Soil Spatial Variability Effects on Irrigation Efficiency

Higher evapotranspiration rates, reduced rainfall and increased water scarcity have led to a need for improved irrigation water use efficiency. Evaporation is a significant component of the total evapotranspiration (ET) and high evaporation losses reduce the amount of available water for transpiration, resulting in reduced plant water availability and hence increased irrigation. Values for soil evaporation vary widely in the literature, from 27-65% of total ET. In order to increase transpiration relative to evaporation, a reduction in evaporative losses is needed. Spatial variability of evaporation is an important factor that needs to be taken into consideration when improving water use efficiency. Soil physical properties control evaporation by influencing both the transport of water toward the soil or root surface and soil water storage. The effect of variability in soil properties on evaporation is likely to be larger in cases with water deficiency. Cultural practices such as use of narrow row spacing, mulch and minimum tillage can reduce evaporation however, they are not always effective. The potential for major savings of water depends on the length of drying interval following irrigation or rain. There is the potential for reductions in evaporation losses of up to 60% through the use of improved management techniques, enabling more water to be used by the plant for transpiration. In order to improve water use, more research in quantifying evaporation variability at the field scale needs to be completed.