The structure and functions of soil, particularly erosion resistance, are governed by aggregate stability, which fluctuates with soil temperature and moisture levels. Severe wind and water erosion across the northeast black soil region of China has prompted the widespread planting of shelterbelts to protect cultivated land. Although the shading effect of shelterbelts significantly alters soil temperature and moisture levels, most previous studies have not accounted for its effect on the soil structure. Therefore, during a single cropping season, a field experiment was conducted in this study to monitor aggregate stability in two cultivated lands near and far from shelterbelts. Through the use of partial least squares structural equation modelling (PLS–SEM), the potential factors influencing aggregate stability were determined, and possible pathways were revealed. The results indicated that, regardless of the crop type, the shading effect of shelterbelts significantly negatively influenced soil aggregate stability, which decreased by 18.82% for maize and 15.38% for soybean. Root characteristics and soil moisture were significantly negatively correlated with aggregate stability, whereas soil organic carbon and nitrogen contents and the microbial carbon-to‑nitrogen ratio were positively correlated with aggregate stability. Among these factors, soil moisture was the primary determinant, directly influencing aggregate stability (path coefficient: −0.37) and indirectly exerting a negative effect by promoting crop root growth (path coefficient: −0.27). The findings of this study advance our understanding of soil structure changes in cultivated land, thereby facilitating the development of more precise erosion models.

Grassland ecosystems, particularly in cold and high-altitude regions, are highly vulnerable to gully erosion owing to their simple structure and environmental sensitivity, making it a severe form of grassland degradation. However, most previous studies have focused on agricultural systems, leaving limited understanding of the longterm evolution and drivers of permanent gullies in grasslands. To address this issue, we analyzed gully erosion dynamics and its determinants in a 103 km2 area of the Hulunbuir grassland using remote sensing image from 1973, 1983, 2011, and 2020. Results showed that gully quantity, gully density and ground lacerative degree increased by 54.13 times, 286.66 times, and 591.01 times, respectively from 1973 to 2020, with the annual soil loss thickness of 0.023 mm. From 1973-2020, the average gully erosion rates in length, width, area, and volume were 4.64 m yr-1 , 0.06 m yr-1 , 17.17 m2 yr-1 , and 20.44 m3 yr-1 , respectively. The merge of gullies (MG) showed greater linear gully erosion rate and areal gully erosion rate than newly formed gully (NFG) and continuously developing gully (CDG), while NFG showed the highest gully widening rates. Gully erosion rates in length, area and volume peaked at 4-5 degrees slopes, with sunny and semi-sunny aspects being more conducive to development, and linearly increased with gully drainage area. Cumulative gully growth length (Delta L), area (Delta A), and volume (Delta V) increased as a power relationship of cumulative climate indicators (Pre, R, R10, R95p, RX5day, SDII, Tem) and human activity intensity (grazing intensity, built up area, road density). The coupled effects of human activity with topography and climate exert the greatest influence on gully erosion, with the relative contribution of 37.13 % and 35.75 %, respectively. Overall, during 1973-2020, permanent gullies in the Hulunbuir grassland remained in the early lifecycle stage of development. However, intensifying anthropogenic pressures coupled with amplified climate variability progressively elevated erosion risks. This trajectory necessitates implementation of scientific gully control strategies to curb accelerated soil loss and establish sustainable human-land synergies.

