THE EFFECTS OF TILLAGE SYSTEMS AND CROP ROTATIONS ON SOIL CHEMICAL-PROPERTIES OF A BLACK CHERNOZEMIC SOIL

The effects of zero (ZT), minimum (MT) and conventional tillage (CT) systems and three 4-yr crop rotations on soil total C and N, mineralizable N, NO3-N, P, K and SO4-S accumulation and distribution in the soil profile were determined after one 4-yr cycle of crop production on Black Chernozemic Indian Head heavy clay soil. The distributions of available P and K in the profile were not affected by tillage or rotation. Total C and N in the 0-5 cm depth was higher in the reduced tillage systems than in CT, but differences in the 5-10 cm and 10-15 cm depths were not significant. Nitrate concentration was higher in the 15-30 cm and 30-60 cm depths under CT than under reduced tillage. Inclusion of fallow increased accumulation of NO3-N in the deeper soil depths, while inclusion of winter wheat in the rotation reduced deep movement of NO3-N. Nitrate-nitrogen accumulation after field pea production was comparable to that after winter wheat, but a greater proportion of the NO3-N was present near the soil surface after winter wheat, reducing the potential for leaching below the rooting zone. Potential for movement of NO3-N below the rooting zone may be increased by fallow and decreased by production of winter wheat and by reduced tillage systems.