Actividades enzimaticas y contribucion de residuos de cosecha de maiz al nitrogeno del suelo en sistemas de labranza, en Ilanos centrales, Venezuela

The nutrient release from organic residues depends on the chemical and physical properties, as well as the environmental conditions and microbial population in the soil system. The objectives of the present study were to determine the enzymatic activities related to N mineralization, and to estimate the contribution of crop residues on soil N under different tillage practices using corn residues in the Central Plains, Venezuela. In a field experiment, corn residues labelled with 15N were incorporated in soil to evaluate three tillage practices: Direct planting (SD), direct planting after a chisel pass (CSD), and conventional tillage (LC). The amount of N released from crop residues and the deltaN were larger with the LC treatment than with SD and CSD treatments. Enzymatic activity was concentrated in the topsoil layer (0 to 10 cm), and there were significant differences between the two enzymes (protease and urease) in soil at 10 to 20 cm deep, where LC treatment had more enzymatic activity. These results suggest that the application of crop residues with low lignin:N and C:N ratios in a soil with a low C:N ratio, the decomposition rate of crop residues will be faster, probably because of the increase in biological activity of the soil (larger proliferation of urealytic and proteolytic organisms), which could have shown up through an increase in soil N with N released from crop residues.