Gully erosion poses a significant threat to land, ecology environment and food security. However, current studies have predominantly focused on identifying the gully development and driving factors by selecting typical watersheds from broad regions, overlooking the spatial heterogeneity of gully erosion and the roles of driving factors. Therefore, to address this issue, this study aimed to investigate gully erosion and its driving factors by selecting representative small watersheds (0.48-2.93 km2) along the Mollisols Belt of Northeast China. Gully morphology, topography, soil, climate and human activity (population and land use) data were obtained by unmanned aerial vehicle, field survey and spatial analysis. The results showed that gully linear density (GLD), gully areal density (GAD) and gully number density (ND) all exhibited a trend of initial sharp decrease followed by stabilization from south to north along the Mollisols Belt. The average gully length (L), width (W), depth (D), area (A) and volume (V) in the Mollisols Belt are 130.76 m, 6.42 m, 2.27 m, 1247.19 m2, 7158.12 m3, respectively. The gully L, W, D, A, and V are centrally distributed in the range of 0-300 m, 0.5-2.5 m, 1-5 m, 0-500 m2, 0-5000 m3, accounting for 68.5 %, 75.8 %, 68.3 %, 78.5 %, 83.3 %, respectively. The frequency distribution of five parameters showed great changes along Mollisols Belt. The gully volume can be estimated by V-L power function (V=a & sdot;Lb, a=14.63-98.81, b=0.86-1.34). Gully erosion intensity reflected by GLD and GAD across all watersheds initially increased and then decreased with slope gradient and topographic wetness index (TWI), demonstrating distinct threshold behaviors, while gully erosion was more intense on sunny and semi-sunny slopes. GLD and GAD at small watershed scale were significantly and positively correlated with rainfall erosivity, mean annual precipitation, and mean annual temperature, population density, proportion of farm track area and watershed slope, while they exhibited the significantly negative correlations with MWD, soil bulk density, and soil shear strength and TWI. The topography, soil, climate and human activity factors collectively explain 83.51 % of the total variance in gully erosion, with the relative contribution of 17.8 %, 26.4 %, 27.4 %, 28.4 % respectively. These results can deepen the understanding of the characteristics and laws of gully erosion along the Mollisols Belt and provide scientific basis for the precise prevention and control of gully erosion.

The spatial heterogeneity of microbial functional genes (FGs) and the enzymes is highly correlated with nutrient cycling in soils. However, it is debated how latitude and topography influence the spatial distribution of microbial function at large scale, especially lacks reports about their interactions. To elucidate their interactive and individual effects, this study collected soil samples from the top, middle and bottom slope positions in seven locations with intervals of 80 km along the Mollisols belt in Northeast China (42 degrees 47 ' N-48 degrees 9 ' N). Shotgun sequencing and micro assay were used to characterize soil FGs and enzyme, respectively. Results indicated that (1) when slope positions were neglected, the abundance of most carbon (C) degradation FGs (starch, lignin) decreased linearly with latitude, while enzyme increased linearly. When the slope positions were considered, the variation of them with latitude was greater in middle slope than other slope positions. Phosphorus (P) FGs and enzyme activity increase linearly with latitude, and greater variation in bottom slope. Nitrogen (N) fixation FGs abundance increases firstly and then decreases with latitude in bottom slope, while increases linearly in other slope positions; (2) when latitude and slope positions were considered together, their interaction significantly influenced the distribution of C, N, and P genes and enzyme; (3) the beta diversity of FGs exhibited a unimodal pattern with latitude due to specific climate and soil heterogeneity, which differed from previous knowledge; (4) breaking previous insights, the correlation coefficient between FGs and corresponding enzyme showed quadratic function with latitude caused by microbial functional redundancy and environmental constraints, with significant positive only at 43.8 degrees-47.7 degrees. Our study highlights the interaction of slope position and latitude determined soil microbial function, and recommends sampling based on slope positions as the minimum unit. This may also enhance the accuracy of microbial function studies and C and N cycle models in Mollisols.

Gully erosion refers to the landform formed by soil and water loss through gully development, which is a critical manifestation of soil degradation. However, research on the spatio-temporal variations in erosion gullies at the county scale remains insufficient, particularly regarding changes in gully aggregation and their driving factors. This study utilized high-resolution remote sensing imagery, gully interpretation information, topographic data, meteorological records, vegetation coverage, soil texture, and land use datasets to analyze the spatio-temporal patterns and influencing factors of erosion gully evolution in Bin County, Heilongjiang Province of China, from 2012 to 2022. Kernel density evaluation (KDE) analysis was also employed to explore these dynamics. The results indicate that the gully number in Bin County has significantly increased over the past decade. Gully development involves not only headward erosion of gully heads but also lateral expansion of gully channels. Gully evolution is most pronounced in slope intervals. While gentle slopes and slope intervals host the highest density of gullies, the aspect does not significantly influence gully development. Vegetation coverage exhibits a clear threshold effect of 0.6 in inhibiting erosion gully formation. Additionally, cultivated areas contain the largest number of gullies and experience the most intense changes; gully aggregation in forested and grassland regions shows an upward trend; the central part of the black soil region has witnessed a marked decrease in gully aggregation; and meadow soil areas exhibit relatively stable spatio-temporal variations in gully distribution. These findings provide valuable data and decision-making support for soil erosion control and transformation efforts.

