Effects of Organic Fertilizer Replacing Chemical Fertilizer on Organic Carbon Mineralization and Active Organic Carbon in Dryland Yellow Soil

Abstract

At present, the effect characteristics and mechanism of organic fertilizer replacing chemical fertilizer on organic carbon mineralization and active organic carbon in dryland yellow soil remain unclear. In order to explore the effect of organic fertilizer replacing chemical fertilizer on organic carbon mineralization and active organic carbon in dryland yellow soil, we used soil with no fertilization (CK), only chemical fertilizer (NP), 50% organic fertilizer replacing chemical fertilizer (1/2(NPM)), and 100% organic fertilizer replacing chemical fertilizer (M). We examined the indoor mineralization culture of organic carbon and explored the characteristics of soil organic carbon and the change in active organic carbon under the condition of organic fertilizer replacing chemical fertilizer. The results showed that organic fertilizer replacing chemical fertilizer increased soil pH, organic carbon (SOC), total nitrogen (TN), and C/N. During the culture period, the soil organic carbon mineralization rate of all treatments decreased sharply in the initial stage (2-4 days), decreased slightly in the middle stage (4-20 days), and tended to be stable in the last stage (20-60 days). After fertilization, the cumulative mineralization of soil organic carbon significantly increased by 7.9%-27.7%. Compared with that in the NP treatment, the cumulative mineralization of soil organic carbon decreased by 5.2% in the 1/2(NPM) treatment and increased by 12.2% in the 1/2(NPM) treatment. Before mineralization culture, the substitution of organic fertilizer for chemical fertilizer had no significant effect on soil recalcitrant organic carbon (ROC) but significantly increased the content of microbial biomass carbon (MBC). The content of dissolved organic carbon (DOC) was significantly increased in the 1/2(NPM) treatment and decreased in the M treatment. After 60 days of culture, the content of soil active organic carbon in all treatments decreased compared with the initial content, of which MBC decreased the most (30.6%-41.2%). The accumulated mineralization of organic carbon was significantly positively correlated with soil pH and SOC and significantly positively correlated with the initial value of MBC and the change value before and after culture. To summarize, 100% organic fertilizer replacing chemical fertilizer significantly promoted soil organic carbon mineralization and reduced soil organic carbon stability; 50% organic fertilizer replacing chemical fertilizer inhibited soil organic carbon mineralization, which was beneficial to soil sequestration and fertilization; and 50% organic fertilizer replacing chemical fertilizer significantly increased soil active organic carbon content, and MBC was used as the main carbon source in the process of soil organic carbon mineralization.