Nitrogen Optimization

Managing nitrogen (N) fertilization is an important element of input cost control and maintaining optimum yield potential. Timing, rate, source, and method of N application plus N loss mechanisms, all play a role in this balancing act.

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Timing of application can be influenced by factors such as weather and workload. It is desirable to apply N as close to the period of rapid plant uptake as possible so that there is reduced risk of N loss prior to plant use. Sidedress applications are preferred over pre-plant, and pre-plant applications are preferred over fall applications in synchronizing N application to rapid crop N uptake and to limit potential loss.1 To reduce spring N loss when N has been applied more than 2 weeks prior to planting, anhydrous ammonia is recommended.1 When considering in-season N applications, the preferred method is injection of ammonia or UAN, followed by UAN dribbled between rows or broadcast urea.2

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Sidedressing N applications can help supplement a pre-plant fertility program or supply N to the crop if conditions prevented N application before planting. The first step to addressing potential problems is to determine how much nitrate-N has been lost in the soil. Nitrate is the most plant available form of N.

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To estimate how much N has potentially been lost, take into account soil temperatures and days a soil has been saturated. Keep in mind that there will be more nitrate present if there has been a recent application of urea-ammonium nitrate solutions (28, 32% UAN) because one-fourth of the product is nitrate-N.2 Sidedressing N should be targeted for application prior to the V8 stage of growth, when the plant’s demand for N increases rapidly. Adequate N from V5 through V8 is critical because the number of potential ears and ear girth are being determined. Nitrogen sidedress rates are determined by soil nitrate test results.4

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Nitrogen application rates based on yield goals have been a common method to determine the amount of N application.1 University recommendations advise to fertilize for normal yields, even in good years, because under those ideal conditions, the microbial activity leads to soils releasing more N to the crop.1