Evapotranspiration and energy balance measurements over a soybean field in the semiarid sowthwestern region of Buenos Aires province (Argentina)

Abstract

Two field experiments were carried out in a semiarid region of Argentina over a soybean (Glycine max L. Merrill) field. The sites of study were San Adolfo (39˚ 23’ S, 62˚ 22’ W, 22 m.a.s.l.) and Nueva Roma (38˚ 29’ S, 62˚ 39’ W, 70 m.a.s.l.). Soybeans were planted on Jan 4 (San Adolfo) and Nov 27 (Nueva Roma) in 0.75 m wide rows and at 400000 pl/ha during two consecutive growing seasons. Energy balance and evapotranspiration (ET) were estimated during the reproductive stages from full bloom (R2) to full maturity (R8). In Nueva Roma ET or latent heat flux (LE) was estimated using the Bowen ratio-energy balance (BREB) (LEβ) and the Priestley-Taylor equation (LE_PT) with α_PT =1.26, 48 h after irrigationor rain. Both methods could be used to predict ET since the ratio LEβ/LE_PT ranged between 0.83 and 0.95. The observed Bowen ratio values were almost 0 during and after rain and increased to approximately 0.45 several days after rain. In San Adolfo LE was estimating using the Priestley-Taylor equation. For both sites the regression analysis for comparison available energy (Rn-G) and LE using BREB or LE_PT indicated that, approximately 90% of the available energy was consumed by LE without detecting significative advective conditions.