By Randy Pryor, Extension Educator, Saline County
With the goal of growing the same or more bushels with less water, farmers can calculate their Irrigation Water Use Efficiency (IWUE). This is the number of bushels produced per inch of water applied.
IWUE = (Irrigated yield - typical rainfed yield for your area) / inches of water applied.
IWUE targets should be:
- irrigated corn — 12-14 bushels/inch of water and
- irrigation soybeans — 3.0-3.5 bushels/inch of water.
IWUEs below these “ideal targets” may indicate improvements are needed in management or application efficiency.
Improving Irrigation Efficiency
Each of the following 10 items offer a means for improving irrigation water use efficiency as well as sources for mobile apps and resources to aid in the changes.
- Convert from furrow irrigation to pivot irrigation. Converting from a typically 50% efficient furrow irrigation system to a 90% efficient center pivot system reduces water requirements. Also see Maximizing Pivot Efficiency.
- Perform pivot checks and maintenance. Check your nozzle package against the manufacturer’s nozzle chart to be sure it was installed correctly (do this once) and that the pressure gauge is accurate for operator use in managing the pumping plant setting. Also check application uniformity. For a "how-to" guide see this checklist for maintaining your pivot.
- Use soil water sensors to schedule irrigations and UNL’s CropWater App to monitor soil water depletion and to track available soil water for the season. For more information see Cost Effective Tools to Improve Water Use Efficiency and links from it to information on ETgages and Watermark sensors.
- Use a flow meter and UNL’s MeterCalc App to help manage water use. From your smart phone, you can compare weekly irrigation application to weekly ET (using ET gauge or weather station data and crop stage of growth crop coefficient). Also track season ET and compare it to total irrigation application. The online Irrigation Meter Calculator also can be used to estimate inches of water applied per acre over a given season.
- Reduce soil moisture lost through evaporation. Approximately 30% of evapotranspiration (ET) is evaporation. This amounts to about 7 inches per year in a typical system. To reduce evaporation loss, increase residue on the soil surface by using no-till.
- Increase rainfall and irrigation water infiltration. Using no-till systems and maintaining residue levels on the soil surface increases water infiltration. See more on the benefits of no-till in Switching to No-till and Controlled Wheel Traffic Can Save Irrigation Water and the per-acre savings in Water Savings with Residue Management and No-Till.
- Schedule the last irrigation strategically. Use CropWater App to deplete stored soil water profile, allowing for precipitation storage during the off season. (See Scheduling the Last Irrigation of the Season)
- Determine your pumping plant’s efficiency by comparing it to the Nebraska Pumping Plant Performance Criteria and making improvements where needed. The UNL IrrigatePump App helps producers reduce pumping plant fuel consumption. A pumping plant meeting the criteria is delivering the expected amount of useful work, measured as water horsepower hours (whp-h), for the amount of energy consumed. UNL research has shown many older pumping plants operating at 30%-50% efficiency while newer ones were at 82%-92% efficiency. To learn the per-acre cost savings of this change, see Repair or Replace Inefficient Pumping Plants
- Convert to a low pressure irrigation system. Typically lower pressure systems aid energy conservation and reduce droplet and leaf surface water evaporation; however, they also may generate runoff.
- Reduce transpiration that doesn’t produce yields. Allow some water stress during vegetative growth stages and apply full water during reproductive growth stages.
More Resources for Getting More Crop from the Drop
- Surviving High Input Costs in Crop Production shows where you can make adjustments in your farm management, including irrigation management, and the per bushel savings you can expect.