Soil moisture conditions and crop root growth collectively influence the turnover (breakdown-buildup) of soil aggregates during different crop growth periods. However, evaluations of these effects under actual field conditions have been limited. Therefore, aggregates of Mollisols from cultivated land (1-10 cm) were taken as the research objects. Aggregates in four size fractions (A: 5-2 mm, B: 2-0.25 mm, C: 0.25-0.053 mm, D: < 0.053 mm) were tracked using the rare earth element (REE) tracing method during soybean growth periods (I: planting, II: emergence, III: second trifoliolate, IV: fifth trifoliolate, V: full bloom, VI: full pod, VII: full seed, VIII: harvest). The key findings were as follows: i) The aggregate composition was predominantly size fraction C, which accounted for 34.53-43.41 % during the soybean growth periods. The mean weight diameter (MWD) displayed a bimodal pattern, with peaks of 0.44 and 0.41 observed in II and VI, respectively. ii) Approximately 33.13-46.16 % of the aggregates in size fractions A and B tended to break into size fraction C during soybean growth, with neighboring size fractions contributing 18.62-48.60 % to the aggregate formation process. The turnover rate (TR) of size fraction D was the highest. iii) Soil moisture conditions were significantly correlated with the TR of each size fraction during the growth periods (P < 0.05). iv) The root morphological characteristics of the < 2 mm aggregates were significantly negatively correlated with the TRs of size fractions B and C in V, but positively correlated with the TRs of size fractions B, C and D in VI. The study reveals significant variations in aggregate turnover patterns across different growth stages, providing valuable insights into the evolution of soil structural properties in cultivated lands.

Gully is the most visible sign of land degradation, but its effects on runoff and sediment dynamics during snowmelt conditions remain poorly understood. This study monitored a typical gully in the Mollisols region of Northeast China to investigate runoff and sediment transport at the Gully Head (GH) and Gully Tail (GT) during spring snowmelt. Results showed that gully significantly influenced snow distribution, with deeper snow accumulation than on slopes. Runoff at the GH lasted 9 days, while gully connectivity extended catchment runoff by 10 additional days. Runoff temporal variation at GH and GT was broadly consistent, with GH contributing 7.4% of the total runoff at GT. Peak runoff discharge and sediment concentration occurred on the sixth day after snowmelt onset, driven by snow cover and air temperature. Gully significantly increased the sediment concentration from the upslope runoff. Runoff responses to temperature varied by melt stage, with GT showing higher sensitivity, especially under high-runoff conditions. High sediment yield was linked not to snow depth, but to late-stage snowmelt and soil thawing, when erosion sensitivity peaked. Hysteresis analysis revealed dominant clockwise loops during this phase, contrasting with figure-eight and counterclockwise patterns in other stages. These findings highlight the importance of targeting erosion control during late snowmelt when runoff intensifies and soils thaw.

