EVAPOTRANSPIRATION OF COMMON BEAN AND ITS RELATIONSHIP WITH CLASS A PAN EVAPORATION

Abstract

Rio Grande do Sul state is chara. cterized by climatic variations specially regarding to the amount and distribution of pluviometric precipitation, often occurring some periods of low water availability for spring and summer crops. Studies for the determination of water rclationship with plant-aonosphere system become very important. The purpose of this research was to establish the maximum evapotranspiration of common bean (ETm) and to relate it with Class A Pan evaporation (Eo) to obtain the ratio ETm/Eo (Kc cocfficicnt) at different sub-periods. The field trial was conducted at Centro de Pesquisa de Fruticultura, Fundação Estadual de Pesquisa Agropecuária (FEPAGRO), Taquari, RS/Brazil, 29° 48' South latitude, 51 ° 49' West longitude and 76m of altitude, from 1988 through 1991. The ETm was measured in drainage evapotranspirometers Thomthwaite-Mather type. The total ETm during the cycle (sowing-physiological maturation) changed from 228.2 mm to 361.4 mm along the four years, with an average of 296.4 mm. The sub-period with greater daily mean consumption was that comprised between the beginning of flowering and grain filling stagcs, with an average in the four years of 4.9 mm/day . The mean values for the ratio ETm/Eo at the cycle varied from 0.52 to 0.72, with an average in the four years of 0.60. Kc highest values were observed during the sub-periods: beginning of flowering-beginning of grain filling and beginning of grain filling- physiological maturation.