The understanding of the effects of the environmental variables on crop growth is very important in order to give the agronomists and the farmers some inputs about crop performance and so about crop yield for a given climate conditions. Several simulation models, simple and complex ones, have been developed during the last years to estimate crop growth and yield. Those models have been proved to be a very important research tool in agriculture. However, as a general, these models require many parameters and therefore are very difficult to make a day-to-day use of such models in some countries. In this paper a simple model to describe and summarizing crop growth, the Expolinear model (Goudriaan and Monteith,1990), was tested for soybean crop growing under tropical (Brazil) and temperate (Argentina) conditions. This model is a simple description of crop growth with a very sound physiological background. However, the sensitive of this model and its assumptions to different environmental conditions are still to be tested.
A determinate and an indeterminate variety of Soybeans were grown under irrigation in the experimental area of the Faculdad de agronomia de Azul (Argentina) and of the Universidade Federal de Viçosa (Brazil). Measurements of leaf area and crop dry weight, including roots, were taken at two days interval in the first month and at seven day-intervals afterward. Meteorological data were collect by an automatic weather station near the experimental fields. The data from emergence until crop maturity were fitted using The Expolinear model. The results have shown that this model was able to summarize and to estimate crop growth in both countries and therefore had shown a great potential to be used to predict crop growth. Also, the results were able to explain differences in Maximum absolute crop Growth Rate, Maximum Potential relative crop growth rate and the timing parameter (lost time) found in the two experiments.