Validation of the soil evaporation subroutine of the SWB-2D model in a hedgerow peach orchard

Abstract

The SWB (Soil Water Balance) model, previously developed to estimate water use by agronomic crops, has been adapted to describe solar radiation interception and soil evaporation in hedgerow orchards. The distribution of solar radiation (Rs) at the soil surface is calculated by the difference between total incoming solar radiation and radiation intercepted by the canopy of the trees. Soil evaporation at different distances from the tree row is calculated as a function of daily potential evaporation, local estimates of Rs, air humidity and humidity of the top soil layer. The soil evaporation routine of SWB-2D was tested using measurements obtained with solarimeter tubes and micro-lysimeters installed across a row in a peach orchard. In an additional experiment to test the lysimeter technique, the micro-lysimeter readings in bare and grass-covered areas in an open field were compared to reference evapotranspiration values calculated by the weather station. Simulated Rs fitted the measurements well, though the dimensions of the tree canopy had to be adjusted to obtain the best fit. Simulated evaporation fitted the micro-lysimeter measurements well in the bare soil area, and the evolution of evaporation patterns during soil drying was reproduced well. In the grass-covered areas, the mulching effect of dormant grass and the continuing transpiration by the active grass should be taken into account in order to accurately simulate soil evaporation.

Keywords:

• Hedgerow
• micro-lysimeter
• peach
• radiant transmittance
• soil evaporation