Relationships between evapotranspiration of corn and the Penman's and Thornthwaite formulas

Abstract

The evapotranspiration (ET) of corn crop (Zea mays L.) (Pioneer X-307 hybrid) calculated during four years (1976-1980) was related in function of the stages, with evaporation calculated by Penman's formula (Eop) and, in monthly basis (November-February period), with the potential evapotranspiration calculated by Thornthwaite formula (ETt). This trial was conducted in Taguari, Rio Grande do Sul, Brazil, 29º 48’15" South latitude and 76 m of altitude. The relation ET/Eop was lower during the early cycle of the crop increased progressively with the development of the plants, and reached maximum values (with mean of 1.10) during tasseling and earing period. After flowering, there was a decrease in the values of the relation until physiological maturation of crop. The relation ET/Eop during the cycle obtained mean value of 0.81. The relation ET/ETt was less during November and February (mean of 0.96 and 0.84, respectively), which coincided with the beginning and the final of the crop cycle and was greater during December and January (mean of 1.34 and 1.28, respectively), which coincided with the flowering and grain filling periods. During the period November-February, the relation ET/ETt obtained mean value of 1.12.