Crop water requirements model tested for crops grown in Greece

A model for estimating: crop water requirements throughout crop development is presented, The model assumes horizontal uniformity and treats the two-c omponent system of canopy and soil along the lines of Shuttleworth and Wall ace (1985). incorporated in the model is a 3-layer soil water budget allowi ng evaluation of the soil surface and canopy resistances and time evolution of the soil moisture in the root zone. Canopy interception is also taken i nto account. Model parameterization considered mostly the crop canopy resistance, assumi ng neutral atmospheric stability conditions, whereas parameterization of th e aerodynamic resistances allows for smooth transition from bare soil to a fully developed crop canopy. The model has been validated with meteorologic al (temperature, relative humidity, wind speed, net radiation flux density, solar radiation flux density and soil heat flux density, precipitation or irrigation) and crop (height, leaf area index and root depth) data collecte d from experimental fields of the Agricultural University of Athens (38 deg rees 23' N, 23 degrees 06' E). Results were verified for three crops (cotto n, wheat and maize) against soil moisture profile changes with very satisfa ctory results. Agreement between observed and estimated evapotranspiration is within 8%. The model is sensitive to crop type and time evolution of the root zone pen etration into soil while precise determination of the minimum stomata resis tance is not exclusively important. (C) 2000 Elsevier Science B.V.,All righ ts reserved.