In Northeast China, straw residues are integrated into fields to improve the soil structure and fertility after the autumn harvest. However, the optimal amount of straw addition is unclear. To determine whether an increase in straw addition is correlated with an increase in soil aggregate stability, the study focused on black cropland soil and was conducted through field incubation experiment (lasting 150 days) during seasonal freeze-thaw periods, implemented six different straw treatments: CK (0%), SA1 (1%, i.e., 10 g of straw per kg of soil), SA3 (3%), SA5 (5%), SA7 (7%), and SA9 (9%). The results revealed that under freeze-thaw conditions, aggregate stability significantly increased only when the straw addition amount was >= 5%. At this straw addition level, straw residues enhanced aggregate stability in two ways. First, the straw decomposition significantly increased SOC content, which serves as a binding substance for aggregates and promotes the formation of aggregates > 0.25 mm. Second, straw particles combined with soil particles to form straw-soil composite macro-aggregates that exhibited high water stability. However, aggregate stability was not positively correlated with the straw addition amount. This was because 5% straw addition was sufficient for the soil to reach carbon saturation, and the SOC content showed no significant change with further increasing straw addition. Moreover, excessive straw addition not only led to nitrogen limitation and slowed down the straw decomposition rate but also wasted straw resources. Therefore, 5% straw addition is optimal for improving soil aggregate stability. These findings provide a theoretical basis for how to improve the soil structure and fertility through the rational design of autumn straw return measures, thereby improving soil conditions for spring sowing and seedling emergence in Northeast China.

Rainfall is the main external force affecting soil surface structure. Many studies have evaluated the impact of a single rainfall event. However, the superimposed effects of multiple rainfall events on soil structure remain unclear. Therefore, surface soil from tillage in the black soil region of Northeast China was selected as the research object, and simulated rainfall and CT tests were combined to characterize the 3D indices of surface soil aggregates and pores under multiple rainfall events, uncovering the dynamic changes in the soil surface structure. The results showed that during rainfall, only a dense layer is formed on the upslope, while an alternating superposition of sedimentary-dense layer multilayers occurs on the downslope. For the upslope, as the rainfall frequency increased, the percentages of 0.25-0.053 mm aggregates in the dense layer with rainfall intensities of 40 mm/h and 70 mm/h exhibited opposite trends, with ranges ranging from 6.29 to 12.16 % and 45.21 to 70.71 %, respectively. For the downslope, when the sedimentary layer is at the top, the percentage of 0.25-0.053 mm aggregates decreases with increasing rainfall frequency, but the percentage of 0.25-0.053 mm aggregates increases when there is a dense layer on top of the sedimentary layer. In summary, the uppermost sedimentary layer at the downslope mainly shows fragmentation, while the lower sedimentary layer shows aggregation. The pore structure of the sedimentary layer downslope is influenced mainly by the fragmentation of its own large aggregates, whereas the pore structure of the dense layer is influenced mainly by the vertical downwards transport of the small aggregates of the upper layer of the sedimentary layer. The results of this study are beneficial for revealing the erosion of black soil slopes and the evolution of soil structure.

[Objective]To investigate the impact of intermittent rainfall on the amount and sorting characteristics of black soil splash erosion.[Methods]This study is based on artificial simulated rainfall experiments,with two rainfall intensities(40,70 mm/h)designed,each with 5 rainfall events,to analyze the splashing erosion amount and particle size distribution characteristics of black soil under different rainfall conditions.[Results]Under two different rainfall intensities,there is a dynamic development process of alternating strength between"no crust weak crust strong crust weak crust new crust"in the soil surface layer of different rainfall sites.Under two different rainfall intensities,the maximum values of splashed aggregate MWD and GMD appeared in the fourth rainfall,and the minimum values appeared in the first rainfall.The agglomerates with a particle size of 5～2 mm did not migrate in each rainfall,and the splashed agglomerates were mainly composed of particles with a size of 2～0.25 mm,accounting for 36.49％～58.61％and 49.1 0％60.09％of the splashed erosion amounts of the two rainfall intensities,respectively.The erosion amount of the five rainfall events showed a trend of first increasing and then decreasing with the decrease of particle size,while the mass percentage with particle size＜0.053 mm showed a trend of first decreasing and then increasing with the increase of intermittent frequency.The mass percentage with particle size＜0.053 mm all showed the minimum value in the third rainfall event,which was 18.21％and 17.63％,respectively.[Conclusion]Rainfall can lead to the formation of soil crust,and the thickness of soil crust shows dynamic changes with the increase of rainfall frequency.In the third rainfall,the soil crust thickness is the highest,and at this time,the splash erosion amount has the minimum value,mainly greater than 0.053 mm.The research results provide reference for the study of soil water erosion mechanism in the black soil area of Northeast China.

