pH,nitrogen mineralization,and KCl-extractable aluminum as affected by initial soil pH and rate of vetch residue application: results from a laboratory study

Purpose

Initial soil pH determines the direction and magnitude of pH change after residue addition. This study aimed to evaluate the relative importance of initial soil pH and rate of residue application in determining subsequent pH change, nitrogen (N) mineralization, and soil-exchangeable aluminum (Al).

Materials and methods

An incubation experiment was conducted for 102 days on a Plinthudult soil and a Paleudalf soil, where pH gradients were produced after application of direct current (DC). Rates of vetch applications were 0, 5, 15, 30, and 50 g kg^?1 soil.

Results and discussion

Increasing rates of vetch application caused greater increases in soil pH, but no consistent increase in soil pH at higher initial pH range (4.40～6.74), because of nitrification. There was a positive correlation between alkalinity production and the initial soil pH at day 14, while correlations became negative at days 56 and 102. Mineral N accumulated as NH₄ ⁺–N in low pH soils, due to limited nitrification, while NO₃ ^?–N dominated in higher pH soils. Application of vetch decreased KCl-extractable Al, probably because of complexation of Al by organic matter and precipitation of Al as a result of increased pH, reductions in Al concentration increased with increasing rates of vetch application. However, this amelioration effect on Al concentration weakened with time in higher pH soils.

Conclusions

Application of vetch residue can significantly increase soil pH and concentrations of mineral N and reduce exchangeable Al. These amelioration effects are enhanced with increased rate of vetch addition and vary with time depending on the initial pH of the soil.