Evapotranspiration and Water-Use Efficiency of Alfalfa in the Subtropical Region of Brazil

Alfalfa (Medicago sativa L. cv. Crioula) is a high quality forage crop grown in southern Brazil as a dryland hay crop. Rainfall is usually sufficient for economic but not maximum yield. Accurate daily and seasonal evapotranspiration data needed for alfalfa irrigation scheduling have not been reported for this subtropical region of Brazil. Daily alfalfa maximum evapotranspiration (BTm) was measured with a mechanical weighting lysimeter installed in the centre of a 90 m by 60 m plot and Eldorado do Sul, Brazil (30"0S'S; 51°39'W; altitude 46 m asl), from October 1989 through September 1990, for 7 harvests. The BTm mean ranged from 1.7 to 7.1 mm/day. The alfalfa water•use efficiency (WUB), defined as the ratio of above• ground dry matter (DM) accumulation per area to evapotranspiration, was also investigated. The WUE ranged from 3.71 to 9.59 kg DM/ha/ mm.