生物炭施用与微咸水灌溉对滨海盐渍土结构内力驱动作用的影响

Effects of Biochar Application and Brackish Water Irrigation on Internal Force-driven Mechanisms in Coastal Saline Soil Structure

摘要:

生物炭可防治微咸水灌溉下土壤结构劣化风险，但其微观、介观尺度上的作用机理尚不完全明晰。本研究选取江苏省典型滨海盐渍土，设置4种生物炭施用处理（0、10、20、30t/hm2），开展了不同电导率（EC，0.5、1、3、5dS/m）和钠吸附比（SAR，0、15、30、∞（mol/L）1/2）的16组微咸水入渗试验。结果表明：随生物炭施用，土壤pH值和有机碳含量增加0.7%~2.7%、130.7%~675.7%，并显著影响了颗粒表面性质（p<0.05），土壤阳离子交换量、比表面积、表面电荷密度和哈梅克常数分别增大20.0%~88.2%、10.7%~30.0%、8.4%~44.7%、35.6%~62.8%。入渗溶液EC减小、SAR增大均可提高表面电位和静电排斥力，同时随生物炭施用，不同EC和SAR溶液界面颗粒表面电位和颗粒间静电排斥力分别增加0.47%~17.65%、0.16%~14.45%，但范德华引力亦增加35.61%~62.81%，导致净斥力随生物炭施用先减后增，10、20、30t/hm2处理较0t/hm2减小9.39%~147.43%、15.31%~219.55%、9.69%~217.13%。土壤孔隙度、连通孔占比、大孔隙（等效直径大于等于1mm）占比等与净斥力呈显著负相关（p<0.001），随净斥力减小分别增加7.60%~40.90%、0.15%~34.37%、3.78%~43.09%，致使不同微咸水入渗溶液下，10、20、30t/hm2处理饱和导水率提升7.77%~24.70%、15.15%~31.60%和10.81%~28.22%。综上，本文探究了生物炭施用下盐渍土表面性质、内力作用、孔隙结构及水分运动间的传递影响，20t/hm2生物炭对土壤结构劣化的调控效应最佳，可为微咸水安全利用提供科学依据。

Abstract:

Biochar can mitigate the risk of soil structure degradation under brackish water irrigation, but its mechanisms of action at the micro- and mesoscale remain unclear. Selecting typical coastal saline soils in Jiangsu Province, totally four biochar application treatments (0t/hm2, 10t/hm2, 20t/hm2, 30t/hm2) were established, and brackish water infiltration experiments under 16 different electrical conductivity (EC, 0.5dS/m, 1dS/m, 3dS/m, 5dS/m) and sodium adsorption ratios (SAR, 0(mol/L)1/2, 15(mol/L)1/2, 30(mol/L)1/2, ∞ (mol/L)1/2) were conducted. The results showed that with the application of biochar, soil pH value and organic carbon content significantly increased by 0.7%~2.7% and 130.7%~675.7%, respectively, and significantly affected particle surface properties (p<0.05). The cation exchange capacity, specific surface area, surface charge density, and Hamaker constant of the soil was increased by 20.0%~88.2%, 10.7%~30.0%, 8.4%~44.7%, and 35.6%~62.8%, respectively. Reduced EC and increased SAR of the infiltration solution both enhanced surface potential and electrostatic repulsion. Additionally, with biochar application, particle surface potential and interparticle electrostatic repulsion was increased by 0.47%~17.65% and 0.16%~14.45%, respectively, under different EC and SAR solution interfaces. However, van der Waals forces were also increased by 35.61%~62.81%, resulting in a decrease followed by an increase in net repulsive force with biochar application. Compared with the 0t/hm2 treatment, the 10t/hm2, 20t/hm2, and 30t/hm2 treatments showed decreases of 9.39%~147.43%, 15.31%~219.55%, and 9.69%~217.13%, respectively. Soil porosity, connected pore fraction, and large pore (equivalent diameter greater than or equal to 1mm) fraction showed a significant negative correlation with net repulsive force (p<0.001), increasing by 7.60%~40.90%, 0.15%~34.37% and 3.78%~43.09%, respectively, as net repulsive force decreased, which increased the saturated hydraulic conductivity by 7.77%~24.70%, 15.15%~31.60%, 10.81%~28.22% under different brackish water irrigation solutions for the 10t/hm2, 20t/hm2 and 30t/hm2 treatments respectively. In summary, the interactive effects of surface properties, internal forces, pore structure, and water movement in saline soils under biochar application were investigated. The 20t/hm2 biochar treatment exhibited the optimal regulatory effect on soil structure degradation, providing scientific basis for the safe utilization of brackish water.