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

Two field experiments were carried out in a semiaridregion 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 wereplanted on Jan 4 (San Adolfo) and Nov 27 (Nueva Roma) in 0.75m wide rows and at 400000 pl/ha during two consecutive growingseasons. Energy balance and evapotranspiration (ET) were estimatedduring the reproductive stages from full bloom (R2) to fullmaturity (R8). In Nueva Roma ET or latent heat flux (LE) was estimatedusing the Bowen ratio-energy balance (BREB) (LEb) and thePriestley-Taylor equation (LEPT) with αPT=1.26, 48 h after irrigationor rain. Both methods could be used to predict ET since the ratioLEb/LEPT ranged between 0.83 and 0.95. The observed Bowen ratiovalues were almost 0 during and after rain and increased to approximately0.45 several days after rain. In San Adolfo LE was estimatingusing the Priestley-Taylor equation. For both sites the regressionanalysis for comparison available energy (Rn-G) and LE usingBREB or LEPT indicated that, approximately 90% of the availableenergy was consumed by LE without detecting significative advectiveconditions.