Abstract

The objective of this study was to investigate distribution of phosphorus (P) in different soil profiles as influenced by land-use changes. The study sites were located in six districts of the Maha Sarakham province, Northeast Thailand. Soil samples were collected from five soil depths: 0-20, 20-40, 40-60, 60-80, and 80-100 cm under four adjacent land uses, including forest, cassava, sugarcane, and rice paddy. The air-dried soil samples were subjected to determine available P using a Bray II extractant. The concentration of P was then measured employing a UV-VIS spectrophotometer. When considering P stock at each soil layer, higher P stock was in topsoil (0-20 cm) than in each of the 5 layers of subsoils. Agricultural practices, such as high rate of chemical fertilizer input, can enhance P stocks in soils of upland crops (i.e., sugarcane and cassava), in comparison to paddy and forest soils. Additionally, deep plowing in the upland soils prior to cultivation can induce P leaching from topsoil to subsoil, as seen in the larger amount of P accumulation in the upland subsoil. This study pointed out that the same land use, with different agricultural practices from farmers, could lead to different patterns of P distribution in topsoil and subsoil. To restore P in agricultural soil, fertilizer management for crop cultivation is needed.