ZERO VS CONVENTIONAL TILLAGE AND THEIR EFFECTS ON CROP YIELD AND SOIL-MOISTURE

A study comparing zero tillage (ZT) with conventional tillage (CT) crop production in two rotations; fallow-oilseed-wheat, and oilseed-wheat-wheat, was conducted during 1979-1990. In 36 comparisons of ZT with CT over three rotation phases and 12 yr, ZT increased spring soil moisture in nine cases and resulted in no decreases; increased yield in nine cases while decreasing yield in three; and increased moisture use efficiency in six cases with two decreases. Increases in spring soil moisture were not related to precipitation during the non-growing season but may have been influenced by weeds. Increased spring soil moisture with ZT occurred more frequently on fallow than on stubble, presumably because precipitation was greater. Yield increases with ZT generally occurred where spring soil moisture was increased and weeds were adequately controlled. Yield decreases with ZT were normally associated with poor weed control, but in one case poor seed placement with ZT reduced yield. Throughout the study, inadequate weed control with ZT was a major factor limiting responses. Implications of these results on future research required to improve adoption of this important soil-conserving practice are discussed.