During freeze-thaw cycling, aggregates undergo a dynamic change in breakdown-formation (turnover), however, how the turnover occurs between aggregates of various particle sizes is not clear. To clarify the influence of freeze-thaw cycling on the dynamic changes in the particle size of soil aggregates, soil aggregates from the Black Soil Region of Northeast China were selected as the research objects. The study conducted in situ dynamic monitoring experiments, innovatively applying the rare earth oxide (REO) tracer method to natural conditions of freeze-thaw cycles (autumn freeze-thaw period, freezing period, and spring freeze-thaw period), accurately tracking the turnover paths and quantifying the turnover rates between aggregates of various particle sizes. The results revealed that the total value of the formation paths of the 2-5 mm aggregates and 0.25-2 mm aggregates increased during the autumn freeze-thaw period. The number of freeze-thaw cycles and accumulated snowfall were significantly positively correlated with aggregate stability, with an increase in the number of freeze-thaw cycles and accumulated snowfall resulting in an increase in the proportion of aggregates > 0.25 mm, which improved aggregate stability. In addition, the total value of the breakdown path of macro-aggregates increased during the spring freeze-thaw cycling period. Soil moisture was significantly negatively correlated with aggregate stability, with increased soil moisture resulting in a decrease in the percentage of aggregates > 0.25 mm, which resulted in a decrease in aggregate stability. The study can provide a reference understanding for the effects of freeze-thaw cycles on the structure of black soil and provide a theoretical basis for improving the quality of arable land.

In seasonal frozen soil, freezing and thawing can change the physical and mechanical properties and affect slope stability. There are complex moisture conditions in the main water transfer canal. A study of the hydrothermal evolution of canals with different initial water contents under the action of freezing and thawing is of great importance for the prevention and control of canal slope slides. Hydrothermal coupling models are the key to revealing the canal's hydrothermal evolution. As some of the modeling parameters in the current hydrothermal coupling model are based on empirical values, particularly those in the van Genuchten equation, which are not necessarily related to soil properties, they are not suitable for analyzing the hydrothermal evolution of canals. This paper determines the soil-water characteristic curve from the cumulative curve of particle gradation in the subsoil, and then determines the hydraulic parameters of the subsoil using the VG model, which then corrects the hydrothermal coupling model. The method of modifying the hydrothermal coupling model is original, which makes the model more realistically reflect drainage soil characteristics. During freezing and thawing of channel slopes with different initial water contents (21%, 25%, 29%, 33%, 37%, and 41%), temperature field, water field, and ice content distributions were investigated. Using the V-G model, the optimal parameters for canal subsoil were a = 0.06, n = 1.2, and m = 0.17, and temperature distribution trends between canals with different water contents were basically similar. Water will accumulate at the bottom as the liquid water content increases at the canal boundary.

Understanding the spatial distribution of soil organic carbon (SOC) and soil nutrients is crucial for optimizing land management in watersheds. This study explored the spatial distribution of SOC, total nitrogen (TN) and total phosphorus (TP) in topsoil (0-20cm) at a hilly small watershed site in Northeast China, and identified the controlling factors. The Gaussian mixture model optimally described SOC and TN with the ratio of nugget to sill variance (C-0/[C+C-0]) indicating moderate spatial dependence for SOC (63.7%) and TN (59.3%). TP was best modelled by the spherical model and demonstrated weak spatial autocorrelation and strong human influence, with a nugget to sill variance of 0.841. Land use significantly affected SOC, TN and TP contents, with the highest values recorded in woodland, followed by farmland and shrubland. Soil properties including bulk density (BD), gravel content (GC), moisture content (MC), soil porosity (SP) and the mean weight diameter (MWD) of water-stable aggregates significantly correlated with SOC and TN content, but not with TP. Redundancy analysis revealed that soil properties (BD, GC and SP), topography (slope and aspect) and gully erosion contributed 55.7%, 24.7% and 4.3% of the spatial variation in SOC, TN and TP, respectively. Hence, these are the dominant factors shaping the spatial variation of SOC and soil nutrients at the site. These results can aid the further development of optimized land management strategies.

