COMPARISON OF ENERGY AVAILABLE FOR EVAPOTRANSPIRATION UNDER IN-FIELD RAINWATER HARVESTING WITH WIDE AND NARROW RUNOFF STRIPS

The aim of the study was to quantify the energy balance components and to estimate evapotranspiration (ET) from maize crops under in-field rainwater harvesting with wide and narrow runoff strip length (RSL) treatments. Based on micrometeorological measurements, energy balance components were compared for selected days under dry and wet conditions. Diurnal changes and daily evaporation flux peaks around midday were analysed. The average fraction of available energy was used to evaluate the efficiency of converting available energy to latent heat flux (LE). The results indicated that LE was higher in wide compared to narrow RSL during dry and wet conditions. However, sensible heat showed lower values on wide RSL during wet conditions due to the advective effect of the runoff area. The wide RSL with a higher basin leaf area ratio (BLAR) of 2.43 had more ET and used more energy on evaporating water compared to narrow runoff with a lower BLAR of 1.42. Wide runoff strips converted the higher available energy more efficiently into a higher biomass production than the narrow RSL. During wet days, the wide RSL used more than 70% of the available energy, while the narrow RSL response to the available energy (63%) was stronger during dry compared to wet days. Copyright (C) 2012 John Wiley & Sons, Ltd.