| Wheat (Triticum aestivum L.) is an important component in the grain crop rotations used in Kentucky farms. The hypotheses tested in this research were: (a) wheat grain protein concentration and yield increase when nitrogen (N) fertilizer rates at both early and late application increase, (b) the grain protein concentration response to N rates depends on timing of N fertilizer application, and (c) wheat grain protein response is related to chlorophyll meter readings, N concentration in flag leaf and culm, soil N levels, and the previous crop. Experiments were conducted for three years (2000-01, 2001-02, and 2002-03), at four locations in western Kentucky. These were laid out in four randomized complete blocks with cultivars as whole plots and subplots as a factorial combination of three early N rates (84, 118, and 151 kg N/ha) applied between Feekes 2 and 5 and three late N rates (0, 22.5, and 45 kg N/ha) applied at Feekes 10. In another experiment, in central Kentucky, the subplots consisted of a factorial application of three late N rates (0, 22.3, and 45 kg N/ha) applied at each of four dates (from Feekes 9 to a week after flowering). Both corn and soybean were represented as preceding crops. In all trials urea was broadcast uniformly, through the crop canopy, to the soil surface. Grain protein in soft wheats increased with increasing N fertilizer rate (from 0 to 45 kg N/ha), applied from Feekes 9 to 10.5. Though grain protein concentration and SPAR readings were positively related, the response of grain protein to late N application was better predicted by the rate of late N than the SPAR meter readings. The average of the several soil N availability indexes measured at each location-year gave the same ranking as soil organic matter in predicting grain protein concentration. However, the level of association was not good enough to use these to predict grain protein response. For each 22.5 kg N/ha, the protein increase averaged about 0.5%. The protein response was relatively insensitive to late N application timing between Feekes 9 and Feekes 10.5 plus 7 days.; Keywords. Nitrogen Fertilization, Wheat Protein, Late Nitrogen Fertilization, Soil Nitrogen Availability, Grain Protein Response. |