Gully erosion is one of the most severe types of land degradation, hindering food production and sustainable agricultural development. However, the historical evolution process and the impact of land use change on gully erosion remain unclear. To address this issue, we conducted a field investigation on gully erosion in 2018 and interpreted land use and gullies using historical remote sensing images in 1968 and 1978 over an area of 84.48 km(2). The study found that from 1968 to 1978 to 2018, all gully morphological parameters including gully length density and gully areal density increased significantly. The main origin of gully erosion found was from dry farmland. The annual soil loss rate induced by gully erosion was 1.46 mm during 1968-2018. Gully erosion rates were higher during 1968-1978 than during 1978-2018. Furthermore, the length, areal and volumetric erosion rates in gullies formed by multiple gullies merging was greater than that of newly formed gullies (NFG) and gullies developing continuously from a single pre-existing gully, while the widening rate of NFG was highest. The susceptibility of land use types to gully erosion was in the order of woodland < dry farmland < degraded land. The annual average increase in gully area was 871.09 m(2) km(-2) year(-1) for parcels that were converted from woodland to dry farmland, which was 5.56 times and 1.78 times greater than that of woodland and dry farmland maintenance, respectively. Therefore, urgent implementation of ecological land use plans and gully erosion control practices is suggested for this region. (c) 2023 International Research and Training Center on Erosion and Sedimentation, China Water and Power Press, and China Institute of Water Resources and Hydropower Research. Publishing services by Elsevier B.V. on behalf of KeAi Communications Co. Ltd. This is an open access article under the CC BYNC -ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

The decomposition of maize residues has a vital influence on soil aggregate buildup–breakdown (turnover) processes, but the following remain unclear: i) which size aggregates of Mollisols are primarily affected by the decomposition of maize residues and ii) the turnover proportions of these aggregates. In the study, rare earth oxides (REOs) were used to trace and quantify the buildup–breakdown paths of soil aggregate fractions during the whole incubation time. The two treatments were designed as follows: i) REO-labelled soil with maize residues addition (maize residue treatment) and ii) REO-labelled soil without maize residues addition (control, CK). The soil respiration, aggregate size distribution, REO concentrations, SOC and pH were measured during 84 days of incubation. The results showed that on days 0–14, the incorporation of maize residues significantly increased soil respiration and promoted the formation of 2–5 mm and 0.25–2 mm aggregate fractions at the expense of <0.25 mm aggregates. On days 14–84, the addition of maize residues continued to promote the formation proportions of the 2–5 mm aggregate fractions and reduced the breakdown proportions of the 0.25–2 mm aggregate fractions. At the end of incubation, the proportions of 0.25–2 mm, 0.053–0.25 mm, and <0.053 mm aggregates that formed into 2–5 mm aggregates were 5.1 %, 5.7 %, and 6.4 %, respectively, in the maize residue treatment, and the proportions of 0.25–2 mm aggregates that broken into 0.053–0.25 mm and <0.053 mm aggregates decreased by 23.2 % compared to those in the CK treatment. The larger the aggregate size was, the greater the buildup rate in the maize residue treatment. The buildup rate of the 2–5 mm aggregate fractions in the maize residue treatment was the largest and increased with increasing incubation time, reaching 529.3 % at the end of incubation. The 2–5 mm, 0.053–0.25 and <0.053 mm aggregate fractions mainly transferred (buildup or breakdown) to the 0.25–2 mm aggregate fractions. The addition of maize residues significantly increased organic matter contents during the whole incubation time, increased the soil pH on days 0–42. This study provides a reference for the impact of maize residues on Mollisols soil structure.

