Mass transfer from discrete water drops on leaves in a cereal canopy

The boundary-layer resistance, r _d , for water vapour transfer from single drops on a wheat leaf was derived from field measurements of the evaporation rate, drop temperature and air humidity. Parameters are estimated in an equation to calculate r _d from drop diameter and wind speed. The relationship between resistance and wind speed is compared with that from other sources, and possible systematic errors in temperature measurements are examined using a model of the drop energy balance.On secondment from Department of Agricultural Sciences, University of Bristol, IACR, Long Ashton Research Station, Long Ashton, Bristol BS18 9AF, U.K.