Predicting Water Needs of Wheat from U.S. Class A Pan Evaporimeter at Pantnagar, India *

In field experiments at Pantnagar, India during 1968–70, evapo-transpiration (E T ) in wheat was significantly correlated with U.S.W.B. class A pan evaporation (E 0 ) when the crop was in an active stage of growth and moisture was non-limiting (50 or 25% depletion of available moisture). The estimated E T was higher than E 0 , probably due to ‘oasis’ and ‘clothesline’ effects. When E T measurements were made at varying distances from the upwind side during the subsequent three years, it was found that E T decreased with increasing distance downwind with a conspicuous border effect up to about 25 m distance. In the absence of advective heating, i.e. in extreme downwind locations, the actual E T was 480, 533 and 530 mm during 1970–71, 1971–72 and 1972–73 respectively.