Timing Split Applications of Nitrogen for Irrigated Hard Red Spring Wheat

Split N applications offer the potential for improving yield and quality of irrigated spring wheat (Triticum aestivum L.) while minimizing NO3−leaching losses. Field studies were conducted in 1985 and 1986 to evaluate the effects of N rate andtiming on grain yield, test weight, and protein content of four hard red spring wheat varieties. Thesoil type was a Declo silt loam (coarse‐loamy, mixed, mesic Xerollic Calciorthid). In both years,two N levels (60 and 120 lb N/acre) were applied preplant, or as various combinations of preplantand topdressed N. Top‐dress applications of 30 lb N/acre were made at either stem elongation (Feekesstage 7), anthesis (Feekes stage 10.5), or at both stem elongation and anthesis. The remaining Nfertilizer (0–120 lb N/acre) was applied just prior to planting. Residual soil NO3−‐N plus NH4+‐N was 112 lb N/acre in 1985 and 64 lb N/acre in 1986. All varieties responded similarlyto the different N treatments. Grain yield was not affected by N timing as long as total Navailability was adequate for maximum yield but was reduced when N availability was inadequateduring early grain development and N topdressing was delayed until anthesis. Test weight wasincreased by 0.4 to 0.8 Ib/bu in 1986 by single‐split N applications at anthesis, but was notaffected by N timing in 1985. Splitting N applications increased grain protein content by an averageof 0.5% in both 1985 and 1986. Single‐split applications at stem elongation were generally not aseffective in increasing grain protein content as split applications either at anthesis or at bothstem elongation and anthesis. These results indicate that maximum spring wheat grain yield, testweight, and protein should be obtained by applying the bulk of seasonal N requirements at plantingand then applying single or double‐split N applications at anthesis on stem elongation and anthesis.