Analysis On Soil Erosion Characteristics Of Typical Gentle Slope Arable Land Of Black Soil

Mollisol degradation continues to deteriorate,which is the only farmland ecosystem in China.Failure to protect black land in a timely manner would significantly undermine regional food production capacity and regional ecological functions and pose a serious threat to national food security.Therefore,it is urgent to reveal the occurrence and development law of soil erosion under the interaction of multiple external forces on the slope surface in the mollisol area,and clarify the influence of black soil structure characteristics on the slope erosion process.Straight slope,concave slope and concave-straight composite slope farmland with slope length of 1020 m in Keshan Farm were selected.The ¹³⁷Cs tracer technology and wavelet analysis theory were used to estimate the modulus of soil erosion on the slope,and the change law of soil erosion intensity along the slope length in the past 70 years was explored.The fragmentation mechanism of mollisol aggregates under different conditions（rainstorm,light rain,disturbance）were distinguished by LB method,and the variation characteristics and influencing factors of soil aggregate stability under different tillage layers were quantitatively analyzed,in order to provide data support for the development of accurate water conservation measures and the realization of soil nutrient management in the region.The main conclusions are as follows:（1）The spatial variation of soil erosion intensity was studied by wavelet analysis method based on the analysis of ¹³⁷Cs content on typical long gentle slope farmland in mollisol area of northeast China.The results showed that there were different degrees of soil erosion in different slope types of cultivated land in the same area.The average annual erosion rate of straight slope(3040 t·km^-2·a^-1)<the composite slope(3395 t·km^-2·a^-1)<the concave slope(4220 t·km^-2·a^-1).There were strong-weak alternate cycles of erosion in the whole slope of cultivated land on long gentle slope.There were 380 m,300 m and 250 m cycles of slope length in the sampling range of straight slope,composite slope and concave slope.Through the mathematical fitting of slope erosion rate along the slope length,it is found that the sine curve function fitting can better characterize the periodic law of slope erosion rate of cultivated land on long gentle slope in typical mollisol area.（2）The composition and stability of soil aggregates are one of the key indicators for evaluating soil quality and soil erosion.Under the three treatments of LB method,soil aggregate fragmentation under rapid wetting treatment was mainly 0.1-0.05 mm.Soil aggregates after slow wetting treatment were mainly>2 mm aggregates;after mechanical disturbance treatment,soil aggregates were mainly 1-0.5 mm.Under different treatments,the aggregate stability showed MWD_SW>MWD_WS>MWD_FW.The sensitivity of soil aggregates in each tillage layer to the disturbance of three different treatments was rainstorm>plowing>light rain.Under the three damage mechanisms,MWD_0-10cm<MWD_10-20cm<MWD_20-30cmbetween different soil layers was reflected.（3）Under the action of rainfall and runoff,the fragmentation and dispersion of aggregate particles are the most important links of soil erosion.Under the hydraulic driving force,the aggregates on the surface soil slope are mainly broken into 1-0.2 mm particles,which provide materials for raindrop splash erosion and runoff scouring,and become the main source of erosion materials in the process of soil erosion.As a result,the organic carbon enriched in the soil surface was stripped and migrated with the hydraulic and tillage erosion,and then redistributed on the slope.In this process,the soil nutrient content produced a large amount of loss,which decreased the overall fertility and water retention of the soil.It reflected that the distribution trend along the slope was opposite to the change trend of soil erosion rate on the slope,and the soil nutrient content was corresponding to the soil erosion rate.It reflects the response relationship between the distribution of soil nutrient loss on slope and the change of soil erosion rate on slope.（4）Soil erodibility in the study area was between 0.008 and 0.043,with an average of0.018,belonging to medium variation（16%<CV<32%）.The K value of straight slope was the smallest and the variability was the smallest（14.8%）in different slope forms.The K value of compound slope was similar to that of concave slope,and the variability was 22.4%and 21.0%,respectively.With the increase of soil depth,the K value of soil erodibility decreases obviously.The grain size of>1 mm has strong ability to resist erosion medium stripping and transportation,and has strong influence on the K value of soil erodibility.Erodibility K value was significantly negatively correlated with organic carbon content,indicating that soil organic carbon can increase the bonding between soil particles and water,promote water stability and the formation of microaggregates,which is conducive to the stability of soil structure and enhance soil erosion resistance.