POTENTIAL AND NET NITROGEN MINERALIZATION IN SOILS

The soil incubation methods can be used as tools to a better evaluation of N mineralization and availability. The objective of this study was to evaluate the potential and net soil organic N mineralization, and relate them to N availability to plants. Twenty two soil samples (0-20 cm) were incubated at 35 degrees C for 30 weeks in aerobic conditions and at 40 degrees C for seven days in anaerobic conditions, and tested in a greenhouse experiment on corn plants. During the 30 weeks-incubation period N mineralization increased in the 2(nd) week, followed by a decrease and stabilization from the 4(th) week afterwards. The mineralized N data was adjusted to an exponential decay model and the accumulated N mineralized (N-mac) data was adjusted to an exponential growth model and the potentially mineralizable N (N-0) was then estimated. The quantities of N-0 expressed N mineralization and availability in the long-term. However, the correlation of N-mac with available N indicated by plants (N concentration and N uptake) was higher than of N-0, and high correlation values were found after two weeks of incubation. This indicates that the statistical adjustment of data may be unnecessary and the incubation period can be reduced. The soil total N was a better indicator of the net and potential N organic mineralization than soil organic matter, especially in the long-term. The incubation for seven days in anaerobic conditions can be used to estimate N-o. The subtraction of initial N-NH4+ from the data obtained after incubation did not improve the estimation of N mineralization and availability by this method, which makes it even more simple and feasible.