Improving Nutrient Management through Advanced Irrigation Management James Adkins Irrigation Scientist Carvel Research and Education Center Georgetown, DE
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Why Irrigate?? To maximize yield, evapotranspiration (ET) must be maximized Applying water in EXCESS of ET demand will NOT increase yield Goal: To apply enough water to meet the crop s ET demand and do so efficiently as possible
Soil Properties Available Water Holding capacity (AWC) Soil water reservoir Use irrigation to manage the reservoir Water intake rates Influences sprinkler selection Restrictive soil layers Limit water movement and root zone Limit soil water reservoir size
Soil Water Reservoir Saturation Water Available Capacity 100% 0% Water Available to Plants at low stress Water Available to Plants with stress Field Capacity 50% Minimum Balance Permanent Wilting Oven Dry
Soil Textures Medium and fine textured soils More readily managed substantial water holding capacity 10 cm to 15 cm in top 1 m. Coarse textured soils More difficult to manage Relatively small water holding capacity Less than 10 cm in top 1 m.
Available Water Holding Capacity Based on Soil Texture Available Water Holding Capacity Soil Texture (mm of water / mm of soil) Coarse Sand 0.02-0.06 Fine Sand 0.04-0.09 Loamy Sand 0.06-0.12 Sandy Loam 0.11-0.15 Loam and Silt Loam 0.17-0.23
Delaware Irrigated vs. Rain-fed Corn Rain-fed Yield Range: 0 200 bu./ac (0 12.7 Mg/ha) Applied N: 100 220 lbs./ac (112 246 kg/ha) Crop N Removal: 0 140 lbs./ac (0 156 kg/ha) Estimated NUE: 100 1 lbs./bu. (112 19.3 kg/mg) Irrigated Yield Range: 150 300 bu./ac (9.5 19.5 Mg/ha) Applied N: 200 280 lbs./ac (224 313 kg/ha) Crop N Removal: 105 210 lbs./ac (117 235 kg/ha) Estimated NUE: 1.3 -.85 lbs./bu. (23.5 14.3 kg/mg) 7
Methods for Improving Irrigation Efficiency Scheduling Crop water use curves Checkbook Method ET based schedulers Soil Moisture Monitoring Crop Stress/Crop Canopy Temperature Application Efficiency Sprinkler/emitter uniformity Nozzle Type, Spacing, mounting location Calibration Fertigation 8
Crop Water Use (in/day) ET and Growth Stage Soybeans 0.6 0.5 Germination and Seedling Germination and Seedling Reproductive Activity Flowering Podding Seed Fill Maturity 0.4 0.3 0.2 0.1 0 10-Apr 10-May 9-Jun 9-Jul 8-Aug 7-Sep 7-Oct Date
Crop Water Use (in/day) ET and Growth Stage Corn 0.6 0.5 12 leaf Silking Blister Kernel 0.4 Beginning Dent 0.3 0.2 Maturity 0.1 0 10-Apr 10-May 9-Jun 9-Jul 8-Aug 7-Sep 7-Oct Date
Checkbook Soil Water Balance Beginning soil water balance inches Effective rainfall + inches Net irrigation + inches Crop water use - inches Current soil water balance* = inches * The current soil water balance can be no larger than the available water capacity of the active crop root zone.
Practical Challenges Crop Water Use Curves Many Assumptions Assumes: Consistent daily water use. No accounting for reduced water use (cloudy/cool days) Assumes: 100% of irrigation and rainfall is effective. Typically a problem when irrigating in small frequent amounts. Assumes: Irrigation system is applying according to calibration chart. 50% applying less than 80% of calibration chart 12
Evapo-transpiration Based Irrigation Schedulers Uses weather station data to calculate daily Etref.. Temp, Humidity, Solar Radiation, Wind, Soil Moisture level. Determines crop growth stage based on planting date. Uses standard crop coefficients - KC ETref x KC = Etcrop User enters soil data to determine available water. Can be online based or require daily user input. KanSched, Azsched, Irrigator Pro, Colorado State, DE DIMS, CA CIMIS, MSU, Ag Fleet, etc. 13
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Sandy Loam FC 14%, PWP 9% 18 Managed Root Zone 16
Loamy Sand FC 11%, PWP 7% 12 Managed Root Zone 17
Practical Challenges ET Based Schedulers Many Assumptions Assumes: Daily crop water use rate will continue. Future water use forecast relies on past ET rates. Assumes: Uniform soil type, available water capacity across field. Uniform soil profile Assumes: Irrigation system is applying according to calibration chart. 50% applying less than 80% of calibration chart 18
System Calibration and Sprinkler Selection 19
The results of over 400 system evaluations in Delaware, found over 50% applied 20% less water than the timer setting charts predicted. 20
