Effect of landscape position on the acidification of loess-derived soils under Pinus radiata

Abstract

Interactions between landscape position and the acidifying effect of trees planted into loess-derived grassland soils were studied in the Ventana region of Argentina. Forests of Pinus radiata planted at the end of 1940, were selected in two different positions from the landscape, plains and slopes. Samples of the soil surface mineral horizon were taken from landscape positions at four distances from the trees and compared with grassland soils. The values of the main soil chemical properties changed significantly with distance from trees, with a decrease in pH, base saturation, exchangeable Ca2+, Mg 2+ and K+, and increase in Na+, Al3+ and particularly H+ closer to the trees. This pattern confirms the prominent role of vegetation in bringing about changes in soil properties. Regression models showed high levels of explanation (r2 > 0.85) indicating that a high percentage of the spatial variability of soil chemical properties is systematic and predictable with distance from the trees. The pH in KCl proved an excellent tool for predicting the cationic composition of soils. Organic carbon and total nitrogen were significantly higher in the plains positions than in the slopes under the trees, whereas there was no difference under grassland. The slopes of the regression lines indicated that acidification is more intense in soils on the plains. Vegetation was the main factor influencing acidification of the studied soils. The landscape position regulates the bio-hydrological factor and thus the speed of acidification process.