[Effects of Chemical Fertilizer and Organic Material Application on Soil Organic Carbon Fractions in Black Soils of Northeast China: A Meta-analysis].

As an important agricultural management practice, fertilization affects the accumulation and stabilization of SOC fractions by influencing the amounts of carbon inputs and outputs. Exploring the effects of different fertilizer types on the SOC content and its main controlling factors could provide a scientific basis for rational fertilization, efficient utilization of organic materials, and SOC content and fertility improvement in the black soil region of Northeast China. This study collected a total of 1 628 observations regarding the effects of chemical fertilizer and organic materials （including organic fertilizer and straw） application on SOC fractions in the black soil region of Northeast China from 228 papers published during 1991 to 2024. A meta-analysis was used to investigate the effects of chemical fertilizer and organic materials application on SOC, dissolved organic carbon （DOC）, particulate organic carbon （POC）, readily oxidizable organic carbon （ROC）, and microbial biomass carbon （MBC） contents. The results showed that： ① The application of chemical fertilizer and organic materials significantly increased the contents of SOC （5%-18%, referring to the range of increase, the same below）, DOC （11%-64%）, POC （30%-141%）, ROC （19%-139%）, and MBC （16%-50%）. The increases in SOC fractions were highest under the manure amendment treatment, with increased SOC content 8% higher than that under straw return and 13% higher than that under the chemical fertilizer treatment. ② The increase in SOC was significantly positively correlated with the fertilizer application duration and the amounts of applied organic fertilizer and significantly negatively correlated with the amounts of straw return, but no correlation was observed with the amounts of applied nitrogen fertilizer. ③ The magnitude of SOC response to fertilization was regulated by annual average temperature and initial soil properties （including pH and SOC）. The fertilization-induced increase in SOC was significantly positively correlated with annual average temperature and initial pH and negatively correlated with initial SOC content. The main factor affecting fertilization-induced SOC changes was initial SOC content under the chemical fertilizer and straw return treatments, while annual average temperature was the key factor under the manure fertilizer treatment. In conclusion, the type and amount of fertilizer, climate conditions, and soil properties should be comprehensively considered to optimize fertilization, so as to increase SOC component fractions as well as improve soil fertility levels in the black soil region of Northeast China.