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Nitrogen Recommendations for Corn

Corn is probably the crop that uses the largest amount of nitrogen, due in part to the amount of biomass produced by a corn crop. Additionally, the low levels of organic matter in our soils require that most of the nitrogen comes from chemical fertilizer.

Current nitrogen recommendations for corn are based on yield goal and soil texture. With urea prices breaking the $800 per ton, it is very important to revise fertility programs to avoid unnecessary expenses. The table below shows the nitrogen rates, which range between 150 and 255 lb/acre, for silt loams and between 230 and 330lb/acre for heavy-textured soils, depending on selected yield goal.

Table 1. Nitrogen recommendations for corn based on soil texture and yield goal.
 

Yield Goal (bu/acre)

 

125

150

175

>200

         
Soil Texture

N rate (lb/acre)

Silt and sandy loams

150

185

220

255

Clay loams and clay soils

230

280

330

330

Nitrogen fertilizer recommendations are meant to be a guide for a farmer to fine tune based on his particular growing conditions, keeping in mind that there are several factors other than fertility, that can affect yield potential. Those farmers who have been growing corn for several years may have a good idea of how much nitrogen they need to apply to obtain consistent corn yields in specific fields. Farmers who are new to corn should know that our recommendations tend to be conservative in nature. While we may recommend 255 lb N/a for yields of 200 bu/A, similar yields can probably be obtained with lower amounts of fertilizer but under higher nitrogen use efficiency.  Nitrogen is perhaps the most difficult nutrient to manage because it is the most affected by weather conditions. In fact, nitrogen use efficiency is probably no more than 50% of the fertilizer applied. This does not mean we are applying excessive amounts of nitrogen, but rather that our growing conditions may require larger amounts of chemical fertilizer than in other regions.A quick review of the nearly 3,000 “corn” soil samples sent to the lab in the months of February and March showed that 69% of the samplers selected a yield goal of 200 or more bu/a. While we hope that 7 out of 10 farmers get yields around 200 bu/acre this season, the reality is that most of our corn yields will probably be around 175 bu/acre. Arkansas’ corn yield average in 2011 was 145 bu/acre, but this average includes dry land corn.

Current nitrogen recommendations for corn grown in clayey soils call for as much as 330 lb N/acre. However, on-going research supported by the Corn and Grain Sorghum Board has shown that yields can probably be maximized with an average of 270 lb N/acre.  Results show that on an average, when nitrogen was applied at 200 lb/a, 84% of yield potential was observed; when 250 lb/a were applied, 94% of yield potential was observed; and 97% of yield potential was observed when 300 lb/a N were applied.  Based on these results, the optimum rate for corn grown in clayey soils should be in the 250-300 lb/a range. Maximum yields in these studies have varied among locations and years, but have oscillated between 175 and 220 bu/a.

We suggest that the nitrogen be applied in 2-3 way split to increase use efficiency. One option is to apply 20% of the rate pre-plant; 60% around the V4-V6 stage, and the remainder 20% one week before the tassel emerges—the pre-tassel split applies to yield goals larger than 150 bu/a . It is estimated that between emergence and the V4 stage, a corn plant has used less than 10% of its total nitrogen requirement, with the largest need occurring soon after the growing point is above ground; so applying a large amount of nitrogen pre-plant is not very efficient.

Producers should use only proven technologies to reduce loss potential. Under extended wet periods, nitrogen can be lost by leaching or denitrification. However, under dry periods or inability to properly incorporate urea, nitrogen can be lost as ammonia gas. At this moment, the University of Arkansas recommends only NBPT-based products as an effective means to reduce ammonia volatilization risks when urea is not properly incorporated. While most are familiar with AGROTAIN, there is a new product in the market called Arborite. Both of these products contain NBPT and when applied based on the manufacturers’ recommendations, they have been effective at reducing ammonia volatilization losses for 10 days or so.

 


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