MODELING THE INFLUENCE OF MOISTURE AND TEMPERATURE ON NET NITROGEN MINERALIZATION IN A FORESTED SANDY SOIL

Soil from beneath an 11-year-old P. radiata plantation was incubated under a factorial combination of temperature (5, 10, 15, 20 or 25-degrees-C) and moisture (10, 20, 40, 60, 80 or 100% of field capacity; 0.26 g g-1) for 15, 30 or 60 days. Mineral N production was a linear function of time for the majority of treatments and could be represented by zero-order kinetics. The influence of soil temperature or moisture on net N mineralization could be explained using simple exponential and logistic functions which respectively explained 98 and 91% of the variation in mineralization. These simple functions were combined in a simple linear model which accounted for 95% of the variation in in vitro mineralization. The model was used, in conjunction with field measurements of soil moisture and temperature, to predict in situ net N mineralization on four consecutive periods between October 1992 and May 1993. Good agreement was obtained between modelled and measured in situ mineralization for three of the four periods. The model was used to examine the effect of constant cf. varying soil moisture content on estimated in situ mineralization. The results suggest that in situ procedures which maintain soil at a constant moisture content may fail to approximate true rates where moisture contents are subject to temporal variation.