[Effects of fertilization and water addition on soil acid neutralizing capacity in an old-field grassland]

Increasing nitrogen (N) deposition results in soil acidification in grasslands. Acid buffering capacity of soil is a critical index evaluating soil acidification, the response of which to N input is regulated by precipitation and concentration of other limiting elements. To explore the responses of soil acidification to N, phosphorus (P), and water inputs, we conducted a 13-year field experiment in an old-field grassland and calculated the acid buffering capacity (ABC) and acid neutralizing capacity (ANC) at the reference of pH=5.0 (ANC_pH5.0) and 4.0 (ANC_pH4.0), using quadratic curve fitting model. The results showed that, without water addition, single N addition or combined with P addition significantly decreased soil pH, ANC_pH5.0 and ANC_pH4.0, whereas single P addition had no significant effect on soil pH, ANC_pH5.0 or ANC_pH4.0. With water addition, the addition of N or combined with P decreased soil pH, ANC_pH5.0 and ANC_pH4.0, whereas P addition decreased soil pH, increased ANC_pH4.0, without effect on ANC_pH5.0. In contrast with treatments without water addition, water addition had positive effects on soil pH, ANC_pH5.0 and ANC_pH4.0. For soils with different initial soil pH values, it was better to select ANC rather than ABC as an index to evaluate soil anti-acidification capacity.