Several Zonal Soils Organic Matter Composition And Its Relationships With Structural Stability

As an important part of soil,organic matter is very complex,which is effected by many factors.Organic matter is an important component of soil aggregates and can seriously affect soil structure.Soil erosion is one of the main environmental problems in China.Soil erosion resistance usually can be measured by soil erodibility.The zonal soils(cinnamon,yellow cinnamon,brown red soil,red soil,latosolic red soil and laterite)developed from similar parent material(quaternary clay materials)were selected as study objects in this study.The distribution regularity of organic matter in different aggregates of zonal soils and the soil structural stability characteristics of several zonal soils in warm temperate zone,tropical and subtropical regions and their difference were the main research content.The relationship between composition of organic matter and the soil erodibility and water aggregate stability was studied in the research to provide theoretical support for soil erosion prediction.The main work and conclusions in this paper included:(1)Soil properties were affected by soil formation process.From north to south,with soil leaching gradually increased,the pH and CEC of soil gradually reduced.With the degree of soil weathering and the desilication aluminized role gradually deepened,the iron aluminum oxide presented stata of enrichment.The texture of tested soil was sticky.From north to south,the hydrothermal conditions were gradually enriched,the eluviation was enhanced,and the clay contents in the whole soil and different aggregates were gradually increased.The soil bulk density was gradually decreasing from north to south.Compared with the wasteland,the soil bulk density was generally smaller.The capillary porosity of tested soil was higher than aeration porosity.(2)The total organic matter content in microaggregates was relatively lower.The absolute contents of each component of organic matter were higher in surface layer.The distribution of most components in different soil types was not obvious,and FA and HMr were increasing from north to south.FA,HMi and HMr were roughly expressed as wasteland>forest land.The HA contents of microaggregates were higher than large aggregates,while FA,HMi and HMr were opposite.From north to south,the relative content of FA increased,while the relative contents of HA,HMi,HMc and HMr decreased,and the complexity of organic matter decreased.The newly formed organic matter was mainly FA.The relative contents of most components(FA,HA,HMi,HMc)in microaggregates were larger than them in macroaggregates,and macroaggregates contained more active organic carbon.The relative content of FA in forest was lower than that of wasteland and HMr were opposite,and the organic matter structure of woodland was more complicated than that of wasteland.The relationship between the proportions of the components of the organic matter was HMi < HMc < HA < FA < HMr.The total organic matter were similar as the absolute value of each component.(3)The humification degree of the soil decreased with the increasing of the depth,and the PQ value of the microaggregates was larger than that of the macromolecules,and gradually decreased from north to south.Northern soil was conducive to the accumulation of HA,and surface soil and microaggregates were also more conducive to the preservation of HA.The ratio of HMi and HMc in laterite was relatively higher than that in other regions.The proportion of soluble HM from north to south gradually decreased,the subsurface soil layer is more conducive to the accumulation of soluble humin,and the formation rate of soluble humin in microaggregates was greater.(4)Cinnamon soil and yellow cinnamon soil had more microaggregates,but the water stability of macroaggregates was poor.Red soil,latosolic red soil and laterite had more macroaggregates and less microaggregates.From north to south,the stability of soil microaggregates and macroaggregates increased gradually.And the water stability of macroaggregates in the surface soils was better than that in the subsurface soils.(5)The accumulation of total organic matter in the soil,especially in the microaggregates,could improve the stability of macroaggregates.The accumulation of FA in total organic matter was favorable to the stability of microaggregates.The accumulation of HMc in the total organic matter of microaggregates and the accumulation of HMi and HMc in the total organic matter in the soil were beneficial to improve the stability of microaggregates,expecially the accumulation of HMc in the microaggregates.Most organic matter components and relative values had a strong direct negative effect on CDI,but only the increase of FA relative value could significantly reduce the dispersion of microaggregates after synthesizing all the roles.The increase of HA content in the soil,especially in the microaggregates,could enhance the stability of macroaggregates.The increase of FA content and relative value was helpful for the improvement of the stability of macroaggregates,and the effect of FA in macroaggregates was greater.The increase of the content of three kinds of humin could enhance the stability of macroaggregates,and the improvement of the increase of HMc content in the macroaggregates and the increase of HMr content in the microaggregates were more obvious.(6)Soil erodibility process is complex and changeable.The soil erodibility of cinnamon soil was the largest,followed by red soil and latosolic red soil,and it of the laterite soil was the smallest.The soil erodibility showed the first to reduce and then increase and last reduce the trend from north to south.The increase of FA content and relative value in microaggregates could reduce soil erodibility,and the increase of HA content in microaggregates and the accumulation of HMi in total organic matter in the macroaggregate also contributes to the reduction of soil erodibility.