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不同类型土壤团聚体力稳性对前期含水率的差异化响应

Differential response of aggregate mechanical stability to antecedent water content for different types of soils

  • 摘要: 为探讨土壤含水率对团聚体力稳定性的调控机制,该研究选取4种典型耕作土壤(黑土、褐土、红壤和砖红壤),通过控制试验建立4%~20%含水率梯度,采用抗压试验测定不同含水率下团聚体抗张强度、破碎能量和易碎性指数,进而揭示成土环境差异背景下前期含水率对团聚体力稳定性的影响规律。结果表明:抗张强度和破碎能量与前期含水率呈指数函数关系(R2=0.70~0.98,P<0.05);其中黑土和褐土的抗张强度和破碎能量随含水率增加而快速下降,而红壤和砖红壤的抗张强度和破碎能量变化则较为平缓;线性回归分析表明,易碎性指数与游离态铁铝氧化物呈正相关关系(R2=0.91~0.94,P<0.05),团聚体力稳性指标抗张强度和破碎能量对含水率的敏感性指数与蛭石和交换性钙离子呈负相关关系(R2=0.94~0.98,P<0.05),表明黏土矿物类型与盐基离子组成的协同作用调控着团聚体力学响应的水分敏感性特征,其作用强度随成土发育进程呈现显著衰减规律。对于黑土和褐土等对前期含水率敏感的土壤,农业耕作应严格控制含水率以减少团聚体破碎,同时可通过增施含钙改良剂等措施降低其水分敏感性,研究结果为不同区域农田土壤质量管理提供理论支持。

     

    Abstract: Aggregate mechanical stability represents the aggregates' capability to endure mechanical forces that tend to break them apart and is an essential index for appraising soil quality. Aggregate mechanical stability is influenced by both intrinsic soil properties and external factors. Most previous studies focused on a single soil type and the conclusions of different studies were different. To date, there is still a lack of systematic research on the response characteristics of aggregate mechanical stability to antecedent water content in different soil types. In this study, we collected four typical cultivated soils from the major agricultural regions in eastern China, that is, Black soil, Cinnamon soil, Red soil and Latosol. Compression test was conducted to determine the tensile strength, specific rupture energy and friability index of soil aggregates at different antecedent water contents (4%, 6%, 8%, 10%, 12%, 15% and 20%); the relationship between the tensile strength, specific rupture energy and friability index of these aggregates and the physicochemical properties of the soils were analyzed to identify the influencing factors. The results showed that tensile strength and specific rupture energy were mainly affected by the antecedent water content (F=99.6 and 43.9), followed by soil type (F=28.3 and 21.9). Both indices overall decreased with antecedent water content in different manners, which could be well characterized by an exponential function relationship (R2=0.70~0.98, P<0.05). The value of parameter β of the exponential function reflects the sensitivity of the aggregate mechanical stability to the antecedent water content. For Black soil(βY =-0.15,βEsp =-0.19) and Cinnamon soil(βY =-0.18, βEsp =-0.31), The tensile strength of aggregates and the specific rupture energy declined swiftly as the soil water content rose, while for Red soil(βY =-0.07, βEsp =-0.05) and Latosol(βY =-0.06, βEsp =-0.06), they varied gently. Among soil types, Cinnamon soil had the greatest aggregate mechanical stability (Y=141.53kPa,Esp=14.31J/kg); except for Latosol, the friability index of Black, Cinnamon and Red soil aggregates were significantly higher at >10% than <10% antecedent water contents. Regression analysis showed that parameter α was negatively correlated with amorphous manganese oxide and 1.4 nm transition minerals (R2=0.95~0.99, P<0.05), and positively with exchanged calcium ions (R2=0.87, P<0.05); parameter β was positively correlated with amorphous manganese oxide and 1.4 nm transition minerals (R2=0.88~0.99, P<0.05), and negatively with exchangeable calcium ions and vermiculite contents (R2=0.94~0.98, P<0.05); friability index has a significant positive correlation with the content of free iron and aluminum oxides (R2=0.91~0.94, P<0.05), and a negative one with silt content(R2=0.92, P<0.05). For different types of soils, amorphous manganese oxide, free state iron and aluminum oxides can weaken the sensitivity of aggregate mechanical stability to antecedent water content, which is opposite to silt, exchangeable calcium ions, and vermiculite. In conclusion, as controlled by inorganic cementing agents, the sensitivity of aggregate mechanical stability to soil water content decreases with the increase of soil development. The obtained results will be of great significance to reveal the characteristics and mechanisms of aggregate mechanical stability against environmental changes and facilitate the scientific managements of soil quality in different agricultural regions .

     

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