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Spring Nitrogen Considerations

Categories: GROWING, CORN

Risk and Evaluation of Nitrogen Loss

Pyramid diagram of application factors that can influence the risk of nitrogen loss in soil.
Figure 1. Illustration of factors that can influence risk of N loss.

Due to being highly mobile and having a higher risk of soil loss, corn plants often experience nitrogen (N) deficiencies more often than other nutrient deficiencies. When managed properly, appropriate N levels can result in substantial potential economic returns. Limited opportunities to apply N in the fall and spring often result in re-evaluating management plans in-season. If unable to apply a preemergence N application or if N loss is suspected, there are multiple in-season options that may help minimize potential yield loss. Determining how much plant available N is readily available or still needs to be applied can be difficult to determine. Not all N applied will be readily available to the plant depending on the N form applied, the application method, the application timing and any environmental-driven N loss factors, such as temperature or precipitation.

Color coded map diagram of excessive spring rainfall in 2013 that were more prone to nitrogen loss.
Figure 2. Excessive spring rainfall areas in 2013 that were more prone to N loss. Source: Midwestern Regional Climate Center.

Commonly Used Methods to Identify Nitrogen Needs

  1. Late spring or pre-sidedress soil nitrate test: Soil nitrate levels increase as soil temperatures warm and mineralization rates increase. Soil nitrate mineralization peaks in late May/early June (around V5-V6) making a soil nitrate test at this time from the top 12 inches of soil a good indicator of N needs. Soil test results of >25 ppm are less likely to need additional N.

  2. Crop sensors: Using leaf light reflectance as an indicator for additional N needs has had success. Examples of tools to use include:

  3. N models: Modelling software such as Adapt-N utilizes soil and live weather data in combination with prior crop management practices to estimate if additional N is needed.

Application Timing and Use

description of the nitrogen uptake by the plant type

N demand of corn prior to V8 is relatively low – less than 25 lbs. N/acre. With roughly 10% of the total N typically being taken up by mid-June, most early N needs of corn can be met through mineralization of soil organic matter and prior season soybean residue in corn following soybeans rotations. It is more important to ensure at least a portion of N (around 40 lbs. N/acre) is applied before or soon after planting when planting corn following corn. N demand increases dramatically after corn begins to grow rapidly at the V6-V8 growth stages making it important to have most supplemental N applied prior to this timing. By silking, plants will have absorbed near 70% of the total N needed. Yield potential can decline rapidly if N isn’t available during this critical timing. Corn continues to use significant amounts of N throughout grain fill. Split applications of N can help minimize in-season N loss and improve N use efficiency if applied timely. Split applications can provide even more value in sandy soils that are more prone to leaching and have less opportunity to mineralize N from organic matter. To maximize yield potential and enhance plant nutrient use efficiency, time N application prior to peak uptake

Nitrogen Source Considerations

Anhydrous ammonia:

One of the most inexpensive forms of N available, anhydrous ammonia can be applied late fall, early spring or sidedressed in-season. Delaying fall applications until soils begin to cool (<50° F) is important to minimize loss. Adding a nitrification inhibitor may also greatly reduce loss if excessive spring rainfall occurs as soil temperatures begin to warm. Nitrification inhibitors are not needed when sidedressing in-season, however, poor closure of knife applicators can result in ammonia loss and leaf burning.

Urea (dry):

This form of N can be broadcast pre-plant or over emerged corn with a high clearance applicator at higher speeds to cover more acres per day. Consider using a urease inhibitor to minimize volatilization loss if it is not incorporated into the soil. Timing applications of urea prior to rain events or cultivation after application can help minimize N loss. Anticipate minor leaf burn from urea trapped within the whorl of emerged corn.

UAN (liquid):

This form of N can be broadcast sprayed, fertigated, injected into the soil or dribble-applied between rows. Apply UAN as close to the timing of crop uptake as possible since a portion of it is in the nitrate form which may be rapidly lost if excess rainfall occurs. Broadcast applications can cause leaf burn, therefore, applying UAN to small corn (<V4) and at lower rates is advised unless able to sidedress. Leaf burn usually disappears quickly with good growing conditions. Sidedressing UAN to emerged corn with coulters or Y-drop applicators can reduce crop damage risk and achieve higher N use efficiency.

Product performance assumes disease presence.

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