Corn plants use large quantities of nitrogen (N) to grow and yield. Determining the optimal nitrogen (N) application rate is crucial for maximizing crop yield and profitability. However, choosing the optimal nitrogen application is challenging, as it depends on factors such as soil type, weather, and crop rotation.
Currently, seven land grant Universities in the Midwest use the Maximum Return To Nitrogen (MRTN) to recommend N. This method refers to the N rate that maximizes profit per acre, rather than simply maximizing yield. By using this approach, farmers can better control nitrogen costs while maximizing profitability. For example, with current N and corn prices, the MRTN rate for central Illinois is approximately 168 lb/ac.
Corn will accumulate 65% of the total nitrogen needs by the time flowering begins. In the seedling stage of corn growth through V5 (5 leaf), corn plants have taken in approximately 10% of total nitrogen needed. It may be the most important 10% used because ear size, as well as both rows around and row length, are developing then. A shortage of nitrogen at V5 can cause reduced ear size formation and lessen yield potential, which cannot be reversed as the plant continues to grow.
During the rapid growth stage, or V6 (6 leaf) to V18 (18 leaf), corn will absorb up to 8 pounds of nitrogen per acre per day. If environmental conditions are right, corn plants can grow more than 4 inches per day. A nitrogen shortage at this stage of corn development can result in a significant and permanent yield loss. Look for yellowing corn leaves and any aborted kernels on the ear tips as symptoms of a nitrogen deficiency.
Nitrogen plays a major role for corn production because it is a major component of amino acids which are the building blocks of proteins. Nitrogen will help corn reach its genetic yield potential.
Nitrogen is one of the most expensive nutrients applied in corn production. That is typically due to the quantity of N that corn requires. It makes sense not to over-apply from an efficiency standpoint, but over-applying nitrogen can have a negative effect on yield, too.
Stalk rot diseases flourish in high nitrogen environments and can cause premature plant death and stalk lodging, which makes machine harvest difficult and can cause some grain loss.
It is important to determine the appropriate nitrogen rate based on sound agronomic practices and not to exceed the recommended rate. Going beyond this rate may not result in a significant yield increase and can be wasteful and harmful to the environment.
Once we calculate the N rate we want to apply, it is important to deduct any nitrogen applied as a starter fertilizer and any nitrogen used as a herbicide carrier or irrigation.
Split applications of nitrogen prevents nitrogen losses from leaching and other volatilization issues, and they are more efficient than applying the total amount of nitrogen required as preplant. This time of year, sidedressing nitrogen will soon be completed. However, if you’re injecting nitrogen through a pivot, now is the time to apply so you can reduce your chances of not being able to do so later due to rain.
All in all, it is best to have all of your nitrogen applied to corn before R1 (or silk emergence) because nitrogen applied after that stage is not as efficient and generally has little, if any, impact on your final yield.
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