Irrigation Scheduling. Irrigation Scheduling Checkbook Method. Think of your soil as a bank. www. msu.edu

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1 Think of your soil as a bank Irrigation Scheduling Lyndon Kelley MSU Extension/Purdue University Irrigation Management Educator www. msu.edu - find St. Joseph Co. - then hit the Irrigation button Water holding capacity: The soil (bank) can hold only a given volume of water before it allow it to pass lower down. Rooting depth: The plant can only get water to the depth of it s roots. Soil type : Heavier soil can hold more water / foot of depth than light soils Intake rate: Water applied faster than the soil intake rate is lost. Evapotranspiration: Removal of water by plant and evaporation Deletion: Plants can pull out only 30-60% of the water Thanks to Dr. Ted Loudon - MSU Ag Engineering Dr. Ron Goldy - MSU Extension Dr. Jeff Andresen MSU Geography Dr. Steve Miller - MSU Ag Engineering Water lost from the bottom of the profile can wash out (leach) water soluble nutrients and pesticides. Irrigation Scheduling Checkbook Method Calculating Water Holding Capacity Soil Name Depth Inches Available water holding capacity Average Available water holding capacity Ave. Available water holding capacity ( 24 in.) Ave. Available water holding capacity ( 36 in.) Tracy Brems x 0.14 = x 0.15 = = x 0.08 = x 0.07 = = x 0.14 = x 0.15 = x 0.13 = x 0.08 = = x 0.08 = x 0.07 = =

2 Think of your soil as a bank Water holding capacity: Soil type : Rooting depth: Evapotranspiration: Removal of water by plant and evaporation Deletion: Plants can pull out only 30-60% of the water Water Quantity Needed Irrigation water replaces the plant water use (removed from soil) Water use is directly correlated to light interception 50% light interception results in about 50% of the maximum water use Maximum water use mid-july early August, full light interception, highest temperatures and brightest days. Intake rate: Water lost from the bottom of the profile can wash out (leach) water soluble nutrients and pesticides. Evapotranspiration (ET) = fn (net radiation) + fn (temperature) + fn (wind speed) + fn (air humidity) Weighing Lysimeter Rain and Irrigation increase weight Evapotransporation decrease weight Alfalfa Corn Soys Field beans Potato Alfalfa Field beans Soys Corn From Minnesota Extension bulletin Irrigation Scheduling, assuming temperature actual evapotranspiration = reference ET * crop coefficient * soil dryness coefficient. aet = ETr * Kc * Ks 2

3 Drip and Trickle Precise application of water to a specific area. Excels where irrigating a portion of field is desired. Excels where watering only the root is desired or when total root saturation of soil is not achieved. Drip_Irrigation_&_Watering_Web_Links.pdf Trickle Irrigation in the Eastern United States NRAES-4, $6 Converting acre inches to gallons for trickle irrigation Calculate the % of area covered by the plant (% of area you intend to water / plant) One acre = 43,560 sq.ft. One acre inch = 27,154 gallons Example: The plants you are watering have a diameter of 6.5 ft. 6.5 ft. x 6.5 ft. = 42 sq.ft. roughly 1/1000 of an acre 26 to 27 gallon / tree = 1 of irrigation (include uncontrolled grass or weed area that is watered in plant area) example 1/1000 of an acre, 27 gal = 1 application 10 x x x x 6.5 Three factor reducing effective water application 1. Irrigation Runoff (comparing irrigation application rate to soil infiltration rate) 0-30 % loss 2. Lack of system uniformity 5-35% loss in effectiveness Sprinkler overlap with end gun 3. Evaporative loss to the air Minimal loss in our humid area 0 6% Estimated 4-6% loss in Nebraska Trickle spacing and soil volume available for water Quantity Needed Drip Irrigation 7/10/1996 Hours to Run Irr at 10 p.s.i. to apply 'X' inches of water: Drip Tape Bed Spacing 0.5 (HH:MM) Hardie Bi-Wall 18" x 72" 6 ft. 1:45 3:35 5:20 7:05 8:55 7 ft. 2:05 4:10 6:15 8:20 10:25 Maximum water use for most crops is in./ day 3 gal/minute/acre pump capacity = 1 /week Netafim.38 gph, 12" +.60 gph, 18" 7 ft. 0:35 1:05 1:40 2:15 2:50 Roberts.24 gph, 12" 5 ft. 1:20 2:40 3:50 5:10 6:30 6 ft. 1:35 3:05 4:40 6:15 7:50 7 ft. 1:50 3:40 5:25 7:15 9:05 Example calcuation for Roberts 24 gph/100 ft. 6 ft. bed spacing: 7260 lbf/a or 72.6 hundred feet 72.6 hundred ft./a X 24 gph/hundred ft. = 1742 gph/a (1742 gph/a) / gal. per acre-inch =.0642 acre-inch per hour For 5 ft. bed spacing, 2091 gph/a =.077 acre-inch per hour 5 gal/minute/acre pump capacity =.25 in./day 7 gal/minute/acre pump capacity =.33 in./day, 1 every 3 days 500 gal/minute pump can provide 1 every 4 days on 100 acres 3

