Studies in the water relations of Pinus sylvestris in plantation conditions. III. A comparison of soil water changes and estimates of total evaporation on four afforested sites and one grass-covered site.
cf. F.A. 26 No. 1678.] Gypsum electrical-resistance blocks were used to follow changes in soil moisture on four forested sites and one grass-covered site for 3 years. The plantations varied from 20 to 32 years in age, and were on soils differing in texture and water-table depth. From the results, total evaporation during the period of soil water deficit was calculated for each site in each year. Available water within the rooting zone was defined as that held between 0.2 and 10 atm. and was estimated from suction measurements. On the forested sites, roots penetrated to about 2 m. and the available water varied from 17 to 37 cm. according to the texture of the soil. The grass roots penetrated to only 60 cm. depth, and available water was only 3.7 cm. Results on the forested sites indicated that the potential evaporation rate was about 1.2 times that of open water (E°). On the only site with a lower evaporation rate than this, the results were consistent with the assumption that the potential rate was maintained until most of the available water was used, and that evaporation then continued at 1/10 of the potential rate. On the grass-covered site evaporation during the months of soil water deficit was about 0.5 E.° and this was consistent with evaporation at the potential rates of 0.8 E° in May-August and 0.7 E° in September, maintained until the available water was exhausted, and then reduced to 1/10. From authors' summary. KEYWORDS: Evaporation in \ plantations \ Forest influences \ evaporation \ Pinus sylvestris water relations \ soil water \ deficit \ Water relations \ plantations