SOIL ORGANIC-MATTER CHANGES AND CROP RESPONSES TO FERTILIZER UNDER CONSERVATION CROPPING SYSTEMS IN THE SEMIARID TROPICS OF NORTH QUEENSLAND, AUSTRALIA

Soil organic matter changes due to cropping in the semi-arid tropics were studied in an area with cropping potential. Soil organic carbon and total nitrogen (N) decreased after clearing and tillage, but the decline was less where pasture-crop rotations were used. Crop N removal was high and exceeded the recommended fertiliser N rate. These results suggest that if cropping expansion occurs, careful management is necessary for long-term productivity and land resource protection.