STUDIES OF THE EFFECT OF SIMULATED ACID-RAIN ON THE ECOLOGICAL EQUILIBRIUM OF THE SOIL SYSTEM .2. SOIL AS A PHYSICAL-ENVIRONMENT - FLUCTUATIONS OF WATER-RESOURCES IN SOIL DURING THE VEGETATION PERIOD

During the vegetation periods of the years 1988 and 1989, within studi es performed at Dziekanow Lesny near Warsaw, the temporal variation of humidity and water resources in the upper soil layer (loamy sand) was determined. Two experimental plots were observed: one subject to natu ral precipitation and the other watered with natural + simulated preci pitation (8.4 mm weekly). In the vegetation period of a year which had a dry spring and autumn and wet summer (1988), neither of the experim ental plots showed overdrying of the upper 10 cm soil layer. During 96 % of the time, at both experimental plots, water accessible to plants and gravitation water was found. On the other hand, in the vegetation period of a year with a wet spring and autumn and a dry summer, water conditions were different; accessible water and gravitation water occu rred at the experimental plot, alimented with natural precipitation du ring 80% of the time, and at the plot watered with natural + simulated precipitation only during 57% of the time. In the case of rain defici t, small artificial watering in the summer had enhanced evaporation an d decreased the water content in the nearsurface soil layer.