EFFECTS OF VARIOUS QUANTITIES OF STRAW MULCH ON THE GROWTH AND YIELD OF SPRING AND WINTER WHEAT

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Abstract
The effects of applying a wheat straw mulch at various rates to a trash-free summerfallow field immediately after seeding spring and winter wheat were studied for 9 years. Rates of 4000 and 5000 lb or more per acre significantly depressed mean yields of spring and winter wheat, respectively. Straw at rates of 4000 to 5000 lb completely shaded the soil surface when spread uniformly. Higher rates delayed maturity up to 4 to 6 days, shortened height of plants, occasionally lowered nitrate production, and had a negligible effect on plant population and percentage protein of the grain. Each 1000-lb increment of bright straw depressed the late-morning temperature in the 4- to 8-in. depth of soil by an average value of 0.51° F during the early growth period. The depression increased with the season to a value of 0.65° F by mid-June and then decreased to a value of 0.25° F by mid-July, when the crop, in the headed-out stage, almost completely shaded the soil surface.A quantity of mulch up to 4000 lb per acre can be used without deleterious effects on the crop. Quantities of 4000 lb or more should be managed so that the soil temperature depression associated with complete shading of the soil is avoided.