Evapotranspiration and crop coefficients in white asparagus

Evapotranspiration (ET) and crop coefficients (K-c = ET/ETo) were measured in white asparagus at the Agricultural Research Center of La Rioja (Spain, 42 degrees 27' N, 2 degrees 17' W, 280 m elev.). Crop evapotranspiration was measured daily in a water table lysimeter with asparagus growing in a 200x50 cm arrangement. Daily evaporation E-o was measured in a class "A" evaporation pan and ETo (Kp x E-o) was calculated. Spears were harvested from the end of March until mid June. The ten days average values of ET showed a similar trend in both years increasing rapidly as the ferns developed when the harvest was finished. The seasonal ET values were found between 0.5-4.6 mm/d. ET maximum values achieved 3.6 and 4.5 mm/d in the 4th and 5th years respectively. For the two years mensual averages of Kc were positively correlated with the relative growth of asparagus. Crop coefficients were 0.2-0.3 throughout the harvest period and increased to a 0.4 when the ferns grew up and reached 0.9-1.1 when the ferns were fully developed. Water consumption during the two growing seasons were 274 and 294 mm respectively while lysimeter yields reached 11 and 13.2 t/ha.