INFLUENCE OF SOLAR RADIATION AND SOIL MOISTURE ON GROWTH AND YIELD OF CHINOOK WHEAT

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Abstract
The influence of solar radiation on the growth and yield of Chinook wheat was determined in a 5-year field shading study, and a 1-year, 3 × 3 shading × soil moisture lysimeter experiment.In the field, shading with saran mesh reduced solar radiation and wind but had little effect on air or soil temperature. In moist years shade maintained soil moisture at a higher level than no shade. Generally, mean leaf area ratio decreased and mean net assimilation rate and relative growth rate increased linearly with increases in the log of light intensity. There were interactions between shading × years (weather) relative to dry matter yield. The efficiency with which solar energy was used for grain production increased with shading. The effect of shading on crude protein and soluble sugars in grain was variable.In the lysimeter shading study, regression equations were used to relate several plant characters to shading and soil moisture (in the available range). Plant height, stem diameter, days to head, number of tillers, weights of grain and of straw, and percent cellulose were negatively related to soil moisture stress; crude protein was positively related. Days to head and crude protein were negatively related to light intensity, but all the other characters were positively related. The partial regression coefficients indicated that the influence of soil moisture stress was much more important than solar radiation on the crude protein content of the grain.