 = Where; 풂 C= Weight of the fertilizer (gm) in the stock solution F= Desired concentration of a nutrient in the irrigation water (gm/m3) n = Volume of the reservoir for the stock solution (m3) a = % of a pure nutrient in the fertilizer DF = Dilution Factor 퐅퐥퐨퐰 퐫퐚퐭퐞 퐨퐟 퐭퐡퐞 퐢퐫퐫퐢퐠퐚퐭퐢퐨퐧 퐬퐲퐬퐭퐞퐦 푫푭 = 푭풍풐풘 풓풂풕풆 풐풇 풕풉풆 풇풆풓풕풊품풂풕풐풓 Solution
ퟏퟓퟎퟎퟎ 푫푭 = = 150 ퟏퟎퟎ Calculations for N
퐠퐦 ퟏퟎퟎ ( ) ∗ ퟏퟓퟎ ∗ ퟏ 퐦ퟑ ∗ ퟏퟎퟎ 푪 = 퐦ퟑ ퟏퟓ. ퟓ = 96.77 kg of Calcium Nitrate will dissolved in 1 m3
Calculations for P Since we selected MKP and Potassium Sulfate contain K in both of them so first we will calculate P from MKP
퐠퐦 ퟓퟎ ( ) ∗ ퟏퟓퟎ ∗ ퟏ퐦ퟑ ∗ ퟏퟎퟎ 푪 = 퐦ퟑ ퟓퟐ/ퟐ. ퟐퟗ = 33.03 kg of MKP will dissolved in 1 m3 But the 33.03 kg of MKP contains (33030 *34*1/1.2/(150*1*100 )= 62.4 (gm/m3) K The required K is 150 -62.4= 87.60 (gm/m3) Calculations for K
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Technical manual for “Fertigation manual: Open-field crops and date palm"
퐐퐮퐚퐧퐭퐢퐭퐲 퐨퐟 퐏퐨퐭퐚퐬퐬퐢퐮퐦 퐒퐮퐥퐟퐚퐭퐞 퐟퐞퐫퐭퐢퐥퐢퐳퐞퐫
퐠퐦 ퟖퟕ. ퟔ ( ) ∗ ퟏퟓퟎ ∗ ퟏ 퐦ퟑ ∗ ퟏퟎퟎ 푪 = 퐦ퟑ ퟒퟔ/ퟏ. ퟐ =34.28 kg 퐨퐟 퐏퐨퐭퐚퐬퐬퐢퐮퐦 퐒퐮퐥퐟퐚퐭퐞 will be dissolved in 1 m3 . stock solution tank Summary of the fertilizers needed In a reservoir of 1m3 the following amounts of fertilizers are needed to provide 100, 50 and 150 g/m3 of N, P, K, respectively, the farmer should refill the fertilizer reservoir continuously with the same nutrient concentration when it getting empty from the following fertilizers:
Calcium Nitrate = 96.77 kg MKP = 62.4 kg Potassium Sulfate = 34.28 kg
Table 12. shows the possible cause of macro and micro nutrient elements deficiency and the possible solution to take action.
Table 12. Troubleshooting in fertigation a form of problem solving to repair failed products
Nutrient Possible Cause Possible Remedy Element
N Too much fertilizers Split the mass / volume of fertilizers applied applied at a time at any one time
Excess leaching Reduce the application of water to wet the root-zone only
Phytophtora infection of Test the roots for Phytophtora and act the roots accordingly
Low efficiency of applied Foliar sprays with low biuret urea or fertilizers potassium nitrate
P Too high soil pH Apply single or double super phosphate in a narrow strip on the soil
Too low soil pH Apply lime to increase the pH to 6.50
Foliar sprays with phosphates are not effective.
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Technical manual for “Fertigation manual: Open-field crops and date palm"
K Too high concentration of Use potassium nitrate to apply some of the magnesium in the soil or nitrogen required water
Salinity Locate the source and act accordingly
Low efficiency of applied Foliar sprays with low potassium nitrate fertilizers
Poor root health Take remedial actions
Old trees Rejuvenate the root system
Compaction Corrective actions with mechanical implements may be used, but are not always successful
Nematodes Test the roots for nematodes and act accordingly
Ca Climatic conditions Ensure that enough available calcium is present in the root zone during the critical period from budding to petal drop
Low pH Apply lime
Salinity Locate the source and act accordingly
Low calcium saturation Apply lime, gypsum or calcium nitrate
Foliar sprays with calcium have limited Success
Mg Too high concentration of Apply magnesium nitrate foliar sprays potassium in the Soil
Low pH Apply dolomitic lime
Foliar sprays with Apply magnesium nitrate foliar sprays potassium nitrate
S Too low concentration of S Apply sulphates to the soil. The efficacy of in the soil foliar sprays is unknown.
Nutrient Possible Cause Possible Remedy Element
Cu Too low concentration of Apply foliar sprays. The efficacy of soil Cu in the soil application depends on many soil factors.
Fe Too high pH in the soil Apply Fe-EDDHA in August
Water logging Improve scheduling and drainage
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Technical manual for “Fertigation manual: Open-field crops and date palm"
Zn Too high pH in the soil Apply foliar sprays
Recent liming Apply foliar sprays
Soil applications to mature trees are not effective
B Too low pH in the soil Apply foliar sprays
Recent liming Apply foliar sprays Apply foliar sprays
Mn Foliar sprays with iron are not effective
Too high pH in the soil Apply foliar sprays
Recent liming Apply foliar sprays
Zn Too high pH in the soil Apply foliar sprays
High P status Apply foliar sprays
Soil applications to mature trees are not effective
B Too low pH in the soil Apply foliar sprays
Recent liming The applications of boron to the soil is quite effective under most soil conditions
Mo Too low soil pH Apply lime. Apply foliar sprays.
The status of various nutrients in the tree has a marked effect on fruit quality. Nitrogen, phosphorous, potassium and calcium play the most important role.
To correct the nutrient status of the tree, the cause of the over- or undersupply must be known. Applying more fertilizer may not be an effective remedy.
11. References Ayers, R.S. and W. Wescot. 1989.Water quality for agriculture, FAO Irrigation and Drainage paper 29 Rev. 1.
Barber, SA. 1984. Soil nutrient availability: Mechanistic approach. John Wielly and Stone. NY.
Boman, B.J. and E. W. Stover, 2002.Managing salinity in Florida citrus. University of Florida, Institute of Food and Agricultural Sciences (UF/IFAS)
Doorenbos, J. and W.O Pruitt. 1975. Guidelines for predicting crop water requirements, Irrigation and Drainage Paper 24, Food and Agriculture Organization of the United Nations, Rome, 179 p.
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Technical manual for “Fertigation manual: Open-field crops and date palm"
IFA (1992) World fertilizer use manual. International Fertilizer Industry Association, Paris, France.
Maas, E. V. 1984. Salt tolerance of plants. The Handbook of Plant Science in Agriculture. B. R. Christie (ed). CRC PRESS, Boca Raton, Florida
Maas, E.V. and G.J Hoffman. 1977. Crop salt tolerance - current assessment. J. Irrig. and Drainage Div., ASCE 103 (IR2): 115-134.
Papadopoulos, I., L. Ristimaki, and C. Sonneveld. 2000. Nitrogen and phosphorous fertigation of tomato and eggplant. Acta Horticulturae. 511: 73-79.
Wolf, B., J. Fleming and J. Batchelor. 1985. Fluid Fertilizer manual. Vol. 1. National Fertilizer Solutions Association, Peoria I1.
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