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Applying nitrogen with irrigation water: Chemigation

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Here, we outline the factors that farm managers who irrigate need to consider before starting nitrogen chemigation. This includes irrigation systems, safety devices, calibrations and more.

A chemigation user permit must be obtained from Minnesota Department of Agriculture (MDA) and safety devices installed to apply N.

Basics of nitrogen chemigation

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Irrigation systems

Apply nitrogen with irrigation water only with systems that can uniformly apply water over the entire field and at an application rate that doesn’t exceed the soil’s infiltration rate. Distributing injected N through an irrigation system is no better than the same system’s distribution of water.

An irrigation system that causes water movement down the plant rows is exceeding the soil intake rate and will not provide adequate N distribution. This situation may cause some N to either leach into the groundwater in areas with water ponds or move into surface water by runoff.

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Nitrogen application guidance

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Calibration

Chemigation calibration is very important to assure the desired amount of N is uniformly distributed over the irrigated field. It’s also very helpful in determining the best injection meter and supply tank size for the given irrigation system.

Several factors are involved in calibrating an injection meter (e.g., positive displacement pump or venturi) for a moving irrigation system like a center pivot. These factors are:

  • Acres covered by the irrigation system.

  • Hours for the irrigation system to cover the acres.

  • Gallons of nitrogen solution required per acre.

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Management tips

For safe, accurate N chemigation, follow these steps each time you apply N:

  1. Check travel time of the irrigation system at the desired water application depth and recalculate the chemical injection rate for the planned amount of nitrogen.

  2. Inspect performance of the check valves, low-pressure drain, low-pressure shutdown switch and all fittings on the chemical supply and discharge hose. Repair all malfunctioning parts before initiating the next chemigation.

  3. Recheck the N injection rate after starting the chemigation process, and adjust if not equal to the planned application.

  4. Periodically revisit the irrigation system and recheck the operation of the injection meter, system operating pressure and water distribution of the irrigation system, including the end gun operation on center pivots.

  5. At the end of each N application, continue running water through the irrigation system until all N has been discharged from the irrigation system’s pipeline. This may take 10 to 15 minutes. Also run clean water through the injection meter, chemical discharge hose and check valve. If you're not planning to use the chemigation system again during the growing season, remove any leftover N from the supply tank or relocate the tank at least 150 feet from any water source (unless it’s in the required containment unit).

  6. If an accident occurs, take action to keep the potential spill to a minimum and immediately report the incident to the MDA at 1-800-422-0798.

Carl Rosen, Extension specialist in nutrient management

Reviewed in 2018

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