Richard Taylor, Extension Agronomist; rtaylor@udel.edu
For a number of years, the spring decision of whether to split the nitrogen (N) applied to wheat was often controlled by the price of wheat. When wheat prices were four to five dollars or less per bushel, the return on investment for split N applications was either barely at the breakeven point or below it. Wheat prices this year could encourage growers to again consider if the yield gain, generally about 5 to 7 bu/A, and the environmental and economic impact of less N applied at a single application and subject to leaching, volatilization, and denitrification losses will be enough to incur the risk associated with trying to time and succeed in applying a second N application.
Another factor to consider is whether fall N was applied or if there was adequate residual N available following the previous year’s dryland crop. Even on irrigated ground, residual N could have been present to give the fall planted wheat an excellent start on tiller development. Where an irrigated corn crop was fertigated with N up until tasseling or in fields where a legume crop (soybean or lima bean) was grown, adequate residual N was likely present to give wheat a good start on growth and development.
For fields that didn’t receive fall N and there was unlikely enough residual N present for good fall growth and development, an early application of N at first green-up is critical to obtain maximum tiller production and good yield potential in a small grain crop. In such a case, a split application not only can improve yield potential but can also protect the grower from the loss of a large portion of a large single early application of N due to weather events.
In a four year study in New Castle County that Bob Uniatowski, Research Scientist at the University of Delaware, and I conducted, we found that for high yield wheat a 40 to 60 lb N/A first application followed by a second 60 lb N/A application (total of 100 to 120 lb N/A) was sufficient for maximum economic yield (MEY). The first application occurred between February 15th and March 15th depending on the weather and when wheat green-up occurred. The second application occurred when the tillers assumed an erect position just prior to the first node being visible above the soil surface. For the more typical 60 to 90 bu/A yield potential crop, a split of 40 to 60 lbs N/A at green-up followed by 20 to 40 lb N/A at Feekes 4 to 5 (total of 80 lb N/A) produced MEY.
With the excellent price for wheat this year, the typical yield increase seen with the split of N into two applications, and the potential environmental benefit associated with a lower N application rate at a single point in time, I would encourage all growers to consider this option for maximizing your profitability in 2011.