4 Can you Irrigate every hour you want? Limited Water Supply Irrigation Management Diversify the crops sharing the water supply between high and low water use. Stagger planting date to stagger peak water need times. Plant part of irrigated area to a sacrifice crop to neglect during extended drought. Start irrigating early to bank water ahead. Stagger forage crop cutting dates to avoid simultaneous peak use. Think of your soil as a bank - Inputs Rain Gauges Effective Rainfall Water holding capacity: Rooting depth: Effective Irrigation Evapotranspiration: Removal of water by plant and evaporation Plant Wilt Point Basic unit 2 inch opening Cost less than $10 One rain gauge for each 40 acres Recording rain gauge cost $50 - $100 Water lost from the bottom of the profile can wash out (leach) water soluble nutrients and pesticides. SW 1/4 corn ICLIMATE.ORG Available Jun 21 Jun 22 Jun 23 Jun 24 Jun 25 Jun

5 ICLIMATE.ORG Michiana Irrigation Scheduler: Purdue Agronomy web site Est. From High/Low temp. & date Michiana Irrigation Scheduler out put Irrigation Scheduler Checkbook 5

6 Irrigation Scheduler Checkbook Irrigation Scheduling Checkbook Challenges Errors will accumulate over time -Weekly ground truthing needed?? Soil Moisture?? Rainfall variability is more than often considered Only "effective rainfall and irrigation should be considered - Only water entering root zone uniformly is "effective Corn crop mature in program by calendar, not heat Measuring Soil Moisture Tensiometers and Watermarks Measure soil tension - centibars Volumetric Probes TDR FDR Capacitance Probes Moisture by Feel Tensiometers and Watermarks Volumetric Moisture DEVICE Qualitative evaluation of soil water monitoring devices. NP TDR GS AP AQ TM GB WB INITIAL COST FIELD SITE SETUP REQUIREMENTS OBTAINING A ROUTINE READING INTERPRETATION OF READINGS ACCURACY MAINTENANCE SPECIAL CONSIDERATIONS COMPOSITE RATING A score of 1 is least favorable while a score of 10 is most favorable. NP - Neutron Probe TDR -Time Domain Reflectometry GS - Gravimetric Sampling AP - Troxler Sentry 200-AP AQ - Aquaterr Probe TM - Tensiometer GB - Gypsum Block WB - Watermark Block 6

7 Monitoring soil wetted front -12 hrs. after irrigation ½ into dry soil ½ into moist soil 1 into dry soil 1 into moist soil If your 1 application did not go down as far as it did last week??? - your irrigation is not keeping up. Scheduling by comparison Irrigated portion of field should look better than the dry corners/ area Over water observation area should not look significantly better than the adjacent irrigated portion of field. Probe and compare: Dry corners Over irrigated Normal irrigated field Soaker hose attached at pivot point 100% higher output sprinkler 7

8 Assure the best plant stand possible Irrigate, if necessary, to make sure to get maximum germination and uniform emergence. ½ inch in most irrigated soil within five days of planting. Maintain a moist surface,0.10 to 0.20 applications, till spike. Keep the plant growing into moisture. Are you ready to irrigate the day you plant? Using irrigation to get the most from pesticides and nutrients Timely application of irrigation water: Improves incorporation of herbicides. Improves activation of herbicides. Improves activation/reactivation of insecticides. Reduces nitrogen volatilization. Maximizes yield to utilize the resources. Think of your soil as a bank Water holding capacity: The soil (bank) can hold only a given volume of water before it allow it to pass lower down. Soil type : Heavier soil can hold more water / foot of depth than light soils Intake rate: Water applied faster than the soil intake rate is lost. Rooting depth: The plant can only get water to the depth of it s roots. Deletion: Plants can pull out only 30-60% of the water Water lost from the bottom of the profile can wash out (leach) water soluble nutrients and pesticides. 8

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