Abstract: Based on long-term field fertilization experiments in subtropical upland and upland-paddy rotation land, the characteristics of long-term accumulation and annual degradation after long-term chemical fertilization (nitrogen, phosphorus, and potassium) combined with crop straw (NPKS) were compared with those of chemical fertilization (NPK). Meanwhile, the main influencing factors on cellulose degradation were clarified from the sights of key enzyme activities, soil properties and climate factors. The results showed that cellulose was not significantly accumulated after long-term (13 years) NPKS fertilization for both lands. After application of NKPS fertilization, the cellulose content was decreased to its initial level after 3 months and 6 months in rotation land and upland respectively, with the faster degradation rate in the former land. After NPKS fertilization, the increment of the activities of cellulolytic enzymes ((cellobiohydrolase (CBH) and β-glucosidase (βG)) were significantly higher in rotation land than in upland, implying a stronger response of cellulolytic enzyme in rotation land to NPKS fertilization. Besides, the proportions of cellulose in soil organic matter (CEL/SOM) were significantly decreased after long-term fertilization in both lands, suggesting that cellulose was not the key component contributing to the accumulation of SOM in subtropical agricultural lands. Correlation analysis and stepwise regression analysis demonstrated that the β-glucosidase, soil microbial biomass carbon and available nitrogen were the key factors determining cellulose degradation. In the future, fertilization and land-use type could be useful strategies to regulate the transformation of soil organic matter and its components in arable lands in red soil hilly region.

Key words: mollisols, long-term fertilization, soil organic carbon, soil particles, enrichment factor.