A SIMPLE MODEL TO PREDICT N MINERALISATION OF GREENHOUSE SOILS

Abstract

The formulation of a correct N fertilisation advice, besides a measurement of N-min at the start of the growing period, mainly depends on the possibility to predict the N mineralisation out of soil organic matter. This study aimed to model the N mineralisation of greenhouse soils, using both easily available and easily measurable parameters. Two laboratory incubation experiments were set up. The first incubation experiment allowed to deduct a zero-order model, N-t = kt, in which N-t = N mineralised [kg N ha(-1)], k = N mineralisation rate constant [kg N ha(-1) day(-1)] and t = time [days], whereas the temperature dependence of the N mineralisation rate constant was deduced out of the second incubation experiment. The N mineralisation rate constant further depends on the N mineralisation potential of the soil and on the 'soil's age', i.e. being the time the soil has been glass-covered, eventually leading to the following simple N mineralisation model: N-t = (-9.965 + 0.104 N-KCl + 0.336 T + 0.095 O)t, with N-KCl = N-min in a hot KCl-extract (100degreesC) [kg N ha(-1)], T = temperature [degreesC] and O = soil's age [years]. Though the via the model calculated (k(mod)) and experimentally obtained (k(exp)) N mineralisation rate constants were closely related and a linear relationship was found k(mod) = 0.872 k(exp) (R-2 = 0.719, alpha<0.01), further research is necessary to evaluate this model in-situ. In the long run it will be incorporated into a nitrogen fertilisation advice system for greenhouse crops.