Soil aggregate stability and erodibility reflect soil resistance to erosion. Although the factors influencing soil aggregate stability and erodibility have been extensively studied, the driving effects of these factors and their interactions remain limited. 184 sampling sites were selected in topsoil (0-20 cm) of a small watershed (1.42 km(2)) in a Mollisol watershed to measure soil bulk density (BD), soil porosity (SP), soil moisture content (MC), soil organic carbon (SOC), total nitrogen (TN), >0.25 mm water stable aggregates content (WSA(> 0.25)), mean weight diameter (MWD) and K factor. Pearson correlation analysis, semi-variance function, redundancy analysis (RDA), and structural equation model (SEM) were used to quantify the impact of environmental variables (individual and interaction) on the spatial variations of WSA(> 0.25), MWD, and K factor. The findings indicated that higher values of WSA(> 0.25) and MWD are observed in the central and western watershed, while the K values tend to be lower in areas with high WSA(> 0.25) and MWD values within the watershed. The Exponential model optimally described WSA(> 0.25), MWD, and K factor with C-0/(C + C-0) indicating moderate spatial dependence for MWD (39.79 %) and K factor (42.86 %), while strong spatial autocorrelation for WSA(> 0.25) (7.23 %). Soil properties (moisture content, silt content, and bulk density), topography (elevation, SPI, and slope), and land use contributed 46.6 %, 41.4 %, and 9.1 % of the spatial variation in WSA(> 0.25), MWD, and K factor, respectively. SEM revealed that silt content, SOC, and water condition played a fundamental role in controlling the spatial variability of WSA(> 0.25), MWD, and K factor. Topography exerted both direct or indirect effects by coupling land use or soil properties spatially. Land use had direct or indirect effects on WSA(> 0.25) and K factor through regulating MC, but it primarily influences MWD indirectly through impacting MC. These results could clarify the roles and influencing paths of factors controlling the spatial heterogeneity of WSA(> 0.25), MWD, and K factor, contributing to optimizing land management strategies.

Clarifying the responses of runoff and soil erosion to crop type and rainfall regime is important for the optimization of crop planting systems and land use and management. This study was conducted to quantify the effects of five grain-forage crop types and rainfall regimes on sloped runoff generation and soil loss, and to further identify the factors influencing runoff and soil erosion in Mollisols region of Northeast China. Runoff and soil loss were monitored from 24 runoff plots including wheat, corn, soybean, alfalfa, and bromegrass, with the bare land as a control. 31 erosive rainfall events were classified into three rainfall regimes: regime I with low precipitation (P) and duration (D), moderate intensity (I30) and frequent occurrence; regime II with moderate P, long D and low I30; and regime III with high P and I30, moderate D and less frequent occurrence. Soil loss caused by regime III was 3.61-12.93 times greater than that under regimes I and II. Five crops reduced runoff and soil loss by 21.5%-69.3% and 54.1%-77.0%, respectively, of which bromegrass showed the highest reduction, especially the reductions of alfalfa and bromegrass under regime III, which were significantly higher than those of the three grain crops. Wheat showed a higher runoff reduction than soybean and corn but its soil loss reduction was lower due to harvest in mid-July. Crop type greatly influenced the correlations between runoff and soil erosion and rainfall and plant properties. Changes in runoff were significantly related to P, rainfall erosivity (EI30), coverage, plant height and root density, and the variations in soil erosion were dominated by runoff depth, D, EI30, and coverage. Path analysis showed that the rainfall and runoff properties produced larger influences on runoff depth and soil loss rate than plant traits. More attention should be paid to rainfall regime III, and grain and forage crops with shorter stems and higher coverage and earnings are preferred.

