IMPACTS OF DIRECT-SOWING MULCH-BASED CROP SYSTEMS (DMC) ON WATER, MINERAL NITROGEN AND SOIL CARBON DYNAMICS IN THE BRAZILIAN CERRADOS

Abstract

Under the humid tropical climate of the Brazilian Cerrados, there is a need for new cropping systems in order to sustain agricultural production. Direct seeding mulch-based cropping systems (DMC) with the introduction of a cover crop before or just after the commercial crop have been developed. By adopting DMC systems farmers are able to make more efficient use of the natural resources and to increase annual total biomass production. Crop residues protect the soil throughout the year and increase the organic matter input to the soil. Since 1999, several studies in a Franco-Brazilian collaborative project have aimed to quantify DMC impacts, on water, carbon and nitrogen dynamics. DMC systems decrease significantly water surface runoff, thereby decreasing soil erosion losses. Cover crops in DMC systems are also able to recycle part of the excess water after harvest of the commercial crop. Because of more favourable conditions under DMC compared to conventional systems, soil organic matter mineralisation is increased during the growing season. Additionally, part of the soil protecting organic mulch mineralizes at the same time. Consequently, under DMC the commercial crop benefits from a larger supply of inorganic nitrogen. The cover crop is also able to recycle part of the mineral nitrogen that was non used by the commercial crop, and nitrogen mineralized after harvest of the commercial cycle. Under DMC the more intense microbial activity is also responsible for higher CO2 emissions to the atmosphere compared to conventional cropping systems. Nevertheless, the net soil carbon balance is positive for DMC systems, principally because of the large crop biomass production and organic inputs due to the introduction. of cover crop As a result under the humid and hot conditions of the Cerrados, the soil carbon content increases under DMC.