GROWTH AND NPK UPTAKE BY SOYBEAN CULTIVARS IN NORTHERN U.S.A. UNDER REDUCED TILLAGE SYSTEMS

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Abstract
A field study was conducted during 1985–1987 on a Fargo clay soil to evaluate growth, and NPK content at beginning flowering, pod fill, and mature seed at harvest of an early- (McCall) and a late-maturity (Dawson) soybean (Glycine max (L.) Merr.) cultivar as influenced by conventional (plow) or reduced (sweep, intertill, no-till) tillage systems and weed control methods. Excellent seed emergence was obtained on all tillage systems. Fall application of granular herbicide provided excellent weed control but herbicide plus cultivation caused reduced plant growth. Tillage system did not significantly affect plant and seed dry matter production. Yearly differences in dry matter production between early- and late-maturity cultivars depended on precipitation distribution. N and P uptake at pod fill was equal to seed uptake while K in the seed was one-half that measured at pod fill. Stratification of P and K in the surface soil profile of the reduced tillage systems was not detrimental and possibly enhanced early growth when root development was not extensive. Plants exhibited chlorosis on only the plow system under wet soil conditions indicating improved internal drainage under the reduced tillage systems. Interactions of climate with tillage system and cultivar maturity were more pronounced in this soybean study than previously reported which may be related to the cool, dry northern area.Key words: Soybean, no-till, zero-till, weed control, plant nutrients, cultivars, soil nutrient stratification