Effect of Land–Use Changes on Nitrogen Distribution in Soil Profile in Northeast Thailand

Abstract

Nitrogen (N) is an important element for crop production. Conversion from forest to agricultural lands can affect soil total N (TN) status in soil. The objective of this study was to investigate amounts of TN in the soil profile as influenced by changes in land use. Soil samples were collected from five soil depths, i.e. 0–20, 20–40, 40–60, 60–80, and 80–100 cm in four adjacent land uses, including forest, cassava, sugarcane and paddy lands located in six locations of Maha Sarakham Province in northeast Thailand. The air–dried soil samples were analyzed for TN using the micro Kjeldahl method. The results showed that TN stocks in topsoil (0–20 cm) in all land uses from six locations were lower than in subsoil (20–100 cm). Total N stock in the whole soil profile (0–100 cm) was highest in Kantharawichai district, but it was lowest in Muang district. Conversion from forest to agricultural lands without appropriate management led to low amounts of TN in agricultural land uses, and the reductions in TN ranged from 5 to 23% compared to the original forest land. However, the same agricultural land use with different management practices led to different amounts of TN stored in soil profiles.