Quantification of Anthropogenic Acidification Under Long-term Fertilization in the Upland Red Soil of South China

Soil acidification in croplands is largely affected by various fertilization practices in long-term scales. However, the differences from the sources and sinks of proton in agroecosystems between long-term fertilization practices are poorly understood. Based on the role of the carbon and nitrogen cycle in soil acidification, experimental data from 1991 to 2006 involving wheat (Triticum aestivum) and maize (Zea mays) rotation in the upland red soil of south Chinawas used to advance the methodology for quantifying soil acidification in croplands. One no-fertilizer control and seven fertilization treatments with 300 kg ha(-1) year(-1) nitrogen were analyzed in the study. Soil net acid addition rates (NAAR) in the long-term scale were significantly and positively correlated (P < 0.01, n = 8), with rates of decline in topsoil pH varying from 0.006 to 0.122 units year(-1). Total proton sources with similar values (17.73-19.53 Kmol ha(-1) year(-1)) and the negative and linear correlation between the effects of nitrogen cycle (H-NCE) and carbon cycle (H-CCE) were found under all fertilization treatments. Characterized as the distribution of a larger percentage in H-CCE than in H-NCE, mineral fertilizer amendments with manure at the appropriate nitrogen rate should be regarded as the optimal nutrient-management strategy for sustainable agriculture in the upland red soil.