Analyses of the effects of water, nitrogen, and weather on growth, grain yield, biomass production and light use efficiency of winter wheat (Triticum aestivum L.)

Prolonged water and nitrogen stress and weather fluctuations are the major variables affecting crop production. A knowledge of the practical crop limitations are prerequisites to identifying crop performance under different environments. This research investigates the effects of water, and nitrogen stress, and two wheat (Triticum aestivum L.) cultivars on: leaf appearance and the rate of leaf expansion (LE), yield components and the potential translocation of assimilate from the stem to the grain, estimation of leaf area index (LAI), rate of leaf senescence (LS) and light use efficiency by using spectral measurements. Field experiments were conducted in 1986 and 1987 at the Evapotranspiration Research site of Kansas State University. The experimental design consisted of twenty-four treatments combinations which were replicated four times in a split-split plot design.; Leaf appearance was governed by temperature. Nitrogen limited the LE and the final leaf size. Grain yield per unit area was affected by water and nitrogen stress, and weather conditions. Number of ears and grains/m{dollar}sp2{dollar}, and kernel weight were the most important yield components. The losses of stem weight were affected by nitrogen and water.; Changes caused by water, nitrogen, and cultivars on LAI were manifested on reflectance measurements. Normalized difference (ND) and near infrared to red ratio (NIR/R) were used to estimate LAI. ND was more useful to predict LAI than NIR/R. The rate of LS may be predicted by the NIR/R slope.; Differences in dry matter (DM) accumulation due to water, nitrogen and cultivars were associated with the intercepted photosynthetic active radiation (PAR) and LUE (g/MJ PAR). High LUE values were associated with high water, nitrogen levels, and the cultivar Colt. LUE may not be stable because significant differences in LUE were found between double ridge to terminal spikelet and from terminal spikelet to anthesis. LUE was similar for 1985 and 1986 but different from 1987 (drier and warmer year).