Abstract

Incubation studies were carried out to evaluate the effect of temperature and urea supply level on both the urease activity and the kinetics of N mineralization in two Andisols of Southern Chile. Our results showed that urease activity was higher in Piedras Negras soil (PNS) than Freire soil (FS) at 24 and 48 h, and the enzyme was activated when the temperature increased from 5 to 21 °C. Urease activity followed a simple Michaelis-Menten kinetics. In PNS, the Michaelis Menten constant (K m) decreased, whereas the maximum enzyme reaction velocity (V max) and the catalytic efficiency increased when the temperature was raised up to 21 °C at 24 and 48 h of soil incubation. In FS, urease activity was the highest at 24 h, and it decreased at 48 h as a consequence of substrate depletion. On the other hand, the kinetics of N mineralization data fitted nearly to a single exponential model. At early stages of incubation, similar amounts of mineralized N (N min) were found in both soils. However, N min was 27 to 64 % higher in PNS than FS at the end of the experiment. These results had direct relation with the soil organic matter content, temperature and urea input rates. In PNS, we observed that 47 to 80 % of N min remained as NH + 4 -N, whereas in FS NO3 --N represented between 80 and 96 %. Such differences in the dynamics of N transformation were in accordance with the pH variation registered during the experimental period. These facts have practical implications for agricultural systems management in a particular location, because of the dynamics of N mineralization in Andisols is mainly controlled by the organic matter content and biological properties of soils, as well as by the temperature and urea input rate to the soil-plant system.