[Objective] The soil nutrient characteristics and influencing factors of surface soil gully erosion for low hilly terrain in the black soil area were studied in order to provide data and theoretical support for the rational use of land resources, accurate management of soil fertility, and restoration of degraded soil in the black soil area. [Methods] Surface soil gully erosion for different types of eroded ditches in Yanshou County, Heilongjiang Province was determined by measuring and analyzing soil samples from the 0—40 cm layer in each part of the erosion gully. [Results] ① The contents of soil organic matter, total nitrogen, total phosphorus, total potassium, available phosphorus, available potassium, and alkali hydrolyzable nitrogen were significantly different (p<0.05) for different erosion gully types compared with the check treatment. As an erosion gully developed, soil organic matter decreased in the 0—40 cm layer, and the contents of total nitrogen, total phosphorus, total potassium, available phosphorus, available potassium, and alkali hydrolyzable nitrogen also decreased. These nutrient contents were significantly different (p<0.05) in different soil layers. Soil nutrient contents decreased with increasing depth. Because of erosion deposition, the contents of soil organic matter, total nitrogen, total potassium, and alkali hydrolyzable nitrogen decreased dramatically at the head of the gully, and at the same time, the contents of soil organic matter, available phosphorus, and available potassium decreased slowly. ② The soil degradation index followed the order of CK>A2>A1>A3 in the 0—40 cm layer as erosion gullies developed, and the soil was gradually degraded. [Conclusion] Soil nutrients had an overall significant negative correlation with bulk density, and soil nutrients were positively correlated with water stable aggregates and clay content. Soil profile differences were the fundamental reason for the variation in soil nutrients. Erosion gully development was the secondary reason for nutrient changes. The contents of soil organic matter, total nitrogen, and total potassium were also affected by positional differences.

[Objective] The effects of erosion on the surface soil of erosion gullies in sloping cropland soils in a black soil area were studied in order to provide theoretical support for the rational utilization of soil resources and regional soil and water conservation work in black soil areas. [Methods] The study was conducted on erosion gullies with different degrees of development in Yanshou County, Harbin City, Heilongjiang Provicne. Particle size distribution and water storage properties of soil on the slope, at the bottom of the gullies and at the head of the gullies were quantitatively described. [Results] ① Soil bulk density, maximum water-storage capacity, maximum water-retention capacity, total storage capacity, dead storage capacity, and maximum effective storage capacity at different depths were significantly different (p<0.05). As soil depth increased, soil bulk density also increased, and water-storage, water-retention, and effective water storage capacity decreased. Each layer had a maximum water-storage capacity of about 90% of its saturated capacity, and the effective water utilization rates were 44.79% and 41.87%, respectively. The development of erosion gullies had a clear influence on effective soil water. ② The infiltration characteristics generally showed that the initial infiltration rate>the 30-minute infiltration rate>the stable infiltration rate. As soil depth increased, the infiltration characteristics of the three indicators decreased between gully A2 and A4 for different erosion degree gullies. In the 20—40 cm layer, the infiltration characteristics of gully A1 to A4 followed the order of CK (control group)> gully A1> gully A4> gully A2> gully A3. Infiltration initially declined and then increased. With the development of the erosion gully, soil infiltration decreased and then increased. ③ The development of erosion gullies was the main reason for the change in clay content. The percentage of clay in the 0—40 cm layer tended to increase first and then decrease. The percentage of sand in the 0—20 cm layer tended to decrease first and then increase, showing a trend toward increased coarseness. ④ The soil degradation index followed the order of gully A1> gully A2> gully A3> gully A4 in the 0—20 cm layer. Soil degradation increased with the development of erosion gullies. Soil degradation was most severe in gully A4. [Conclusion] The differences in soil profiles was the main reason for the differences in physical properties of black soil. Soil water-holding capacity in the 0—20 cm layer was weakened and soil degradation became severe as erosion gullies developed.

为了解黑土坡耕地侵蚀沟融雪径流特征及水质情况,选取黑土农田坡面及典型侵蚀沟,采用野外实地观测及实验室分析的方法,测定分析了坡耕地融雪期径流量及氮磷含量.结果表明:2021 年春季,研究区融雪径流发生在3月中旬,主要融雪期共5 d;融雪径流平均流速1.14 L/s,融雪期日平均流量呈先增加后减小的趋势,与日最高气温变化具有较好的一致性;融雪径流中硝态氮、总氮、总磷平均质量浓度分别为 5.03 mg/L、9.06 mg/L、0.57 mg/L.融雪径流会造成坡耕地氮磷养分的流失,进而汇入下游河流成为水质污染源之一.融雪径流可造成坡耕地氮磷养分的流失,土壤有机质含量降低,耕地质量退化,影响粮食产能.加强黑土坡耕地融雪侵蚀研究对于黑土地治理保护具有重要意义.