NITROGEN MINERALIZATION KINETICS WITH DIFFERENT SOIL PRETREATMENTS AND CROPPING HISTORIES

A laboratory study was conducted to determine how soil pretreatment (air-drying, freezing, and field-moist) and cropping history affects the kinetics of N mineralization. Although most researchers suggest that net N mineralization behaves according to first order kinetics, some have suggested that this process is better described with zero order kinetics. It was hypothesized that the air-drying pretreatment may be largely responsible for an N mineralization pattern which may be described by first order kinetics. Experimental data showed that net N mineralization followed a first order kinetics pattern regardless of pretreatment. However, the air-drying pretreatment enhanced N mineralization during the first 7 d of incubation. The traditionally used first order kinetics model (Model I) was extended to take into account an 'easily' mineralized N fraction (N//e) mostly released during the first 7 d of incubation. This amended model (Model II) generally provided a much better fit to the experimental data, especially for the air-drying pretreatment. As a result of the flush of mineralized N during the first 7 d, the total quantity of N released with air-drying was considerably greater than with the freezing or field-moist pretreatments. Organic N was released in a linear manner over the 42-d incubation period and comprised about 10% of the total N released.