保水剂-土壤多相体系中团聚体形成及水分传导的互作机理

Super-absorbent polymers (SAPs), one of new water-saving materials, have been widely adopted in agriculture production. The crosslinking properties of SAPs determined their applications would alter the pore distribution and aggregate structure of soil. Our previous researches showed that the uneven pores on saturating SAPs' surface were affected by soil particle, and the soil aggregate formation was limited by the SAPs' network structure. But the interaction mechanism of soil aggregate formation and soil moisture conduction in the multiphase system of SAPs and soil are unknown. In this project, the analytical tools as electron microscopy and scanning electron microscope, and so on, were all used through a series of simulation experiments. Based on the previous research, the aperture changes on the SAPs' surface under different water potential gradient were studied to illuminate their water availability. The influences of soil water exchange and conduction between soil and SAPs were compared and analyzed in view of three levels, as the effect of SAPs on soil, the effect of soil on SAPs, and the interaction of soil and SAPs. The influences of SAPs on the distribution and stability of soil aggregate were studied to verify the relationship between soil aggregate formation and water conduction, to state the combination pattern and effect intensity of SAPs and soil mineral crystal, to reveal the physicochemical mechanisms of water supply with SAPs' application. The research may provide the theoretical support for reasonable application of SAPs and farmland water management.

保水剂是当前应用最为广泛的化学节水制剂之一，保水剂自身交联特性决定了其施入土壤必将改变土壤的孔隙分布和团聚体结构。申请人研究发现，吸水饱和的保水剂表面孔隙分布受土壤颗粒影响，而土壤团聚体的形成也受保水剂高分子网状结构制约。目前关于保水剂-土壤之间水分传导和团聚体作用机制方面的研究较少，本项目在前期研究的基础上，基于电子显微镜和扫描电镜等分析手段，通过模拟试验，研究不同水势梯度下保水剂表面孔径的变化，阐明保水剂中水分的有效性；并比较分析保水剂对土壤、土壤对保水剂，以及保水剂-土壤多相体系中水分交换和传导的直接作用；研究保水剂对土壤团聚体分布和稳定性的影响，明确保水剂与土壤颗粒矿物晶体之间的作用方式；阐明团聚体形成与土壤水分传导的关系，揭示保水剂供水的物理化学机制；以上研究将为保水剂的合理应用和农田水分管理提供理论依据。

干旱缺水和土壤退化是制约我国农业可持续发展的重要因素之一，应用化学节水材料是解决上述问题的有效途径之一。本研究以农业应用较为广泛的保水剂为研究对象，以明确保水剂-土壤多相体系中团聚体形成与水分传导的互作机理为目标，通过一系列盆栽和土柱试验，模拟自然蒸发脱湿过程，比较不同类型土壤水分对保水剂结构和形态的影响，保水剂对土壤团聚体形成和稳定性的作用，以及保水剂-土壤多相体系的水分传导和互作效应。主要结果和结论如下：1) 基于全反射红外光谱和环境扫描电镜分析发现，干湿交替环境中，不同用量保水剂与砂土混合后，土壤中的Si－O－Si键、－OH、蒙脱石矿物、以及无定形氧化硅等矿物胶体会进入保水剂的三维网状结构中，使保水剂的膜结构产生不均匀的褶皱，甚至破裂；而且保水剂用量越大，二者之间的反应越剧烈。初步认为土壤黏粒矿物与保水剂发生不同程度的化学反应是导致保水剂随使用时间延长吸持水能力降低的主要原因之一。2) 施用保水剂后，土壤的液相比显著增加，气相比相对减少，同时增多了土壤中、小孔径的孔隙数量；而且保水剂用量越大，对土壤三相比和土壤孔隙的作用越显著，据此认为保水剂适用于大孔隙较多的土壤。3) 研究所用聚丙烯酸钠保水剂用量越大，其改变土壤持水能力的效果也越明显，但影响趋势会随着失水次数的增加而减弱；在土壤水吸力降低的过程中，保水剂能够减缓土壤含水量降低的速度。在土壤极度干旱的条件下，保水剂不仅不能增强土壤比水容量，反而使土壤的供水能力降低；当土壤处于轻度干旱时，保水剂能显著提高土壤供水能力，但供水能力会随着保水剂用量的增加而减弱。分析认为保水剂对土壤供水能力的影响与保水剂的用量和土壤的干湿状况有关。4) 保水剂能够增强土壤团聚体的水稳性以及平均粒径的团聚度。土壤中<0.053 mm的水稳性微团聚体受保水剂的交联作用，会黏结形成更加稳定的水稳性大团聚体，进而减小因土壤干湿交替对团聚体产生的破坏。