Advantages Relatively uniform fertilizer applications Flexibility in timing of applications Less fertilizers used Reduced costs
Disadvantages z
z z
Potential contamination hazard from equipment malfunctions Backflow prevention devices required Careful handling of liquid fertilizers required
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Maximize profit by applying the right amount of water and fertilizer Minimize adverse environmental effects by reducing leaching of fertilizers and other chemicals below the root zone
1
Maximizing Profit - Applying the Right Amount of Nitrogen ¾ ¾ ¾
Nitrogen requirements of the crop at each growth stage Nitrate concentrations in the irrigation water and the soil Amount of nitrogen in the fertilizer
What Contributes to Fertilizer Leaching Under MicroMicro-Irrigation? ¾ ¾ ¾ ¾
Adjusting for Nitrogen in Irrigation Water
Excessive fertilizer application Excessive water application Poor field wide uniformity of water and fertilizer applications Localized nonuniformity
Calculating the Injection Rate PN x A x 100 IR = PG x %C x IT
1 ppm N = 0.23 pounds of N per acre-inch of irrigation water
1 ppm NO3 = 0.051 pounds of N per acre-inch of irrigation water
IR = Injection rate (gallons per hour) PN = Pounds of nutrient per acre A = Acres PG = Pounds per gallon of fertilizer %C = Percent concentration of nutrient IT = Injection time (hours)
2
What Affects the Uniformity of Fertilizer Applications under MicroMicro-Irrigation? ¾
Field wide variability z Varying injection rate z Varying emitter discharge rates
Maximum uniformity of fertilizer equals the uniformity of applied water Injection time must be sufficient for fertilizer to reach the furthermost part of the irrigation system Flushing time must be sufficient for fresh water to reach the furthermost part of the irrigation system Constant injection rate
40
600 ft
35
1300 ft Field A
30 25 20 15
Field B
10 5
600 ft
0 0
100
200
300
400
500
600
700
800
900
1000 1100 1200
Distance Along Lateral (feet)
3
300
50 Travel Times Total Time (minutes)
40 Elapsed Time (minutes)
Advance Recession
250
30
20
200
150 Fertilizer Application Time 100
50
10
Field A Field B
0 0
0 0
500
1000
1500
2000
2500
Distance (feet)
500
1000
1500
2000
2500
3000
Distance (feet)
3000
Injection time = 2 hours (starts one hour after start of irrigation)
Localized Nonuniformity under MicroMicro-irrigation Localized Nonuniformity – distribution of chemical around the drip line
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Soil water content decreases with distance and depth from the drip line Root density decreases with distance and depth from the drip line Chemical distribution may vary around the drip line, depending of chemical characteristics
Wetted Area Wetted Area Low Root Density Low Root Density
High Root Density
High Root Density
Tree Skirt Tree Skirt
6
Root Distribution Flood Irrigation
Tree Trunk Root Distribution -Citrus
Wetted Area
Low Root Density High Root Density Tree Skirt
Forms of Nitrogen
What Affects the Distribution of Fertilizer in the Soil? ¾
Nitrate z
¾
Type of fertilizer z z
¾
z
¾
z z
Soil type Emitter discharge rate Duration of irrigation
Fertigation strategy z z
Duration of fertigation Timing of injection relative to irrigation duration
z z z
¾
Negatively charged ion Moves readily through soil with water flow Preferred choice of N by most plants
Urea z
Water movement in the soil z
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Mobile – urea, nitrate Adsorbed – ammonium, potassium, phosphorus
z
Neutral molecule Highly soluble in water Moves readily in the soil with water flow Converts to ammonium and carbon dioxide
Ammonium z z z z
Positively charged ion Adsorbed to clay particles in the soil Does not move with water Converts to nitrate (rate at which depends on soil water content and temperature
7
Fertigation Strategies
Injection Practices
¾
Short injection times z z
¾
¾
z
Common recommendations z Inject during middle 50% of irrigation cycle z Inject during middle third of irrigation cycle Observed practices – short injection times at various times during the irrigation cycle
z
z z
¾
Long injection times z z z z
z z
Drip Loam
180
Depth (cm)
140
180
180
180
160
160
160
0.375
140
140
140
120
120
120
0.325
120
0.275 100
0.225
100
100
100
80
0.175
80
80
80
0.125
60
60
60
60
40
40
40
0.075 40
0.025
20
20
20
T=0d 0
0
20
40
60
0
0
20
40
60
T = 0.70 d 80
0
0
20
40
Distance From Emitter (cm)
60
200
200
200
180
180
180
160
160
160
140
140
140
120
120
120
100
100
100
80
80
80
60
60
60
40
40
40
2 h - beginning
20
T = 0.13 d 80
Nitrate Concentrations
200
0.425
0.475
160
200
Depth (cm)
200
Middle oneone-third or oneone-half of the irrigation set time Relatively low chemical concentration in irrigation water May reduce precipitation problems May provide better chemical distribution throughout the root zone Flushing of drip lines may not be needed May not be convenient for irrigators
Drip Loam T = 1.5 d
Soil Water Content
200
1 to 2 hours of injection Relatively high chemical concentration in irrigation water May aggravate chemical precipitation problems May result in poor distribution of chemical throughout the root zone Flushing highly recommended Convenient for irrigators
Do not start injection until irrigation water has reached the furthermost emitters Inject for sufficient time for the chemical to reach the furthermost emitters After injection, flush system with irrigation water until the fresh water reaches the furthermost emitters Maintain high uniformity of emitter discharge rates throughout irrigation system z
z z
¾
Other Considerations Frequency of applications z
z
¾ ¾
Little information on effect of injection frequency on crop yield No strong trend
FertilizerFertilizer-fertilizer interactions FertilizerFertilizer-irrigation water interactions
Avoid long periods of water application after injection of fertilizers or chemical
50 Red Fruit Yield (tons/acre)
¾
Minimize pressure variation (pressure(pressure-compensating emitters, pressure regulation, appropriate drip line lengths) Use same emitter sizes Prevent or correct clogging problems
Processing Tomatoes (weekly fertigation)
40
30
20
10
0 Daily
2/wk
1/wk
Irrigation Frequency
11
Reactions Reactions (continued) ¾
¾
CalciumCalcium-based fertilizers (CN(CN-9, CANCAN-17) - can cause calcium carbonate precipitation if more than 2 to 3 meq/l of bicarbonate is in the irrigation water Phosphorus fertilizers - can cause calcium and magnesium phosphate precipitation if more than 40 to 50 ppm (2 to 2.5 meq/l) of calcium and magnesium is in the irrigation water
¾
¾
Mixing a fertilizer containing calcium with a fertilizer containing sulfate can cause gypsum to precipitate Mixing fertilizers can be tricky - use jar test and UNOCAL guidelines
Injection Equipment ¾
Batch Tanks z z
¾
Venturi Devices z z
¾
Inexpensive, easy to use Chemical mixture becomes more and more diluted with time Requires pressure difference Inexpensive, easy to use
Positive Displacement Pumps z z z z
Piston, diaphram Electric, gasoline, waterwater-driven Injects at constant rate Expensive
