Fertigation: A midseason option for fertilizer application to irrigated fields
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EmailApplying fertilizer through irrigation, also known as fertigation, allows irrigators to apply the last increment of nitrogen to their growing crops.
Your fields may have lost part of their nitrogen to water through denitrification, through nitrates moving below the root zone following heavy rainfall, or by simply having the crop grow so fast that you missed the sidedress window. Either way, some fields may need additional nitrogen to reach yield goals. You can contact your local Michigan State University Extension county office for information on estimating nitrogen loss from your fields, but if your field is irrigated, you have options to replenish nitrogen.
Chemigation is a term for adding fertilizers or pesticides to irrigation water. Fertigation is a subset of chemigation specific to adding fertilizer to irrigation water. Irrigated production has the advantage of fertigation as an option in nitrogen management. Liquid 28% nitrogen is the most common product for fertigation, but combinations of urea ammonium nitrate, ammonium thiosulfate and micro-nutrient solutions are also available to meet crop nutrient needs through irrigation.
Fertigation is often the last step in a three-split nitrogen management plan following starter and sidedress applications. Starter allows quick access to nutrients for the newly germinated plants. Sidedress applications usually account for the greatest portion of the nitrogen budget, feeding the plant just prior to the rapid growth phase. Depending on the equipment used, sidedressing can also aerate soil and improve water infiltration.
Fertigation makes up the remainder of the budget, supplying nitrogen to the crop just prior to tassel emergence. For efficient use, nitrogen applications need to be made prior to tasseling or soon after to ensure the nitrogen applied is in an available form for the plant to uptake and use during early grain formation.
From a management standpoint, fertigation allows producers to evaluate crop stands, nitrogen losses due to wet conditions or heavy rain, and the current market situation in order to make adjustments to the nitrogen plan to meet the crop's needs and maximize profitability.
As an example, let’s say you have a 210-bushel yield goal on an irrigated field that calls for 230 pounds of nitrogen. At planting, you apply 30 pounds of nitrogen, followed by 120 pounds applied at cultivation in early June. No nitrogen credit is given because of sandy soils and the continuous corn production. This leaves a nitrogen need of 80 pounds. You decide to apply the remaining 80 pounds, split into two 40-pound applications through the irrigation system. We get about 3.1 pounds of actual nitrogen for each gallon of 28% nitrogen applied. You calculate that you need to apply just short of 13 gallons per acre. Knowing that your system irrigates two acres per hour, you calculate that you need to inject 26 gallons of fertilizer per hour.
Knowing the actual amount of fertilizer the equipment will inject is essential. It is also important to know that the system applies water uniformly across the field. Center pivot systems of good design will have a uniformity coefficient of greater than 85%. It is important to remember that the application uniformity of the nutrients will be no better than the water uniformity of the system. When the application is 50% over or under the average application amount, the system is malfunctioning. The desired 40 pounds nitrogen application may instead be 60 pounds in some areas and only 20 pounds in other areas.
Learn more about improving irrigation center pivot uniformity from the Michigan State University (MSU) Extension resource, “Evaluating Irrigation System Uniformity.”
Suggested minimum performance for chemigation/fertigation:
- Pivot point and last sprinkler pressure within 10% of sprinkler package specifications
- Required backflow protection in place and functional
- No major leaks or repairs needed
- No major runoff issues
- Capable of applying 0.25 inches or less for fungicides
- No 2X or greater overapplication
The inherent risk of injecting fertilizer into a water system dictates the need for backflow protection. Indiana and Michigan have resource protection rules that require using chemigation valves for the protection of surface and groundwater sources. Chemigation valves create an air gap in the pipeline downstream from the pump when the pump is shut down. The air gap breaks the suction created by water and retreats to groundwater or surface water. Chemigation valves for most irrigation are available from local irrigation dealers for around $700. Installation cost is much less at the time of pump installation and should be included in almost all new irrigation pumping installations.
To avoid the loss of nitrogen, make sure there's enough available water holding capacity in the soil profile to hold the application volume. One of the simplest ways to accomplish this is to estimate the days of water removal required to make available space for the fertigation application. If crop water use is 0.15 inches per day, waiting four days (0.6-inch removal) from the last rainfall should assure you have the capacity to hold a 0.5-inch fertigation application.
In some situations, producers may choose to dribble or broadcast nitrogen on the field by air or using a high-clearance sprayer and use the irrigation to incorporate the nitrogen if dry weather follows. This technique is quick, requiring no irrigation equipment modification, but is dependent on the availability of aerial applicators or in-row high-clearance application equipment.
Detailed information on injection pumps, backflow protection, safety interlocks and procedures for calibrating an injection system is available in “Using Chemigation Safely and Effectively,” MSU Extension bulletin E2099. You can also download this Chemigation/Fertigation PowerPoint presentation from MSU Extension and Purdue Extension for more information.
Special thanks to Bruce MacKellar, MSU Extension field crops educator, and Steve Miller, MSU Biosystems and Agricultural Engineering irrigation specialist, for their input into this article.
