Compound erosion effect of snowmelt, wind, and rainfall on sloping farmlands of Chinese typical Mollisol region

Research on the processes and mechanisms of compound soil erosion by multiple forces can provide scientific guidance for precisely controlling cropland soil erosion. Based on the seasonal alternation of freezing-thawing, snowmelt, wind, and rainfall erosion forces on sloping farmlands under natural conditions from November to next October of each year, we used a set of indoor simulation experiments of multi-force superimpositions to analyze the compound soil erosion processes of snowmelt (1 and 2 L·min-1), wind (12 m·s-1), and rainfall (100 mm·h-1). We further discussed the erosion effects of multi-force superimpositions. The results showed that, under single snowmelt erosion, an increase in snowmelt flow had a greater effect on sloping snowmelt erosion intensity than that of sloping runoff rate. When sloping snowmelt flow increased from 1 L·min-1 to 2 L·min-1, sloping runoff rate and erosion intensity increased by 2.7 and 4.0 times, respectively. Under snowmelt-wind superimposition erosion, previous sloping snowmelt erosion inhibited late wind erosion occurrence. As sloping snowmelt flow increased from 1 L·min-1 to 2 L·min-1, the inhibiting action subsequently increased and wind erosion intensity caused by previous snowmelt reduced by more than 50%. Both wind erosion and snowmelt-wind superimposed erosion intensified late rainfall erosion. The early wind erosion increased rainfall erosion by 24.5%. The snowmelt-wind superimposed effect increased the later slope rainfall erosion by 132.8% and 465.4% under 1 and 2 L·min-1 snowmelt runoff rates, respectively. The compound soil erosion amount driven by multiple force superimposition was not the sum of the corresponding erosion amount caused by single erosion force, with promoting or inhibiting effects of erosion force superimposition. The erosion effect of snowmelt-wind superposition was negative, but that of wind-rainfall superposition and snowmelt-wind-rainfall superpositions were positive.

[Paths of soil erosion controlled by typical soil and water conservation practices based on the SIMWE model: A case study of the Tongshuang watershed.]

Due to the basic topographical characteristics of the gentle and long slope lengths in the Mollisol region of Northeast China, severe soil erosion is easily aggravated by the concentration of surface flow. The spatial distribution of water depth and hydrological connectivity index were introduced to evaluate the effects of typical soil and water conservation practices on the overland flow path and hydrological connectivity based on the GIS and SIMWE (SIMulated Water Erosion) model. We analyzed the effects of different soil and water conservation practices on the hydrological connectivity, water flow path, and spatial distribution of soil erosion and sediment yield by quantifying the variations of soil infiltration rate and surface manning roughness, as well as by constructing an artificial terrain digital elevation model (DEM). The results showed that: 1) terraces could effectively affect the hydrological connectivity of the slope and regulate flow path, with significant differences between the responses of hydrological connectivity and flow path under different forms of terraced fields and ridges. The characteristics of spatial distribution of soil erosion and sediment yield varied with changes in water flow path, which would eventually lead to the intensification of local erosion; 2) practices of vegetated buffer strips and contour tillage presented limited effectiveness on runoff path controlling, though they played a significant role in sediment retention; and 3) conservation tillage could reduce the hydrological connectivity and improve the retention capacity of runoff by increasing surface roughness. This study quantified the effects of different soil and water conservation practices on the hydrological connectivity, flow path, and spatial distribution of soil erosion and sediment yield, and could provide a theoretical reference for scientific layout of soil and water conservation practices in black soil region.

[Analysis of cropping pattern in black soil region of Northeast China based on geo-information Tupu.]

Different cropping patterns have their own economic and ecological significance. Developing cropping patterns suitable for local conditions is needed to protect and make good use of black soils. At present, the cropping patterns and their spatial characteristics in the black soil region of Northeast China is poorly understood. Based on the crop classification data in 2017-2019, we used geo-information Tupu methods, distribution index model, and bivariate spatial autocorrelation to examine the cropping patterns. The results showed that: 1) The main cropping patterns in the black soil region of Northeast China were continuous maize cropping, continuous rice cropping, continuous soybean cropping, and maize-soybean rotation, accounting for 38.3%, 18.5%, 10.3% and 26.0%, respectively. The maize-soybean rotation included maize-soybean two-year rotation, maize-maize-soybean three-year rotation, and soybean-soybean-maize three-year rotation, accounting for 44.1%, 34.5% and 21.4% of the rotation area, respectively. 2) Various cropping patterns had obviously horizontal differentiation. For instance, continuous maize cropping had very obvious gradient differentiation characteristics in temperature and humidity, but soybean continuous cropping and maize-soybean rotation showed no gradient differentiation, while continuous rice cropping had gradient differentiation only in humidity. 3) Various cropping patterns had obviously spatial clustering characteristics. They had spatial transition characteristics from soybean continuous cropping, soybean-soybean-maize three-year rotation, maize-soybean two-year rotation, maize-maize-soybean three-year rotation, to continuous maize cropping. The cropping pattern in black soil region of Northeast China was dominated by continuous cropping. Understanding its distribution pattern can provide a basis for future spatial optimization of crop rotation.