The Effects and Mechanisms of Soil Acidity Changes, following Incorporation of Biochars in Three Soils Differing in Initial pH

In China, it is critical to develop new soil amendments to decrease soil acidity because of the severe soil acidification problems that exist. In the present study, the effects of biochars derived from different feedstocks on soil pH, N transformation, and pH buffering in three acid soils and the mechanisms of changes in these parameters were examined. Soil pH had stabilized by Day 100, and biochar addition increased soil pH by 0.5 to 1 units at the 1% incorporation rate and by 1 to 2 units at 3%, respectively, by 180 d of incubation. The effects of biochar additions on pH changes were determined both by the alkalinity (excess cations) of biochar and N nitrification in soils. With the Psammaquent (loamy, mixed, superactive, thermic Typic Psammaquent) soil, the alkalinity of biochars was the main factor affecting the soil pH increase, while with the Plinthudult (clayey loamy, kaolinitic, thermicTypic Plinthudult) and Paleudalf (clayey loamy, illitic, thermic Typic Paleudalf) soils, both the alkalinity of the biochars and nitrification in the soils contributed to the soil pH changes. In addition, biochar alkalinity made a large contribution to the pH increase while N nitrification made a relatively small contribution to the pH decrease. A positive priming effect of biochar on soil organic N probably occurred during the incubation. Generally, the biochars increased soil pH buffering, and the changes in pH buffering differed between soils and biochars. In conclusion, the incorporation of tested biochars in this study can both increase and maintain soil pH for long periods, and the swine manure biochar had the greatest effect while the reed straw biochar had little effect. The magnitude of the effects depends on soil type, biochar type, and incorporation rate.