Irrigation system evaluation. Grower Magee Farms Farm/System 6 Tower Reinke Date of evaluation November 2, 2010 The system was evaluated by laying out two radial lines of cans, 5 apart, starting from the first tower. Each can is 5 inches in diameter, and they were spaced 10 feet apart. Where possible, the system was evaluated with the end gun operating, with measurements made out to the end of the end-gun s range. The system speed was measured by timing it over a measured distance. Research and Education Center 16483 County Seat Highway Georgetown, Delaware 19947 Telephone: (302) 856-7303 Timer: 32% Pressure: 22 psi at pivot Estimated full circle: 28.16 hrs 2 lines of cans 5 apart 10 ft spacing GPS at pivot. N38 28.016 W75 9.720 Air temperature: 54 F Wind speed: 5 mph A number of performance factors can be measured by such tests. These include the average depth of irrigation applied; whether the system is irrigating uniformly; and whether there are problems with the system, such as parts of it over or under-applying water. Results: Overall Coefficient of Uniformity, CU, (area weighted): 88.2% Line 1 CU: 89.8% Line 2 CU: 89.2% Average irrigation depth (area weighted): 0.35 inch Flow Meter Readings GPM: 525 Pipe Thickness:.119 Average flowrate measured by can test: 531 Flowmeter versus measured percentage: 99% Manufacturers predicted flowrate: 600 A chart of measured irrigation depth along the system is shown on the next page. Also included is a chart showing irrigation depth as it would vary with timer setting, based on the measured irrigation depth, along with the depth specified by the manufacturer. Comments: A typical CU for a center pivot that is operating well should be within the range of 85% to 92%. The measured CU of 88.2% is good. There appears to be a lower flowrate than the system was designed for, this is also reflected in the 22 psi operating pressure versus the 39 psi design. The measured irrigation rate was less than the manufacturer s chart predicted. Please use the attached measured timer setting chart vs. irrigation rate for the future management of this system. Overall, this system should receive a grade of B+. Items that require immediate attention: Leak at overhang For questions or comments regarding this evaluation, contact James Adkins (302) 856-2585 ext. 588 or adkins@udel.edu.
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An irrigation system can only apply fertilizer as uniformly as it applies water.
Select Sprinkler Package for Field Conditions Consider: application efficiency sprinkler spacing diameter of throw instantaneous application rate/soil infiltration rate peak application rate potential for runoff, soil type/topography
Estimated Water Application Efficiencies Sprinkler/nozzle Type Application Runoff Efficiency Potential High Pressure Impact 80-85 Low Low Pressure Impact 82-85 Low Pressure Spray (on top of pipeline) Low Pressure Spray (truss rod height) Low Pressure Spray (3-7ft off the ground) Low Pressure Spray (LEPA bubble mode) 85-88 87-92 90-95 95-98 High
Peak Application Rates 8.0 7.0 6.0 5.0 4.0 3.0 2.0 1.0 System Length = 1300 ft Flow Rate = 800 gpm Water Application = 1.0 inch Low Pressure Spray Rotating Spray Low Pressure Impact High Pressure Impact 0.0 0 12 2 36 48 60 72 Water Application 4 Time (min)
Canopy Generally Reduces Wetted Diameter and Increases Application Rate
Drops get hung up on crop Non-horizontal Water Application Pattern
In-Canopy Water Distribution Pattern Corn Height 8-10 ft. Nozzle Spacing 12.5 ft Nozzle Height 42 in. Change in Soil Water Content, % 12 8 4 0 2 4 6 8 10 12 14 16 18 20 Row Number
Soil Moisture Sensing 35
Depths of Sample Soil and Root Zone Dependent For sandy loams 15cm, 30cm, 45cm are sufficient On deeper soils, some go to 90cm even 150cm Logged sensors 3 depths and 1 site per 15 ha. 2 sites minimum per field Log frequency 4/day minimum Non-logging 2 depths, 1 site per 10 ha. Sample 1 per week minimum
Soil Moisture Measurement with a Non-Logging Instrument can give misleading information
15cm 30cm 45cm 9mm 6mm 6mm 6mm 9mm 6mm 6mm 6mm 13mm 7mm 32mm 13mm 6mm Silking Blister Milk
15cm 30cm 45cm 10mm 10mm 10mm 10mm 10mm 11mm 14mm 6mm 9mm 25mm Dough Dent
Soil Moisture Sensing Advantages Actual value Not an estimate Does not require accurate rooting depth determination Functions with an improperly calibrated irrigation system Runoff, canopy evaporation, leaching accounted for Disadvantages Expensive Time Consuming Requires precise site selection Difficult to forecast future demands 41
The Ideal Management Tool Meteorological Forecast ET Scheduler Soil Moisture Level Real Time Irrigation Recommendation Fertigation Plan 42
Thank You James Adkins University of Delaware Carvel Research and Ed. Center Georgetown, DE 19947 302-856-7303 adkins@udel.edu 43