潮土秸秆碳氮高效利用机理和途径及其对土壤孔隙和团聚结构的影响

Huang-Huai-Hai Plain locates in the northern China and is an important food supply area in China. In this area, the typical soil is classified as fluvo-aquic soil, soil carbon and nitrogen content is generally low and difficult to accumulate, moreover, the high content of sand in fluvo-aquic soil makes it difficult to form favorable pore and aggregate structure. A long-term fertilization experiments lasted for 30 years showed that the contents of soil carbon and nitrogen were difficult to improve continually with application of chemical fertilizer (total nitrogen content was difficult to break through 0.6g/kg, and soil organic matter content was difficult to increase to more than 10g/kg), however, the long-term application of organic fertilizers from straw decomposition without increasing the amount of nitrogen application, could break through the barriers of chemical fertilizer application, and further significantly continuously enhance the fertility and crop yield. In this proposed project, pot experiments, laboratory culture experiments and field experiments will be conducted, and a series of modern techniques such as isotope labeling, scanning electron microscope-X energy dispersive spectrometer(SEM-EDX), High-resolution magic angle spinning.nuclear magnetic resonance (HR-MAS NMR), and high-throughput sequencing will be applied together to investigate the mechanisms for carbon and nitrogen release and microorganism driving during the degradation process in straw of winter wheat and summer corn, meanwhile, the response characteristics of soil pore and aggregate nutrient availability in crop during the process of straw degradation will be also clarified, moreover, this mechanisms will also been studied under the conditions of adding different activators. In addition, field experiments with different time scales will be conducted. Such efforts not only contribute to our further screening and optimizing the way in returning of straw, but also provide theoretical basis and technical support for the soil fertility cultivation of the Huang-Huai-Hai Plain.

黄淮海平原潮土区土壤碳氮含量普遍较低且难于累积，砂粒含量高使得土壤难以形成良好的孔隙和团聚结构。中国科学院封丘农田生态试验站里长达30年的长期施肥试验表明仅施用化肥难于持续提升土壤碳氮含量（全氮含量难以突破0.6g/kg，有机质难以提升到10g/kg以上）和作物产量，而长期施用秸秆腐熟的有机肥处理能在不提高施氮量的前提下，突破化肥施用的壁垒而持续提升潮土肥力和作物产量。因此，本项目通过野外盆栽、室内模拟以及大田长期定位试验，利用同位素示踪、扫描电镜-X射线能谱仪结合（SEM-EDX）、高分辨魔角核磁共振（HR-MAS NMR）、高通量测序等技术来研究冬小麦-夏玉米秸秆及其在不同激发调节剂作用下的碳氮释放规律和微生物驱动机制，阐明秸秆降解过程中的土壤孔隙和团聚体响应特征，明确养分有效性，并建立不同时间尺度的田间试验，以期为筛选优化秸秆还田方式持续提升土壤地力提供理论依据和技术。

黄淮海平原潮土区土壤碳氮含量普遍较低且难于累积，砂粒含量高使得土壤难以形成良好的孔隙和团聚结构。中国科学院封丘农田生态试验站里长达30年的长期施肥试验表明仅施用化肥难于持续提升土壤碳氮含量（全氮含量难以突破0.6g/kg，有机质难以提升到10g/kg以上）和作物产量，而长期施用秸秆腐熟的有机肥处理能在不提高施氮量的前提下，突破化肥施用的壁垒而持续提升潮土肥力和作物产量。因此开展潮土秸秆碳氮高效利用机理和途径及其对土壤孔隙和团聚结构的影响研究，结果表明：（1）与秸秆移除相比，秸秆深还处理显著提升0-40cm 有机质及其组分、全氮、硝态氮、铵态氮、颗粒态有机氮和矿物结合有机氮含量。秸秆深还显著提高小麦产量6.02%，玉米产量5.84%。且秸秆深还配施16%有机肥处理下土壤碳氮组分及作物含量效果最佳。（2）五种外源不同激发剂物料（生化黄腐酸、生物炭、褐藻寡糖、微纤维岩棉、硅藻土）均可以有效提高玉米秸秆的降解率与降解速率且在前100天促进效果最为显著。能改善土壤结构，适量浓度的外源物料能增加玉米生长，但添加量过高的处理会抑制玉米生长。生化黄腐酸以土重0.5%为宜，生物炭以土重0.5%为宜，褐藻寡糖以土重0.5%为宜，微纤维岩棉以土重1%为宜，硅藻土为土重的2%效果最好；综合秸秆降解、养分释放、玉米生长以及成本，推荐添加比例为土重0.5%和1%的微纤维岩棉；（3）在秸秆降解过程中，随着长期施氮水平的升高秸秆的降解效率也就随之增大。土壤无机氮素含量的增加，促进了某些富营养型细菌的生长发育，抑制了某些贫养型细菌的生长发育，进而改变了两者之间丰度的相对比例，导致土壤细菌群落发生改变；（4）在秸秆还田基础上施入部分有机氮肥能激发还田秸秆效用，并推荐“秸秆还田+有机肥替代部分化肥氮”处理作为农田最佳管理措施。有机肥替代部分化肥氮能显著增加土壤有机碳含量，稳定团聚体中有机碳，起稳定土壤有机碳作用，并能增强土壤团聚体结构稳定性，有利于提升农田土壤固碳能力。