A long-term field trial was carried-out in Jaboticabal (SP) to estimate the effect of production systems on soil nitrogen and soil organic matter fractions. The treatments tested were corn in conventional sowing in summer and no tillage in winter (C-Mi-P), maize in direct sowing in summer and no tillage in winter (D-Mi-P), maize in direct sowing in summer, Mucuna aterrina as green manure in winter (D-Mi-Mu), maize in direct sowing in summer, Cajanus cajan as green manure in winter (D-Mi-Gu), maize in conventional sowing in summer, no tillage in winter and soybean in next summer (C-Mi-P-So), maize in direct sowing in summer, no tillage in winter and soybean in next summer (D-Mi-P-So) and maize in direct sowing in summer, and Crotalaria juncea as green manure in winter (D-Mi-Cr). The experimental design was randomized blocks with four replicates. Following 60 days after plant emergence, soil (0-0.05, 0.05-0.10 and 0.10-0.20 m depth) and plants were sampled. In the soil samples, the following forms of nitrogen were determinated: total-N, nitrate-N, ammonium-N, microbial biomass N, humic matter, fulvic acid, humic acid and humin N. Soil organic matter potential of mineralization was also estimated. N content was evaluated in the maize leaves and green and dried weight determined in the winter crops, which were collected when 50% of the plants were flowering. Nitrogen mineralization potentially higher values were obtained in the 0-0.05 m layer and under direct sowing with or without crop rotation or green manure in the winter. Similar results were obtained for the humic acid N. Conventional sowing with or without crop rotation showed higher mineral N values in the 0.05-0.10 m layer, with higher values for nitrate-N. Conventional sowing increased N mineralization and direct sowing caused a larger input of organic matter and potentially mineralizable nitrogen.
maize; direct sowing; green manure; fulvic acid; humic acid; humin