From a practical standpoint, in order to minimize risk, it would be preferable to apply the nitrogen at GS45 because of the greater opportunity to receive precipitation and the ease of identifying the growth stage. Also we had positive results in both years at GS45 while only in one year at GS69. The other important consideration is the relative economic performance of this management strategy. Table 2 shows gross and net returns for different initial rates of fertilizer and different foliar application times for the two soil types. Gross returns are determined by yield and price for the particular protein level.
Net returns are gross returns minus the fertilizer cost for that treatment.
Generally, foliar nitrogen application at GS45 showed the best net returns on both soil types which initially had low to average fertilizer applied. Application at GS69 and on treatments with higher initial application of nitrogen produced more variable results. On the crop side of things, a good estimate of the yield potential just before GS45 would have to be made and the decision would also have to take into consideration the amount of nitrogen applied prior or at seeding and some estimate of the nitrogen supplying power of the soil. The soil's ability to supply nitrogen would be influenced by factors such as crop rotation and previous use of nitrogen fertilizers. The effects of foliar applied N on grain yield and grain protein concentration at different rates of nitrogen in spring wheat in 1994 and 1995 at two locations.