长期不同施肥模式下砂姜黑土有机质平衡点差异的形成原因及机制研究

Fertilization is beneficial to improving soil fertility. However, soil organic matter would reach a stable level after a long-term fertilization. Our previous study further found that the balanced points of soil organic matter differed significantly under various fertilization regimes, whereas the reason resulted in the differences is uncertain. Thus, to find out the reason contributed to different balanced points of soil organic matter under different fertilization regimes, this program was designed based on a long-term fertilization experiment with winter wheat-soybean rotation system situated in the lime concretion black soil at Mengcheng County, Anhui Province. In the present program, four C pools including the silt-clay protected pool, soil microaggregate-protected pool, the biochemically protected pool and the non-protected C pool would be analyzed to investigate the reason contributed to different balanced points of soil organic matter under different fertilization regimes. In addition, 13C labeling chamber would be constructed to gain 13C labeled wheat and alfalfa in this program. The technique of 13C abundance combined with soil incubation method would be employed to explore the influence of exogenous organic material quality on soil microbial community structure and organic matter accumulation. After adding 13C labeled wheat and alfalfa straw into soils with different balanced points of soil organic matter and incubating for 120 days, the regulatory mechanism involved in the balanced points of soil organic matter under different fertilization regimes was investigated. Based on the above results, this program would provide an important data to guide the fertilizer management and help to develop a sustainable agriculture with high productivity.

施肥能够提高土壤有机质水平，但连续施肥20年后砂姜黑土有机质达到了平衡。由于不同施肥模式下砂姜黑土有机质平衡点存在显著差异，而造成这种差异的原因目前还不清楚。因此，为了探明不同施肥模式下有机质平衡点差异的形成原因，本项目拟利用安徽蒙城砂姜黑土长期定位试验（小麦-大豆轮作）分析土壤粉粒-粘粒保护有机质、团聚体保护有机质、生物化学保护有机质和自由态有机质四个组分含量对不同施肥模式下有机质平衡点的影响；同时，采用室内培养和碳同位素示踪技术，通过对不同平衡点水平土壤在添加13C标记小麦和苜蓿后微生物群落结构和有机质累积效率变化的分析，探明外源有机物质量，微生物群落和土壤有机质累积效率三者之间的响应关系，进而揭示长期不同施肥模式下土壤有机质平衡点差异的形成机制，从而为砂姜黑土分布区农田土壤培肥管理措施的制定提供科学理论基础。

砂姜黑土是安徽省主要的中低产土壤之一。农业施肥管理措施能够提高砂姜黑土土壤有机质，然而长期施肥管理措施对土壤有机质的提升作用存在临界点，过去的研究发现连续施肥20年后土壤有机质将达到一种平衡，且不同施肥模式下土壤有机质平衡点存在差异。针对砂姜黑土土壤有机质平衡点和不同施肥模式下有机质平衡点差异的形成问题，本项目通过砂姜黑土长期定位试验开展了不同施肥模式下土壤团聚体组分及其有机质含量、土壤有机质功能团组成和微生物群落结构及功能群变化的研究。研究结果表明，长期施肥管理措施降低土壤中粒径>2 mm的团聚体组分百分含量，提高土壤中粒径<0.25 mm团聚体组分含量，同时在有机质平衡点较高的牛粪处理土壤中粒径<0.25 mm的团聚体组分中有机质含量显著高于其他处理。同时，研究结果还表明不同施肥处理模式对于土壤有机质不同功能团含量的影响并不显著，这说明长期施肥管理措施降低了土壤大团聚体对有机质的物理保护作用，有机质结构和化学稳定性与土壤有机质平衡点水平不存在相关性。在土壤微生物群落组成和功能群组成方面，本项目通过分析发现不同施肥模式下土壤细菌和真菌群落结构存在显著差异，且施肥模式改变微生物群落对环境因子变化的抵御能力和作物轮作下的微生物功能群组成。其中，牛粪处理能够提高小麦收获期后土壤丛枝菌根真菌（Arbuscular mycorrhizal fungus，AMF）相对多度，秸秆还田则提高大豆收获后土壤AMF相对多度。最后，项目还增加了施肥模式对土壤碳代谢功能基因丰度的影响研究，研究发现大豆收获后相比不施肥处理，秸秆还田，牛粪添加和单施无机肥均降低了土壤碳代谢功能基因丰度，这表明在有机质平衡点较高的土壤中微生物的碳代谢活性较低。研究结果为砂姜黑土区不同施肥模式下有机质平衡点差异形成的原因提供了理论依据，同时为农田土壤有机质的提升和相关技术的研发提供了科学数据支撑。