VEGETATION EFFECTS ON SOIL SOLUTION COMPOSITION AND EVAPOTRANSPIRATION - POTENTIAL IMPACTS OF SET-ASIDE POLICIES

As an increasing amount of European arable land is being set-aside, th e impact of non-agricultural vegetation types on freshwater and ground water formation becomes increasingly important. Terrestrial ecosystems are widely recognized to be a major factor in determining the quality of groundwater and streamwater. However, to a certain degree, the veg etation will also affect the quantity of water delivered to groundwate r and streams. In this study, the differences in composition of soil s olution and water-use between arable, grassland and heathland sandy so ils were investigated over 2-4 years, with particular reference to the changes occurring as arable soil is set aside as low productive grass land. The arable soil had consistently higher amounts of nitrate, phos phate, potassium and calcium in soil solution, and even though the ara ble soil was planted with winter barley or winter rye, nitrate concent rations at a depth of 90 cm during winter, reached levels above 2 mM. When arable soil was planted as 'set-aside' grassland, the soil soluti on almost immediately converged to the level of heathland sites with r egard to nitrate. Notably, the grassland sites were lower in chloride, sodium and in one region also phosphate concentrations, than the corr esponding heathland sites, presumably owing to the accumulation of bio mass and litter. In order to simulate the water content in the rootzon es of the heathland and grassland soils, it was necessary to decrease the vegetation-specific potential evapotranspiration to 40-60% of that required to simulate the water content of the arable plot. This could indicate that the delivery of freshwater was greater from the grassla nd plot than from the adjacent arable plot. In conclusion, the amount of inorganic constituents in the soil solution from low yielding grass land soils was comparable with that from heathland, while the evapotra nspiration from the grassland soil was considerably lower than that on an adjacent arable soil. Thus, by choice of vegetation and management strategy, it is possible to gain some control of the quantity as well as the quality of water delivered from set-aside soil.