Fertigation and sidedress nitrogen applications can protect farm profits and the environment
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EmailSplit nitrogen applications, such as fertigation and sidedress nitrogen, on sandy soils are an essential component to increasing nitrogen use efficiency and mitigating environmental risks.
Nitrogen is an essential element for plant growth and is required in great concentrations within the plant for healthy crops and yields. One of the greatest challenges in striving for high yields on sandy soils is holding onto water and nutrients. Nitrogen (N) can be highly mobile in water, so finding ways to increase nitrogen use efficiency and decrease loss protects profits by avoiding the need for additional N purchases and helps protect the environment from N contamination. Nitrogen on soil surfaces can volatilize into the air and contribute to ozone depletion. Nitrates are the leachable form of N and can come from both fertilizer and natural decomposition of living matter. According to the Agency for Toxic Substances and Disease Registry, nitrates in groundwater can cause methemoglobinemia, or blue baby syndrome, a health risk to pregnant women and children four months old or younger. In addition to the environmental impact, reducing N loss is an economic advantage to growers since N has high cost inputs in the production budget for most crops.
Splitting N applications is the concept of applying multiple smaller applications of nitrogen throughout the season to match the crop uptake of the nutrient. This reduces the risk of excess N in the soil, which is subject to loss. Producers applying the total nitrogen needs for the year in a single application before planting are at the greatest risk of losing nitrogen. Producers with two or more splits of nitrogen spread from planting through early July run a much lower risk of losing any large portion of the N. The N-use curve for most crops follows the rapid growth of the crop. Corn, our most common irrigated crop, has its greatest uptake of nitrogen starting between V6 and V10 and going through tasseling. As with any application, producers should plan ahead to effectively manage nitrogen. The Michigan State University Soil Fertility Research website and the Michigan State University Extension Field Crops Virtual Breakfast videos have many resources for nitrogen management in corn.
Sidedressing nitrogen
Three common sidedress application systems are used in Michigan and Indiana: anhydrous ammonia, injecting liquid fertilizer and broadcasting dry N forms. Anhydrous ammonia, dry formulations and liquid formulations all benefit from a timely rainfall or irrigation application to incorporate them into the root zone. Unlike fertigation, sidedressing is often done only once, as the economic return from multiple sidedresses is low, and risk for crop damage increases as the crops progress.
Anhydrous ammonia (NH3) is a highly concentrated form of N that aggressively seeks out water in the soil when injected under the surface. The application of anhydrous ammonia has declined over the last few decades due to the extremely dangerous health risks and precautions required to use the product. The benefit of anhydrous ammonia is the high concentration, keeping the transportation cost comparatively low compared to dry and liquid N fertilizers. Anhydrous ammonia is relatively non-leachable until it is converted by bacteria to a nitrate form, which offers a slow-release curve tied to temperature, helping it match crop use.
A liquid formulation commonly used for sidedress application is urea ammonium nitrate (UAN) 28-0-0 or 32-0-0. An injection disk, knife or pressure injection must be used to force the liquid under the soil surface with minimum exposure to foliage. Otherwise, these liquids will cause foliar crop injury and potentially reduce yields. The injection under the soil can help reduce N loss to the atmosphere.
Dry formulations commonly used for nitrogen fertilizer at sidedress are urea and ammonium sulfate (AMS) or combinations of both. Because these are applied to the soil surface, they are especially susceptible to loss through volatilization. It is critical to apply shortly before rainfall or use irrigation to water the fertilizer in. For corn in early vegetative stages, ground applicators can be pulled behind tractors with narrow tires to broadcast the fertilizer. Once crops are above knee high, most will require applications to be made with highboy tractor systems. Although much more costly per acre, aerial applications are another option, usually when wet weather or rapid growth keeps other systems from being used.
Fertigation
Fertigation is the application of fertilizers through irrigation water. Unlike sidedresses, multiple fertigation events are likely to provide a higher economic return. Fertigation allows producers to “spoon feed” the crop. These multiple small applications allow irrigators to modify their N management throughout the whole season to respond to commodity and fertilizer price changes. The additional cost of each pass with field equipment and potential damage to the crop limits most producers to a single sidedress application. Liquid formulations of nitrogen fertilizer such as UAN 28-0-0 provide a source of N that can be applied with the irrigation water. Other products can supply sulfur and some micronutrients in addition to N. Fertigation is an increasingly common portion of nitrogen management plans for irrigated farms (especially on sandy soils), providing the final increment(s) of split nitrogen.
The inherent risk of injecting fertilizer into a water system dictates the requirement for backflow protection. Both Indiana and Michigan have resource protection rules that require using chemigation valves for the protection of both surface and ground water sources. According to Generally Accepted Agricultural and Management Practices (GAAMPs) for Irrigation Water Use by the Michigan Department of Agriculture and Rural Development (MDARD), “a chemigation valve contains a functional
check valve, vacuum relief valve, and a low-pressure drain.” This creates an air gap downstream from the pump when the pump is shut down. The air gap breaks the suction created by returning water and prevents contaminants from entering surface or ground water. Chemigation valves, for most irrigation systems, are available from local irrigation dealers for less than $700. Installation cost is much less at the time of pump construction and should be included in almost all new installations.
Detailed information on injection pumps, backflow protection, safety interlocks and procedures for calibrating an injection system is available in Michigan State University Extension bulletin E-2099, “Using Chemigation Safely and Effectively.”
To reduce health and environmental risks, producers applying nitrogen need to make sure that as much of it is taken up by the plant as possible. On sandy soils, particular care should be taken to reduce the risk of leaching. Nitrogen on the soil surface can also be lost to the atmosphere, which poses a different environmental hazard. Improving nitrogen use efficiency and preventing N loss is important for both protecting the environment and profits.
