With corn out of the ground, one of our next steps is to get layby nitrogen on the crop. Nitrogen seems to be in good supply but price has gone up on urea, and delivery for some sources has been a little slow due to heavy demand around the U.S. Some things to consider with nitrogen are rate and timing of material and the value of a stabilizer material.
Rate: Total nitrogen needs are based on yield potential of a corn field. In non-irrigated fields unless we have very timely rains, nitrogen use efficiency is lower and we have to apply an average of 1.1 lbs N per bushel of yield. With good corn prices, we can actually afford to spend a little more on N– up to about 1.2 lbs N per bushel of yield, but higher rates of N will probably give you an economic return only in non-irrigated fields where yield potential is good (175 bu or better). Nitrogen use efficiency is better under irrigation- in other words we are able to make more yield per pound of nitrogen applied and it may not be necessary to apply more than 1.0 lb N per bushel of anticipated yield. Based on 4 years of irrigated corn data at Milan, we have made some excellent corn yields with nitrogen rates as low as 0.9 lbs N per bushel of yield.
Timing: Most of our fields have already had some at-planting nitrogen and are waiting for layby. Split-applying nitrogen gives us the flexibility to adjust that final rate in cases of early season nitrogen loss (we haven’t lost much N this year except maybe in fields where there was no rainfall to incorporate at-planting surface-applied material). Apply the majority of N before V-6 corn (roughly by 30 days after planting) to allow time for material to be rained in and to become available to the plant. Irrigation gives us the option of using delayed applictions such as pre-tassel or mid season fertigation. We are gathering data on pre-tassel applications, but based on work done in the midwest, they can be very effective under irrigation where nitrogen needs have not been met prior to pollination.
N Sources and Stabilizers: Although there have been some quality (spreading) issues with calcium ammonium nitrate, most available sources are effective nitrogen materials.
* ESN (Environmentally Smart Nitrogen) and ‘true’ ammonium nitrate are very stable surface materials for no-till corn based on work done by Univ. of Ky. They do not require additional stabilizers but may have more limited use due to supply and cost issues. Leaf burn from ammonium nitrate looks painful but doesn’t hurt corn yields. Apply to smaller sized corn, wait to apply when dew has dried off, or irrigate the field shortly after application to reduce plant burn with ammonium nitrate.
* Urea and UAN are more widely used than ever due to the lower cost of both materials and easier availability compared with ammonium nitrate. Injecting or spraying UAN in a narrow band behind a coulter is an effective way of concentrating the material and does not necessarily require a stabilizer. Surface applying Urea or streaming UAN does benefit from a stabilizer unless you can irrigate (minimum of 0.2″ water) or incorporate into the soil within 24 hrs. There are a number of nitrogen stabilizer products on the market but Agrotain has been the most consistent product for urea or UAN based on testing in TN and KY. A stabilizer is not a magic potion- it works for a period of time (generally less than 2 weeks) to reduce surface volatilty loss until a rain event incorporates the fertilizer into the soil. But, effective products like Agrotain do work and should be considered when surface applying Urea or UAN under warm soil conditions.
