Impacts Of Soil Erosion And Deposition On Soil Properties And Corn Yield In The Thin Layer Black Soil Region

Severe soil erosion causes soil quality degradation and crop yield decline,and threatens agricultural sustainability in the Northeast black soil region.Therefore,investigating the impacts of soil erosion on soil quality and crop yield can provide scientific basis for sustainable utilization of black soil and prevention of soil and water loss.The Binzhouhe watershed,a typical black soil region with thin soil layer in Northeast China,was chosen as the research area.Based on field investigation,in-situ observation,simulated experiment,radioisotope tracer,laboratory analysis and wavelet theoretical analysis,this study analyzed spatial distribution of soil erosion and deposition on both hillslope and watershed scales,and their impacts on soil properties and corn yield.This thesis also discussed the effects of mollic epipedon thickness and overloaded sediment deposition thickness on corn?Zea mays L.?yield and revealed the mechanisms of the impacts of soil erosion and deposition on soil quality and corn yield.The main results were as follows:?1?Spatial distribution of soil erosion and deposition at both scales of on hillslope and watershed in the thin layer black soil region were analyzed.The soil erosion/deposition rate in the watershed ranged from-4420.7 to 11988.1 t km^-2 a^-1?-means erosion and+means deposition?,with a mean of 2634.9 t km^-2 a^-1,which indicated that the watershed was dominated by soil erosion.At the watershed scale,soil erosion and deposition showed staggered distribution.Soil erosion rate of the upper stream was the largest,with a mean erotion rate of 3265.7 t km^-2 a^-1.Soil erosion rate of the middle stream ranked the second,ranged from-831.7 to 5072.1 t km^-2 a^-1,where erosion and deposition coexisted.Soil erosion/deposition also co-existed in the downstream,ranged from-4420.7 to 2823.8 t km^-2 a^-1.At the hillslope scale,severe soil erosion occurred at the middle slope position with a soil erosion rate ranged from 1255.5 to 10504.7 t km^-2 a^-1.Slight soil erosion occurred at the upper slope position with a mean soil erosion rate of 2048.3 t km^-2 a^-1.Soil deposition dominated at the lower slope position with a mean soil deposition rate of-198.9 t km^-2 a^-1 and ranged from-2720.4 to 3690.8 t km^-2 a^-1.Wavelet theoretical analysis revealed that the spatial distribution of hillslope erosion intensity showed periodic variations of 75-88 m and 144-150 m.?2?Imapcts of soil erosion and deposition on spatial distribution of soil physicochemical properties were evaluated.At the watershed scale,compared with the deposition area,the mollic epipedon thickness,organic carbon,total nitrogen,NO₃^--N and available phosphorus of the erosion area were decreased by 66.00%,27.43%,23.16%,29.01%and 53.89%,respectively,and the mean weight diameter and NH₄⁺-N of the erosion area were increased by68.82%and 19.32%.The spatial distribution characteristics of the physicochemical properties such as mollic epipedon thickness,organic carbon,total nitrogen were opposite to the spatial distribution characteristic of soil erosion rate.?3?Response relationships of spatial distributions of soil microbial properties to soil erosion and deposition were investigated.At the watershed scale,mean values of bacteria,fungi and actinomycetes quantity in the erosion area were 11.72×10⁷,4.08×10⁵ and 5.00×10⁶cfu g^-1,respectively;and the corresponding quantity in the deposition area were 14.57×10⁷,2.29×10⁵ and 6.29×10⁶ cfu g^-1,respectively.Compared with the deposition area,the bacteria and actinomycetes quantity of the erosion area were decreased by 19.6%and 20.5%,respectively,and the fungi quantity of the erosion area were increased by 44.0%.The mean contents of soil microbial biomass carbon and microbial biomass nitrogen in the erosion area were 131.4 and 1.5 mg kg^-1,respectively;and the corresponding contents in the deposition area were 207.5 and 2.5 mg kg^-1,respectively.Compared with the deposition area,contents of soil microbial biomass carbon and microbial biomass nitrogen in the erosion area were decreased by 36.7%and 38.4%,respectively.The mean value of soil microbial respiration rate was 99.8 ml kg^-1 in the erosion area;and the corresponding mean value was 190.3 ml kg^-1in the deposition area.Compared with the deposition area,the mean value of soil microbial respiration rate was decreased by 47.6%in the erosion area.At the hillslope scale,compared with the down slope position,contents of soil microbial biomass carbon and microbial biomass nitrogen at the middle slope position with the largest erotion rate were decreased by22.8%and 23.6%,respectiely.Soil microbial properties exhibited significant relationships with physicochemical properties in the watershed.Spatial distribution of soil microbial properties was affected by soil erosion and deposition characteristics through the changes of soil physical properties and redistribution of soil nutrients.?4?Responses of soil quality to soil erosion and deposition in the watershed were revealed.Mollic epipedon thickness,mean weight diameter,organic carbon,total nitrogen,microbial biomass carbon and microbial respiration rate were selected as the minimum data set?MDS?indices for soil quality evaluation.Results of soil quality evaluation showed that average value of soil quality index?SQI?in the watershed was 0.292,which indicated a low soil quality grade in the research watershed.At the watershed scale,average values of SQI were 0.510 and 0.241 in the deposition and erosion areas,respectively.Compared with the deposition area,the SQI in the erosion area was decreased by 52.8%.At the hillslope scale,soil quality was negatively related to soil erosion rate.The SQI at the middle slope position with severe erosion was 0.149,and at the down slope position with slight erosion was 0.299.Compared with the down slope position,the SQI at the middle slope position was decreased by 50.2%.The spatial distribution characteristic of the soil quality was opposite to the spatial distribution characteristic of soil erosion rate.?5?Impacts of mollic epipedon thickness and overloaded sediment deposition on corn yield were studied.Corn yield decreased as mollic epipedon thickness decreased.The minimum mollic epipedon thickness for maintaining corn yield was 20 cm.Corn yield dramatically decreased if the mollic epipedon thickness was less than 20 cm.Compared with that of the control treatment with 60 cm mollic epipedon,corn yields were decreased by 8.2%,15.8%,21.3%and 24.2%,respectively,for the treatments with 15,10,5 and 0 cm mollic epipedon.Overloaded sediment deposition showed significant negative impacts on corn yield at the corn seedling stage.Increasing the thickness of deposited layer could significantly decrease the corn yield.Compared with that of the control treatment without sediment deposition,corn yield was decreased by 31.7%when deposition thickness was 30 cm.Corn yield and mollic epipedon thickness,and corn yield and sediment deposition thickness at the corn seedingly stage were fitted and their validations showed satisfactory accuracy.?6?Influences of soil erosion and deposition on corn yield in the studied watershed were analyzed.Average value of corn yield was 6799 kg ha^-1 in the watershed.Corn yield showed extremely significant positive and negative relationships with SQI and soil erosion rate,respectively.At the watershed scale,the maximum corn yield(9007 kg ha^-1)occurred in the deposition area with good soil quality,and the minimum corn yield(5790 kg ha^-1)occurred in the erosion area with poor soil quality.Compared with the deposition area,corn yield was decreased by 35.7%in the erosion area.At the hillslope scale,corn yield at the lower slope position with better soil quality was 6884 kg ha^-1,and at the middle slope position with poor soil quality was 5315 kg ha^-1.Corn yield at the middle slope position was decreased by 22.8%,compared with the lower slope position.