Quantification of proton budgets in soils of cropland and adjacent forest in Thailand and Indonesia

Continuous cultivation has the potential to accelerate soil acidification. The influence of cultivation on soil acidification was evaluated by calculating proton budget in a soil-vegetation system including solute leaching, vegetation uptake and organic matter decomposition in cropland and adjacent forest in Thailand and Indonesia. In the forests, excess cation accumulation in wood (2.1-3.8 kmol(c) ha(-1) year(-1)) has contributed to soil acidification at the rate of 0.004 mol(c) for production of 1 mol carbon. In the croplands, soil organic matter loss (2.2-3.9 Mg C ha(-1) year(-1)) has contributed to both proton generation owing to nitrification (1.5-5.0 kmol(c) ha(-1) year(-1)) and proton consumption owing to mineralization of organic anions (3.6-8.8 kmol(c) ha(-1) year(-1)) at the rates of 0.008-0.015 and 0.019-0.026 mol(c) for the loss of 1 mol soil organic carbon, respectively. Although the influence of cultivation on proton budget is different depending on the budget of organic matter and soil types (soil pH and texture), cultivation results in soil organic matter loss and soil alkalinization at least during the initial stage of cultivation in tropical regions.