Spring Nitrogen Applications

Actual nitrogen (N) use by corn and N loss from the root zone can vary from year to year. Nitrogen is one of the most expensive and difficult inputs to manage.

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Table 1
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The major crops remove substantial amounts of nutrients during the season (Table 1). Estimating nutrient removal during fertility program planning can help ensure that adequate amounts of nutrients are available for optimum yield production.

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Spring sampling for soil nitrate-nitrogen (up to 6 to12 inch corn) can help determine the soil N status after the winter. The information can be used to plan spring preplant, at-planting, or sidedress applications. Early planting and later season N needs for modern corn products increases the need to consider in-crop supplemental N. In many situations, fall or spring preplant N applications are well ahead of periods of rapid corn uptake and susceptible to loss if warm temperatures and excessive rainfall occur early in the season. At planting and sidedress N applications can provide N closer to periods of uptake by the plant. Corn needs one-half of the total N requirement during the V8 to tasseling stage of growth and one-third during the reproductive stages of growth (Figure 1). From flowering to maturity, corn products can take up from 30% to 40% of their total N, over 50% of their total phosphorus (P), and over 40% of their total sulfur (S) at maturity.

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Figure 1

Figure 1. Seasonal nitrogen uptake in corn. Graph courtesy of Bender, R. University of Illinois Crop Physiology Lab.

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At-planting applications such as starter fertilizer applied with the planter can be used to supply N, P, K (potassium), S, and Zn (zinc). Recent research has shown early growth and yield benefits for P, Zn, and S on many soils in the region. Starter N can help hedge against weather delaying an in-crop application.

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Sidedress applications (V5 to V8 corn) to provide a portion of the total N needed by the crop should be part of a fertility plan that has the majority of N applied in the fall or spring prior to corn planting. The risk with sidedressing is that conditions may delay the application and corn gets too tall to avoid breaking stalks or damaging roots. Consider sidedress for fields that are prone to denitrification or leaching loss. Speed of application will be influenced by the size of the applicator, N source, soil conditions, row spacing, and size of the corn. The soil nitrate test can be used to determine rates of N rates for sidedress application.

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Nitrogen Advisor. As planting season approaches, the amount of fall applied and residual N within reach of corn roots should be evaluated. One means of evaluation is utilization of the Climate FieldView™ Pro Nitrogen Advisor analysis program. The program continually collects environmental information such as rainfall and temperature on each field. Anhydrous application dates can then be input into the system and N loss estimated based on the environmental information. Individual fields can also be edited to customize the advisor results for a farmer’s operation to assist in planning and monitoring for the entire year. A Nitrogen Advisor overview screen has also been added to help farmers identify which fields need the most attention and which fields may be at-risk for missing yield potential targets. To learn more, visit www.climate.com.