Intensive fertilization (N, P, K, Ca, and S) decreases organic matter decomposition in paddy soil

Paddy soils have experienced intensive fertilization in recent decades. However, our understanding of the effects of fertilization on the carbon (C) cycle remains incomplete. In the present study, we investigated soil organic matter (SOM) decomposition in a 60-day incubation in response to N, P, K, Ca, and S addition to nutrient-limited paddy soil at three low and three high concentrations. High levels of nutrient addition decreased CO2 emission, qCO(2), and microbial biomass. CO2 emissions increased (12-17%) owing to low levels of nutrient addition, whereas it decreased (3-21%) in response to high levels of nutrient addition. Microbial biomass and nutrient turnover rates increased after low levels of nutrient addition. Positive priming effect occurs under nutrient-limited conditions owing to the stimulation of microbial biomass production after low amount of exogenous nutrient input. In contrast, high levels of nutrient addition decreased microbial biomass and net N mineralization. This high N, P, K, Ca, and S addition could satisfy the needs of microbial growth, thereby decreasing the dependency of the organisms on the original nutrients from SOM decomposition. Therefore, negative priming was observed after high-level nutrient addition. In conclusion, intensive fertilization (with N, P, K, Ca, and S) reduces SOM decomposition through increased microbial turnover in paddy soils, which might positively affect C sequestration.