覆盖作物根系生长对土壤压实的缓解机制研究

Nowadays, soil compaction induced by operation of machinery has been harming the sustainable development of agriculture. Using a crop rotation which includes strong rooting cover crops has been proposed as a means to alleviate soil compaction, however, its mechanism is still unclear. Using technological means such as X-ray computed tomography (CT) and low-field nuclear magnetic resonance relaxometry, this project will combine field experiment and laboratory simulated experiment to study mechanism of cover crop rooting on alleviating soil compaction. Firstly, field experiment will be conducted to study root architecture of cover crops in compacted soil for clarifying the the response of root architecture of cover crops to compacted soil; to investigate variation of physical properties of compacted soil before and after cover crop plantation and root architecture of following crop for revealing the improving effect of cover crop plantation on soil structure and growth of following crop. Meanwhile, laboratory simulated experiment will be carried out to investigate variation of physical properties of compacted soil induced by addition of root exduations for illustrating the influence mechanism of root exudations on soil physical properties. The achievements of this project will provide scientific evidence for alleviating soil compaction, arranging reasonable crop rotation system, and prompting sustainable development of agriculture.

集约化农业下机械作业造成的土壤压实日益严重，危害农业可持续发展。轮作根系发达的覆盖作物是缓解土壤压实的有效手段之一，但其作用机制尚不明确。本项目将采用X射线计算机断层扫描（CT扫描）和低场核磁共振等技术手段，结合田间实验和室内培养实验，系统研究覆盖作物根系对压实土壤的缓解机制。首先通过田间实验，研究压实条件下覆盖作物根系特征，明确不同覆盖作物的根系结构对土壤压实的响应；其次，研究覆盖作物种植前后压实土壤物理性质的变化以及后茬作物根系特征，揭示覆盖作物种植对土壤结构的改善作用及其对后茬作物生长的影响；同时，建立室内模拟实验研究根系分泌物添加后，压实土壤物理性质的变化规律，阐明分泌物对土壤物理性质的影响机制。本项目成果将为缓解土壤压实，构建合理的种植制度，推进农业可持续发展提供科学依据。

随着农业现代化的推进，农业机械的使用日益增多，造成的土壤压实退化问题日益严重，阻碍粮食作物生长，威胁我国粮食安全。传统的机械深松等措施存在能耗高、时效短、二次压实风险高等不足之处，利用覆盖作物根系的生长作用改善土壤结构，消减土壤压实，从而提升压实土壤生产力，是非常具有应用前景的技术措施。本项目将研究不同覆盖作物根系对压实土壤的响应，覆盖作物对压实土壤物理性质的改善作用以及对后茬玉米生长的影响，再研究孔隙结构对玉米根系生长的影响，从而揭示覆盖作物消减土壤压实的机制。本项目通过田间实验明确了萝卜毛苕子混播对压实土壤的适应性更好，具有较好的缓解土壤压实的潜力。发现了覆盖作物种植降低土壤含水量，但对土壤容重影响较小；苜蓿可以有效增加压实和不压实土壤的导气率。种植覆盖作物有效促进压实土壤中后茬玉米根系的生长，但对不压实土壤中玉米根系无影响。萝卜毛苕子混播和油菜种植有利于压实土壤后茬玉米产量的提升，但对不压实土壤玉米产量影响较弱。室内模拟实验发现压实土壤中玉米根系以占领模拟孔隙为主，不压实土壤中玉米根系以穿过模拟孔隙为主；2 mm的模拟孔隙不能促进玉米根系生长，主要是由于模拟孔隙孔径大于玉米根系，导致根系与孔隙接触不良。进一步研究发现，1 mm和0.5 mm孔径的模拟孔隙有利于促进玉米苗期根系生长；在0.5 mm孔径下，每个土柱20个孔隙对玉米生长的促进作用大于每个土柱5个和80个孔隙。根据以上研究，提出了生物耕作的新观点，利用根系穿透能力强的覆盖作物改善压实土壤结构，促进作物生长。本项目研究成果将为调控土壤结构退化，提升粮食产量，推进农业可持续发展提供理论和技术指导。