The Idaho Wheat Commission has identified N fertilization practices as a research need, especially the performance of newer materials. In response to their concern a fertilizer trial was conducted by Extension Educator Chad Cheney in Butte Co near Arco in a pivot irrigated field of soft white spring wheat. The fertilizers included conventional urea, NSN, ESN, and Agrotain treated urea. The N rates used included a zero check and 60, 90, and 120 lb of actual N (or units) per acre. All fertilizers were broadcast by hand to plots and lightly incorporated prior to drilling the wheat with a double disk drill. The previous crop was alfalfa that was disked and ripped in the fall

Pre-plant N evaluated for irrigated spring wheatThe 120 lb N per acre rate gave the highest yield of all treatments, when averaged across N fertilizers, although the fitted yield response curve suggests that a higher N rate may have been necessary to maximize yield Fig. 4. Wheat protein associated with the 120 lb N rate was only 8.5%. Note that the protein tended to increase more rapidly with increased N as the yield began to level off or plateau.

The N fertilizers used at Arco did not differ statistically from each other in yield, despite two fertilizers, Agrotain and ESN, that averaged 5 and 7 bu per acre respectively higher than conventional urea. The yield findings mirror the yield results for furrow irrigated spring wheat with N pre-plant incorporated at Parma. Slow release ESN pre-plant incorporated in furrow irrigated spring wheat actually yielded higher than urea at Parma over three years, perhaps because there was greater potential for leaching with conventional urea.

Test weight, protein and total grain protein N averaged higher for ESN than all other fertilizers. Across all fertilizer rates protein averaged 8.5% for ESN and from 8.0 to 8.2% for other N fertilizers. Total protein N measured 119 lb/A for ESN and from 106 to 111 lb/A for other materials. Similar results were obtained at Parma from pre-plant applications of ESN compared to urea.

This study is one of the few Idaho evaluations of N fertilizers under sprinkler irrigated conditions. It represents only one year of study so the results are tentative.