Effect of post-emergence nitrogen application on the yield and protein content of wheat

Abstract

Post-emergence application of N with wheat is contemplated as a practice for managing risk and reducing fertilizer N costs. An attempt was made to develop a comprehensive agronomic package relating to the practice of post-emergence applications by examining aspects relating to the rates of N, timing of post-emergence applications and products that might be used for that purpose. An extensive database of 49 trials conducted between 1995 and 1998 separated in five experimental plans was utilized to address the above issues. Nitrogen rates of up to 100 kg N ha-1 were employed as soil applied at seeding by side banding (0, 20, 40 and 60 kg N ha-1) plus topdressed (0, 20 and 40 kg ha-1) as post-emergence applications between Feekes growth stages 10.4 and 10.5. The effect of timing was explored in three different experimental designs that included rates up to 100 kg ha-1 applied at seeding or split, so that a post-emergence application of 20 kg N ha-1 was applied at Feekes growth stages 10 and 10.5, or up to 60 kg N ha-1, applied either all at seeding time or 20 or 40 kg N ha-1 at seeding time accompanied by 20 or 40 kg N ha-1 in a post-emergence application at Feekes growth stages 3–4, 6, 10.5 or 11. A number of products (ammonium nitrate, ammonium sulphate, urea, urea ammonium nitrate, Pro N and N serve) were also evaluated for their effectiveness in post-emergence applications. Two distinct trends emerged from all experiments depending on whether application of N at seeding corrected an N deficiency. If N deficiency was corrected by the application rate at seeding then the post-emergence N application increased grain protein concentrations; however, this practice was shown to result in no economic advantage. If N deficiency was not corrected by the N application at seeding, post-emergence applications at late growth stages increased grain protein of wheat at the expense of grain yield. This increase was greater in soils containing soil organic matter (SOM) concentrations less than 5% than those over 5%. Increases in grain protein ranged from 0.7 to 1.5% depending on initial fertilization regime, but they were not sufficient in any of the circumstances to economically compensate for the loss in grain yield caused by insufficient application of N at seeding. The performance of a number of products used for post-emergence application on the protein of hard red spring wheat was mixed with none proving to be consistently superior. Post-emergence application of N to enhance either the grain yield or protein of hard red spring wheat could be effective under high moisture or irrigated conditions; however, this practice represents a relatively high-risk practice under dryland conditions in the western Canadian prairies. Key words: Economics, growth stage, N rates, N products, timing