Study On The Release Law And Influencing Factors Of Soil Colloid In Typical Cultivated Land Of Yellow Soil In Guizhou During Rainy Season

The rapid and long-distance migration of colloid-assisted pollutants is one of the important challenges facing the current water environment protection.Due to the high content of soil clay,the rapid surface runoff and the possibility of underground leakage in the karst yellow soil area,caused the water environment risk of colloid-assisted pollutant migration greater.Therefore,the basic goal of the study is to quantitatively reveal the dynamic release law of soil colloids and its key influencing factors in the typical yellow soil area of Guizhou during the rainy season through experimental analysis.In this study,the medium-depth tillage conditions of traditional non-tillage and fine tillage were compared.The evolution characteristics of soil basic physical and chemical properties in different periods of rainy season,the concentration,particle distribution and dynamic evolution of soil colloid outflow under rainfall-infiltration conditions,and the dynamic changes and interactions of key influencing factors of colloid release accompanied by colloid outflow were carried out.The main conclusions are as follows.(1)Dynamic changes and differences of soil physical and chemical properties.The soil bulk density and clay and silt content showed a decreasing trend in the surface 10 cm with the passage of sampling time,and the changing rate of ploughed soil was significantly higher than that of non-ploughed soil.The saturated hydraulic conductivity generally showed a gradual decrease,but the second non-ploughed soil showed a larger hydraulic conductivity due to the presence of macropore preferential flow.The p H value also showed a decreasing trend,the soil conductivity increased first and then decreased,and the soil organic matter content decreased first and then increased in the surface layer of 0-10 cm.The above soil physical and chemical properties were also significantly different between tillage and non-tillage conditions,surface 0-5 cm and subsurface 5-10 cm.The reason is that the previous precipitation and tillage caused a series of physical,chemical and biological effects.(2)Dynamic characteristics of soil colloid outflow concentration and particle size.The increase of colloid outflow concentration in newly ploughed soil was not prominent compared with that in ploughed soil,but the colloid outflow concentration and cumulative outflow increased prominently with time,which was close to 2 times that of non-ploughed soil.The colloidal particle size distribution showed unimodal or multimodal characteristics except for the initial large-particle influence,and the rest showed bimodal characteristics overall,and the peak was mainly distributed around10 μm or less than 10 μm.The peak particle size,mean particle size,median value and interquartile range of ploughed soil were significantly smaller than those of non-ploughed soil,and had a smaller fluctuation level,indicating that its specific surface area was further increased,the ability to adsorb pollutant migration was further enhanced,and the process was more stable.The precipitation in the early stage also has an important influence on the migration of soil colloids.It may have a higher colloid outflow concentration in the early stage of the next rainfall infiltration process,but that of the non-ploughed soil will decay rapidly,while the ploughed soil can be stable or even increase.(3)The dynamic change characteristics and interaction of key influencing factors.Ploughed soil showed higher p H value,DOC,electrical conductivity and calcium and magnesium ion concentration during the three adoptions.There was a significant positive correlation between the colloidal effluent concentration and the influencing factors in the second and third sampling of non-ploughed soil.The first non-ploughed soil and the second ploughed soil showed a strong negative correlation.There was no significant correlation between the colloidal effluent concentration and the analyzed influencing factors in the first and third samples of ploughed soil.And the characteristic particle size of the colloid was significantly positively correlated with the content of related influencing factors.The reason is that under different early rainfall,soil texture and pore structure conditions,some columns of soil colloid outflow characteristics are significantly different.However,it should be noted that the attenuation of colloidal characteristic particle size is also affected by the gradual deposition of large particles during infiltration,which blocks the gap channel and causes its initial rapid decrease,so the relationship between the two needs to be further explored.The study revealed the dynamic release law of soil colloids in yellow soil cultivated land,and clarified that it was affected by the basic physical and chemical properties of soil,the previous precipitation and a series of physical,chemical and biological activities.The relevant results laid an important foundation for the quantitative evaluation of the migration characteristics of pollutants carried by soil colloids under the condition of sloping farmland in yellow soil area and the risk of regional water environment pollution,especially the risk of groundwater pollution.