Studies in the water relations of Pinus sylvestris in plantation conditions. 2. The annual cycle of soil moisture change and derived estimates of evaporation.
In continued work [cf. F.A. 25 No. 54], tensiometers and electrical resistance blocks were used to measure water tension and, indirectly, water content, under the plantation over 6 years. The soil dried to a depth of ca. 2 m. and soil water deficits of 12-32 cm. accumulated in summer. Water tensions in the rooting zone rarely rose above 2 atm. and even in 1959 exceeded 5 atm. only in a limited part of the zone. The soil round the tree bases appeared to be dried more rapidly in summer and wetted more rapidly in winter. Tensiometer readings were interpreted to indicate the times when profile drainage ended in spring and was resumed in winter (assuming that in the intervening period evaporation equalled precipitation). Ratios of these estimates to Penman's estimate of evaporation from an open water surface ranged from 0.98 to 1.20, with a mean for the 6 years of 1.10. Allowing for capillary rise, the mean may be increased by not less than10. From author's summary. KEYWORDS: Catchment areas hydrological research \ whole catchments \ Evaporation in \ plantations \ Forest influences \ soil moisture regime \ Forest influences \ stream flow \ Hydrology \ Pinus sylvestris water relations hydrological \ soil water \ seasonal variation \ Water conservation