Chengliang Li;Jiangbing Xu;Yuan-Qiu He;Yanli Liu;Jianbo Fa

College of Resources and Environment, Shandong Agricultural University, Tai'an 271018 (China); National Engineering Laboratory for Efficient Utilization of Soil and Fertilizer Resources, Tai'an 271018 (China);Institute of Soil Science, Chinese Academy of Sciences, Nanjing 210008 (China);Institute of Soil Science, Chinese Academy of Sciences, Nanjing 210008 (China

basoc;aggregate stability;npk;incubation;fertilized soil;fertilize

Biologically active soil organic carbon (BASOC) is an important fraction of soil organic carbon (SOC), but our understanding of the correlation between BASOC and soil aggregate stability is limited. At an ecological experimental station (28 degrees 04'-28 degrees 37' N, 116 41'-117 degrees 09' E) in Yujiang County, Jiangxi Province, China, we analyzed the dynamic relationship between soil aggregate stability and BASOC content over time in the red soil (Udic Ferrosols) fertilized with a nitrogen-phosphorus-potassium chemical fertilizer (NPK) without manure or with NPK plus livestock manure or green manure. The dynamics of BASOC was evaluated using CO2 efflux, and soil aggregates were separated according to size using a wet-sieving technique. The soils fertilized with NPK plus livestock manure had a significantly higher content of BASOC and an improved aggregate stability compared to the soils fertilized with NPK plus green manure or NPK alone. The BASOC contents in all fertilized soils decreased over time. The contents of large aggregates (800-2000 pm) dramatically decreased over the first 7 d of incubation, but the contents of small aggregates (< 800 mu m) either remained the same or increased, depending on the incubation time and specific aggregate sizes. The aggregate stability did not differ significantly at the beginning and end of incubation, but the lowest stability in all fertilized soils occurred in the middle of the incubation, which implied that the soils had a strong resilience for aggregate stability. The change in BASOC content was only correlated with aggregate stability during the first 27 d of incubation.