AGROCLIMATIC ANALYSIS OF WATER AVAILABILITY FOR COMMON BEAN IN PLANALTO MEDIO OF RIO GRANDE DO SUL STATE, BRAZIL

Abstract

The objective of this work was evaluate the water soil availability for com mon bean (Phaseolus yulgarisL.) crops in the region of Planalto Médio —Rio Grande do Sul, Brazil, in different sowing times, during the period 1975 —2002, considering different values of water availability in the soil. Crop water requirements were determined at different periods, using crop coefficients obtained from the relation between the maximum crop evapotranspiration (ETm) and the reference evapotranspiration estimated by penman's formula. The average values of total evapotranspiration in the entire crop cycle ranged from 337 mm, for crops sown in November in Cruz Alta to 384 mm for crops sown in September and November, in Julio de Casti lhos. The highest averaged values of evapotranspiration were obtained at Julio de Castilhos, followed Passo Fundo and Cruz Alta. Frequent water deficits were detected in the three local it ies, with mean total values in the entire cycle rangi ng from 38mm to 97mm. The highest mean values of water deficiency were verified in Julio de Castilhos for the water availability in the soil of 50mm, and the lowest values occurred in Passo Fundo for a soil water availability of 70mm, with intermediary values in Cruz Alta. For the three places the highest estimated water deficits correspond to the sowing date of October, from the beginning of flowering to the beginning of grain filling stages as wel I as from the beginning of grain filling to the physiological maturity. The lower ri sk to grain production was obtained in sowing date of September.