MODELING THE FLUSH OF NITROGEN MINERALIZATION CAUSED BY DRYING AND REWETTING SOILS

The flush of N mineralization that follows rewetting a dry soil may release significant amounts of N where drying-rewetting cycles are common, so attempts to model N mineralized in the field should include this mechanism. Selecting a model for the N flush, however, is hampered by inadequate measurement frequency in existing data. My objective was to collect detailed data on the progress of the N flush to facilitate finding a model to describe the process. Samples of three soils were preincubated, dried, rewetted, and incubated at 30-degrees-C for up to 20 d with periodic samplings for inorganic N determinations. Undried samples were also incubated and sampled periodically. Cumulative net N mineralized in undried samples was adequately described by zero-order kinetics. In contrast, describing cumulative net N mineralized in dried and rewetted samples required a model with two N pools, one following zero-order kinetics and the other following first-order kinetics. Apparently, the first-order N flush was super-imposed on zero-order background mineralization. Drying and rewetting the soils also significantly increased the background mineralization rate, suggesting transfer of N from a passive pool to the zero-order pool.