Evaluation of a predictive model of the effect of temperature and humidity on wheat straw decomposition

Víctor García de Cortázar G.1*, Paola Silva C.1, Edmundo Acevedo H.1

The objectives of this work were to evaluate wheat (Triticum aestivum L.) straw decomposition rates under different temperature and humidity levels in two locations, and to compare the actual measurements with predictions made with the crop growth simulator CropSyst. The decomposition rate was evaluated for three quantities of wheat straw (3; 6; and 9 t ha-1) left on the soil surface and six temperature treatments (defined by the month at which the straw was placed on the field) in two field experiments carried out in Santiago (Metropolitan Region) and El Carmen (VIII Region), Chile. The experimental design was randomized complete blocks in a factorial arrangement with four replicates. In Santiago a third factor was added, irrigation water, with four levels defined by water depth applied via sprinkler. The decomposition rate was measured by the bag method. The same experiments were simulated with CropSyst and the results were compared with the experimental values. Temperature had a significant effect on decomposition rate with increases of more than 200% between extreme temperatures. The water treatments did not produce clear differences, even though there was a tendency to greater decomposition with higher water applications. The comparison of the experimental results with the simulations made with CropSyst, showed over- and under-estimations on the part of the model depending on the date. The differences between the model and field data varied between 0 and 37% with an average of 10%. However, r2 values were over 0.92 and there were no significant differences with respect to an ideal slope of 1.

Keywords: temperature, humidity, modeling, CropSyst, wheat straw.
1 Universidad de Chile, Facultad de Ciencias Agronómicas, Casilla 1004, Santiago, Chile. E-mail: vgarcia@uchile.cl *Autor para correspondencia.