Irrigated hard winter wheat response to fall, spring, and late season applied nitrogen.

摘要

High yielding irrigated hard red winter wheat (HRW) is frequently low in protein and marketed at a discount. Protein content is affected by available N but few published reports relate to N fertilization practices for producing high yielding irrigated HRW with an acceptable protein content. In this 3-yr study (1985-1987), effects of fall (autumn) preplant, spring topdress and late N application on yield and protein content of irrigated HRW were investigated. Moreover, flag leaf N concn. (FLN) for scheduling late season N were determined. Early season N treatments for vegetative growth consisted of an untreated control and 168 kg urea N/ha either broadcast preplant and incorporated in the fall, topdressed in early spring or both (336 kg N/ha total). Applying late season N at heading or flowering (0 or 56 kg urea N/ha) was evaluated with all earlier season N treatments. The N applied for vegetative growth increased protein from 15 to 47 g/kg. The timing of N application (fall vs. spring), without late season N, did not affect grain yield but protein was 8-13 g/kg higher with spring topdressed N. Excessive N (336 kg N/ha) during vegetative growth consistently reduced grain yield of non-lodged wheat due to lighter kernels. Protein increases with late season N were highly dependent on the earlier season N rate and timing. Late season N was essential for increasing protein to 120 g/kg without incurring yield losses from excessive N during vegetative growth. FLN was directly related to protein, and inversely related to the late season N induced protein increase. However, the protein relationships to FLN differed markedly among yr. Normalized FLN values, dividing all values for a yr by the highest value in that yr, greatly reduced the yr effects. It is concluded that both high yields and acceptable protein levels in irrigated HRW are possible with sufficient N during vegetative growth for yield and late season N for protein enhancement.