牲畜排泄物返还对草地土壤氮转化和氧化亚氮(N2O)排放的影响研究进展

牲畜排泄物返还被认为是对草地的一种天然的施肥措施,也是草地养分归还的一种重要途径,对于维持土壤肥力和植被生产力具有十分重要的生态学意义。论述了放牧牲畜粪便和尿液自身降解及其氮素变化、粪尿返还对草地土壤氮转化和氧化亚氮(N₂O)排放的作用机制及影响效应,指出排泄物氮输入使粪尿斑块成为草地土壤氮转化和N₂O排放的活跃点,且不同排泄物类型、土壤理化特性和气候条件等使土壤氮素矿化、固持、硝化及反硝化等关键过程具有复杂性和差异性,进而导致不同类型草地生态系统N₂O排放对牲畜排泄物返还的响应不尽相同。建议未来在全球气候变化背景下,应加强草地牲畜排泄物-植被-土壤体系氮素生物地球化学循环过程的系统研究,进一步加深天然草地关键氮素转化过程和N₂O排放的微生物作用机制方面的认识,从而有助于为优化放牧牲畜排泄物的管理模式、制定科学合理的草地土壤养分调控策略和维持草地生态系统可持续发展提供科学有效的理论指导。

Research progress on livestock excreta returning on soil nitrogen transformation and nitrous oxide emission in grasslands

Livestock excreta deposition is considered as a natural fertilization measure in grassland and also an important pathway for the return of grassland nutrients, which may generate greatly ecological significance for the maintenance of soil fertility and vegetation productivity. In this study, we systematically elaborated the variation of nitrogen embedded within grazing livestock dung and urine patches during its natural decomposition, so as to investigate the possible functional mechanisms and influential effects of livestock dung and urine application on soil nitrogen transformation process and nitrous oxide (N₂O) emission. Results showed that livestock excreta nitrogen input made the grassland area covered by dung and urine to become an active point for soil nitrogen transformation and N₂O emission. Generally speaking, the degradation rate of livestock dung was slow and its nitrogen release usually lasts for a long time, which may generate a series of effects on the soil nitrogen transformation and N₂O emission in the natural grassland. On the contrary, livestock urine deposition would rapidly increase soil mineralized nitrogen content in a short period of time, thus may generate a certain of priming effect on nitrogen dynamic and its form transformation in soil profiles, which probably deeply change the soil available nitrogen contents and the microenvironment that related to N₂O emission. It is worth noting that the differences in dung and urine patch shape, physicochemical properties, degradation and nitrogen release characteristics would inevitably alter the soil redox condition, nitrogen content and its form features of grassland soil profiles in different degrees, which may cause the complicated temporal-spatial response of soil nitrogen migration and transformation processes and the microbial functional mechanism differences in N₂O generation and emission. In addition, the differences in excreta types, soil physicochemical properties, and climatic conditions would complicatedly influence the major processes of soil nitrogen mineralization, immobilization, nitrification and denitrification, and therefore resulted in differential response of N₂O emission in different grassland ecosystems. Scientific suggestions were put forward that more attentions should be paid to strengthening the systematic research on the nitrogen biogeochemical cycling in the faecal-vegetation-soil system of grassland under the background of climate change, in order to deeply improve the theoretical understanding of major nitrogen transformation process and microbial mechanism of N₂O production and emission in the natural grassland. The results would provide scientific and theoretical guidance for optimizing livestock excreta management models, and formulating reasonable regulation strategies of grassland soil nutrients, so as to maintain the sustainable development of grassland ecosystems.