ChileanJAR

This work had as objective to elaborate a simple model of pasture growth, phenology and water balance of annual pastures of Mediterranean climate. The water balance is performerd only in one soil stratum (40 cm), where it is supposed the root mass is concentrated. It was considered rainfall and the water losses by evapotranspiration, which was calculated as a function of the potential evapotranspiration, the relative water supply level of the soil and the degree of pasture cover. The model supposes an adequate contribution of nutrients, being climatic variables, availability of photosynthetic material and soil water the main limiting for the grassland growth. Validation was performed with dry matter accumulation and soil water data measured in Mediterranean grassland at the Hidango Experimental Center, belonging to the Agricultural Research Institute (INIA) (34º06' S lat ; 71º47' W long; 296 m.o.s.l.) during the season 1992. The results of the validation indicated that this model explained over 90% of the variation of the observed values of dry matter accumulation and soil water. Some lines of the model development are proposed, such as the incorporation of subroutines that simulate the nutritive value and the effect of N and shrub stratum, on grassland growth.