WATER-BALANCE AND SOIL-MOISTURE DYNAMICS OF FIELD PLOTS WITH BARLEY AND GRASS LEY

A physically based soilwater and heat model was used to estimate the water balance of an arable field in central Sweden for each of three different crop covers (barley with and without N fertilization and grass ley). Annual water balances were calculated for each year from 1981 to 1985. On-site measurements of soil physical properties, meteorological variables and plant development were used as input to the model. Simulated soil frost, snow cover, soilwater contents, soilwater tensions and relative differences in simulated drainage between treatments were in agreement with the corresponding measured values. In the simulation, surface runoff (70 mm year-1 in all treatments) mainly occurred during snowmelt periods and accounted for much of the variation in the total runoff estimate. Annual mean precipitation amounted to 610 mm year-1, whereas average evapotranspiration was calculated to be 320, 360 and 435 mm year-1 in barley without N fertilization, barley with N fertilization and grass ley, respectively. Soil evaporation accounted for 60, 43 and 23% whereas evaporation of intercepted water accounted for 5, 12 and 19% of the total evapotranspiration, respectively. Drainage estimates amounted to 205, 170 and 110 mm year-1.