保护性耕作对农田碳、氮效应的影响研究进展

作物产量的高低主要取决于土壤肥力,如何保持并提高土壤肥力是确保我国粮食安全和农业可持续发展的重要任务,也是众多学者关注的焦点。土壤有机碳和氮素是评价土壤质量的重要指标,其动态平衡直接影响土壤肥力和作物产量。随着全球气候变化及环境污染问题的愈加突出,农田土壤固碳及提高氮效率成为各界科学家研究的热点。目前,保护性耕作已成为发展可持续农业的重要技术之一,对土壤固碳及氮素的利用具有很大的影响。深入了解保护性耕作对土壤有机碳固持与氮素利用效率提高的影响机制,对于正确评价土壤肥力有着重要意义。但由于气候、土壤及种植制度等条件不一致,关于保护性耕作对农田碳、氮效应结论不一。阐述了国际上保护性耕作对农田系统土壤有机碳含量变化及其分解排放(如CO₂和CH₄)、氮素变化及其矿化损失(如NH₃挥发、N₂O排放与氮淋失)和碳氮素相互关系(如C/N层化率)影响的研究进展,并分析了其影响因素和相关机理。尽管国内保护性耕作的研究已进行30 多年,但在土壤有机碳与氮素方面与国外相比依然有较大的差距。保护性耕作对土壤固碳与氮素利用的影响机制,碳素和氮素在土壤-植株-大气系统中的转移变化,及结合农事管理等综合评价其生态效应的研究很少。在此基础上,提出未来我国保护性耕作在土壤有机碳固定和氮素利用方面的重点研究方向:(1)在定位试验基础上进一步探讨保护性耕作对土壤有机碳及氮素利用的影响机制;(2)深入研究土壤有机碳和氮素的相互关系及其对土壤肥力的影响;(3)结合环境保护与土壤可持续管理对保护性耕作农田土壤固碳及氮素高效利用的系统评价研究;(4)加强保护性耕作对农田碳、氮效应的宏观研究,合理评价保护性耕措施下对农田碳、氮综合效应。

Advances in effects of conservation tillage on soil organic carbon and nitrogen

Soil fertility is one of the most important factors determining crop production. Maintaining and improving soil fertility, which has become an increasing focus for agricultural scientists, is crucial for food security and sustainable agricultural development in China. Soil organic carbon (SOC) and nitrogen (N) directly affect soil fertility and ultimately crop yield, and thus are considered as important soil quality indicators. With the concerns on global warming and environmental pollution, more attention is being paid on enhancing SOC sequestration and improving N use efficiency (NUE) in cropland. Currently, conservation tillage is widely regarded as an important part of sustainable agriculture and has been adopted by many countries, due to its benefits in conserving soil, saving water, fuel and energy, and protecting the environment. Numerous studies have indicated that conservation tillage (i.e., no-till and minimum tillage) increases SOC and total N storages by reducing soil disturbance and increasing residue retention. Thus, a deep understanding of the mechanisms of conservation tillage on enhancing SOC sequestration and NUE is of fundamental significance for soil fertility assessment. However, there are still controversies about the effects of conservation tillage on SOC sequestration and NUE, mainly due to the diverse climates, soil types, cropping systems, and experimental durations. This paper provides a review about the research progresses of conservation tillage effects on SOC content and decomposition (e.g., CO₂ and CH₄ emission), total N content and mineralization (e.g., NH₃ volatilization, N₂O emission, and NO₃^- leaching), and the relationships between SOC and N processes (e.g., C/N stratification) in farmland systems. Meanwhile, this article also assessed factors and mechanisms that influence SOC and N use. Although studies on conservation tillage have been conducted more than 30 years, there are some gaps between China and the other countries, especially on SOC and N processes under conservation tillage systems. Because of the large differences in experiment conditions, the mechanisms of tillage effects on SOC sequestration and N use are not well understood. Furthermore, systematic studies on carbon and N transformations in the soil-plant-atmosphere-continuum are rare under different tillage systems, which make it difficult to conduct in-depth studies of conservation tillage. Meanwhile, considering the emissions of agricultural practices, few papers have assessed the ecological effects of conservation tillage on the interactions between C and N processes. Therefore, it is necessary to study the underpinning mechanisms that govern tillage effects on SOC sequestration and N use. Our analysis showed that the potential researchable areas and priorities on the influences of conservation tillage on SOC and N processes in China were: (1) strengthen the on-site studies on the mechanisms of conservation tillage effects on SOC sequestration and N use; (2) enhance the study of relationships between SOC and N and their interaction effect on soil fertility under conservation tillage; (3) link environmental protection, sustainable soil management, SOC sequestration and N use; and (4) deepen the study of conservation tillage effects on SOC sequestration and N use in macro-scale.