Critical Stress Periods Affecting Productivity of No‐Till Winter Wheat in Western Canada

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Abstract
The influence of prevailing environmental conditions on wheat (Triticum aestivum L.) yield, grain protein, and yield components is dependent on plant development stage. This study identified critical stress periods influencing the productivity of no‐till winter wheat produced on the Canadian prairies. Grain yield, grain protein, aerial dry matter, harvest index, and individual yield components were related to weather and soil water factors at 11 field locations between 1984 and 1986. Soil types included Typic Haploborolls, Udic Haploborolls, and Vertic Haploborolls. Pan evaporation, precipitation, and growing degree‐days were totalized for six 15‐d periods corresponding with Zadok growth scale stages 21 to 32, 32 to 46, 46 to 65, 65 to 74, 74 to 83, and 83 to 91, respectively. Extractable soil water to 1.3 m was measured at the stem elongation (stage 31), anthesis (stage 65), and soft dough (stage 85) development stages. Environmental stress between stages 21 and 65 most influenced grain yield, aerial dry matter production, harvest index, grain protein yield, spikes per square meter, kernels per spike, and kernels per square meter. Kernel weight was most dependent on prevailing conditions after anthesis. Grain protein concentration was influenced by environmental stresses both before and after anthesis. Evaporation, followed by root zone extractable soil water and precipitation, had the largest influence on crop performance of all the environmental‐water parameters considered. Prediction equations that included these variables explained 91% of grain yield, 82% of aerial dry matter, 84% of the harvest index, 73% of protein concentration, 82% of protein yield, 47% of spikes per square meter, 83% of kernels per spike, 83% of kernels per square meter, and 82% of kernel weight variability observed.