Tillage Erosion And Its Relationship With Spatial Patterns Of Soil Organic Carbon, Nitrogen And Phosphorus In Black Soil Region

Massive research on soil erosion so far in northeastern China has focused on quantifying the rates and patterns of water erosion.Soil transportation caused by farming equipment,or tillage erosion,however,has largely been overlooked as a significant geomorphic process in the black soil region.Tillage erosion has been globally identified as soil degradation process affecting soil productivity,landscape evolution and carbon cycling.Understanding the patterns and processes involved in soil redistribution across agricultural landscapes is crucial to control soil erosion and assess the impact of erosion on soil quantity.The objectives of this study,therefore,were to 1)qualify tillage erosion rates due to moldboard plowing using small-stone tracing method;2)to investigate the spatial distribution of tillage and water erosion in a typical sloping cultivated land;3)to explore the response of soil organic carbon?SOC?and its fractions to different driving forces of erosion?tillage and water?;4)to elucidate the variations in soil total nitrogen?TN?and total phosphorus?TP?induced by tillage and water erosion based on the method of geostatistics.The results showed that moldboard plow operation moved great quantities of soils resulting to potential erosive.After a single tillage pass,traced soils were translocated 10–34cm at 32.68–134.14 kg·m^-1,with more soil materials translocated in the downslope direction than in the upslope direction.The tillage erosivity,expressed in terms of tillage transport coefficient,was 234 kg·m^-1 tillage pass^-1.A linear regression equation was developed expressing mean soil flux and translocation percentiles as a function of slope gradient,indicating tillage translocation is significantly affected by slope gradient,especially for upslope tillage.The slope gradient of cultivated lands in black soil area is generally smaller,but the tillage erosion could be serious because of higher tillage depth and higher speed of equipment operations.Tillage erosion and deposition rates changed according to the slope positions,decreasing in the order:upper-slope>lower-slope>middle-slope>toe-slope and toe-slope>lower-slope>middle-slope>upper-slope,respectively;while the order of water erosion rates decreased in the order:lower-slope>toe-slope>middle-slope>upper-slope.Tillage and water erosion cooperatively triggered intense soil loss in the lower-slope areas,where characterized by a convex shape with large slope gradient,and caused soil accumulation in the toe-slope areas.The correlation analyses for total slope showed that tillage erosion was significantly correlated with SOC and POC,while there were a lack of correlations between water erosion and total SOC or its fractions;indicating that the influence of tillage erosion on C cycling is severer although the rate of water erosion(5.96¹01.17 t·h^-1·a^-1)is orders of magnitude bigger than tillage erosion(0.02⁷.02 t·h^-1·a^-1)in black soil area.However,correlation analyses for different slope positions indicated that water erosion plays a major role in controlling C cycling at a typical slope position?lower slope?.The SOC?POC and DOC concentrations in depositional areas were higher than erosional areas,however,MBC showed an opposite trend.Additionally,tillage dominated dynamic of SOC by depleting POC.Under the different effects of erosion process?tillage and water erosion?,TN and TP contents exhibited a similar spatial pattern in the study field:they increased from upper slope to middle slope position and then decreased in lower slope position.The correlation analyses for whole slope showed that there were a lack of correlations between tillage/water erosion and TN/TP contents,while the TP was significantly correlated with water erosion rates in the upper and lower slope position,indicating that water erosion results in TP loss in this position.However,TN was uncorrelated with tillage or water erosion in any slope positions.Results from this research indicates that erosion is one of the main factors leading to variations in soil nutrients on sloping farm land,and water erosion plays greater role in TP loss.