Nitrogen is the most limiting nutrient in corn production. Applying sufficient amounts of this nutrient is as critical as fertilizing at the times where the needs are highest.
When a corn plant is at the V3 stage (2-3 weeks after planting), the number of leaves and ear shoots are being determined. By the time the plant reaches the V5 stage, which occurs about 4-5 weeks after planting, and plants are normally 18-24 inches, the growing point and tassel are above the ground, and the plant becomes much more susceptible to stresses.
At the V6 stage, proper and sufficient fertilization is critical as plants will experience a rapid rate of growth. The number of rows per ear is established around this time, and the lowest two leavesmay no longer be present. Fertilization can wait until the V8 stage without negative consequences, if some nitrogen was applied preplant. However, if no nitrogen has been applied at all, yield losses are possible if the fertilization is delayed until V8. Splitting the application of N can be seen as an option to reduce the cost associated with current urea prices, but consider the following: 1) the time between V6 and V8 is probably no more than 1 week to 10 days; 2) it may take a corn plant several days to weeks before it can use all the nitrogen applied at V6; 3) with each growing stage developing every 3 days, it means that a corn plant at the V6 stage may take only 4-5 weeks more to tassel. Consequently, corn planted in March is probably near the V6 stage, so waiting for lower urea prices to fertilize may be a risky option. Reducing the application rate by 10% or so will probably have no negative consequences on yield potential. Farmers may consider the use of proven urease inhibitors to reduce the risk associated with potential volatilization losses.
Under most conditions, all nitrogen sources perform with the same efficiency. Given current fertilizer prices, farmers should consider sources that result in the lower price per unit of fertilizer. The table below shows the amount of nitrogen per ton, or pounds of N per gallon where applicable, for the most common nitrogen sources.
|Fertilizer||Lb N/ton||Lb N/gallon||Price per unit of N||Lb sulfur/ton|
|UAN 28%||560||3.1||.80||May contain 100 lb|
|Calcium ammonium nitrate||540||NA||.92||None|