Comparison of lime- and biochar-mediated pH changes in nitrification and ammonia oxidizers in degraded acid soil

Abstract

Ca-amendments are recommended for soil fertility enhancement in acid soils. Biochar (Bc) can be used as an alternative for the same purpose. Biochar additions have been reported to alter microbial communities in soils and biogeochemical processes including nitrogen (N) cycling. In a microcosm experiment, we investigated the interactive effects of soil pH, the type of soil amendment (lime or biochar), and the NH4 + supply on net N mineralization and nitrification in degraded acid soil and on the abundance of ammonia-oxidizing bacteria (AOB) and archaea (AOA). Soil was incubated under native pH and CaCO3 or biochar-manipulated pH to reach pH 6.2 and 6.8 in the presence or absence of added ammonium for 70 days. Our results showed that Bc had a longer-lasting effect on soil pH than CaCO3, suggesting that Bc could be a preferable liming agent. Increased pH stimulated microbial activity and led to increased N mineralization, which was higher when CaCO3 was applied. Although pH increase and NH4 +-N addition had no immediate effect on nitrification, they synergically enhanced nitrification at the end of the experiment. The amoA gene of AOA consistently outnumbered that of AOB, whereas only AOB amoA gene abundance number was significantly correlated with nitrification and their abundance followed similar trend as NO3 −-N during the incubation. In acid soils where AOB could play a significant role in nitrification, biochar could result in more pronounced changes in N cycle than lime application which could be of especially high interest in intensively managed soils with high N inputs.