Effects of Fertilization Regimes on Soil Organic Carbon Fractions and Its Mineralization in Tea Gardens

Changes in the organic carbon fraction and mineralization of soil aggregates play an important role in the improvement of soil quality by organic fertilization. Nevertheless, the effects of organic fertilizer application on the organic carbon fraction and mineralization characteristics of soil aggregates are still unclear. This study carried out a 6-year field trial with five different fertilization treatments, namely, no fertilization (CK), chemical fertilization (CF), rapeseed cake (CR), chicken manure (CM), and a combination of chicken manure with biochar (CMB). The distribution, organic carbon density, and carbon mineralization characteristics in soil aggregate fractions were tested. The results showed that CR significantly increased the contents of large soil macroaggregates and enhanced the stability of soil aggregates of all sizes. CM increased the contents of macroaggregates and microaggregates but decreased the stability of the soil aggregates. CR, CM, and CMB increased the content of soil organic carbon and its components in the tea garden, while the contribution rate of organic carbon to large aggregates was the highest under the CR treatment. Organic fertilizer treatments had a positive effect on enhancing soil microbial biomass and carbon and nitrogen contents. The mineralization rate and accumulation of organic carbon in tea garden soil aggregates were increased under organic fertilizer treatments, of which CMB was the most significant. There was a high increase in tea yield and bud density under the CR treatment. In short, the application of organic fertilizers in tea garden soil is helpful to improve soil nutrients and soil fertility; plant- and animal-derived organic fertilizers are recommended for corporate application in agricultural production.