Effects Of Crop Cultivation And Intensive Grazing On Organic Carbon Pools And Aggregate Stability In Arid Grassland Soils

Intensive grazing (fenced) is generally recommended a conservative use of grasslands, while cropping is one of major reasons relative to grassland degradation so as to desertification in arid and semi-arid regions. However, their effects on soil organic C pools and soil aggregates stability have not been well understood. This work was designed to investigate the changes in soil organic C dynamics and aggregates stability with relation to cultivation and intensive-grazing (fenced), compared with open-grazing (no-fenced) and therefore we evaluated the sustainability of these two types of grassland uses. The main conclusions as following:1. Compared with open grazing, intensive grazing for 22 years increased soil total organic C, coarse organic carbon and stable organic carbon contents by 20%,16% and 27% respectively, but decreased fine organic content by 19%. Intensive grazing increased soil concentrated-acid extracted carbohydrate C, diluted-acid extracted carbohydrate C, hot-water extracted carbohydrate C and mineralized C (in 51 incubation days ) by 22%,15%, 16% and 30%, respectively, but did not influence microbial C. Compared with open grazing, after 40 years cultivation did not influence total organic carbon, but decreased soil coarse organic carbon and fine organic carbon contents by 29% and 22% respectively, meanwhile, increased stable organic carbon content by 8%. Cultivation decreased concentrated-acid extracted carbohydrate carbon, diluted-acid extracted carbohydrate carbon, hot-water extracted carbohydrate carbon, microbial carbon and mineral carbon contents by 13%,19%,21%,30% and 16% respectively. Our work indicated intensive grazing is advantageous to the soil total organic carbon, the carbohydrate content increase as well as the microorganism activeness enhancement; although cultivation did not causes the grassland soil total organic carbon content significantly declining, the carbohydrate content and microorganism activeness remarkably reduce compared with open grazing.2 Compared with open grazing, intensive grazing has not significantly effect the content of >0.25 mm soil water stable aggregates, but cultivation decreased >0.25 mm soil water stable aggregates content, water stable aggregates ration and mean weight diameter by 74%,77% and 90% respectively. This results show cultivation had the ruinous influence to the grassland soil structure stability in the arid crisscross zones of agriculture and animal husbandry.3 Our research indicated with compared total organic carbon content, carbohydrate carbon concentration were more closed linear relationships to soil water stable aggregates content, stable aggregates ration and mean weight diameter. Between in withdraws in three carbohydrates components, the most linear relationship were found between diluted-acid extracted carbohydrate concentration and soil aggregates stability, It demonstrated diluted-acid extracted...