RESPONSE OF WINTER WHEAT TO N AND WATER: GROWTH, WATER USE, YIELD AND GRAIN PROTEIN

Abstract

Nitrogen and water are important variables that influence both grain yield and quality of wheat. The present study was conducted to investigate the combined effects of N and water on the growth, water use, yield and grain protein concentration of stubbled-in winter wheat produced in Saskatchewan. Seven field experiments were conducted between 1984 and 1986 on a range of soil types. Irrigation to approximately 150% of normal growing season precipitation significantly increased grain yield in five of the seven trials. A significant water × N interaction was recorded for grain yield in the remaining two trials. Grain yield response to irrigation averaged 10.9 kg ha−1 mm−1 at total available N levels above 140 kg ha−1. In trials where residual soil NO3–N to 61 cm averaged 40 kg ha−1, 62% of the grain yield increase was due to fertilizer N while 38% of the grain yield increase was due to the interaction between water and fertilizer N. Increases in grain yields due to N and water were attributed to increased levels of pre-anthesis dry matter, a higher number of kernels per square meter and an improved water use efficiency (kg ha−1 grain mm−1 total crop water use). The semidwarf cultivar Norwin and the tall cultivar Norstar responded similarly to N fertilization. In one trial, where moisture conditions were very favorable, a water × cultivar interaction indicated a greater response of Norwin to irrigation. The Gompertz equation was used to describe grain protein concentration-N response. The coefficient that describes the initial lag phase of this function was correlated with dry matter at anthesis (r = 0.97**) and root zone extractable water at stem elongation (r = 0.85**). These observations demonstrate that as pre-anthesis growing conditions improve more N is required to produce an increase in grain protein concentration above a minimum 8.2%.Key words: Wheat (winter), water use, nitrogen