Slope Farmland Research Articles

Study on soil hydraulic properties of slope farmlands with different degrees of erosion degradation in a typical black soil region.

In order to explore the impact of soil erosion degradation on soil hydraulic properties of slope farmland in a typical black soil region, typical black soils with three degrees of erosion degradation (light, moderate and heavy) were selected as the research objects. The saturated hydraulic conductivity, water holding capacity and water supply capacity of the soils were analyzed, as well as their correlations with soil physicochemical properties. The results showed that the saturated hydraulic conductivity of black soils in slope farmlands decreased with erosion degradation degree, which was higher in 0-10 cm soil layer than in 10-20 cm soil layer. The water holding capacity and water supplying capacity of typical black soils also decreased with the increase of erosion degradation degree, and both of them were stronger in the upper soil than in the lower soil. With the aggravation of erosion degradation of black soils, soil organic matter content decreased while soil bulk density increased, leading to the decline of soil hydraulic conductivity. The increase of soil bulk density and the decrease of contents of organic matter and >0.25 mm water stable aggregates were the main factors leading to the decrease of soil water holding capacity. These findings provide scientific basis and basic data for rational utilization of soil water, improvement of land productivity and prevention of soil erosion.

A dataset of carbon and water fluxes in the sample plots of natural regeneration at Puding Station of Guizhou Province (2015–2019)

Targeting the Shawan natural regeneration ecosystem (converted from farmland in 2010) in Puding County, we adopted the eddy covariance (EC) system to carry out long-term positioning observations of carbon and water fluxes during the natural regeneration of ecosystems after farmland conversion in karst areas. Puding Station belongs to the National Field Scientific Observation and Research Network and the China Ecosystem Research Network. Based on the data processing requirements of the ChinaFLUX, we compiled in this dataset the carbon and water fluxes as well as conventional meteorological data in Shawan from 2015 to 2019, including net ecosystem carbon exchange (NEE), ecosystem respiration (Re), gross primary productivity (GPP), latent heat flux (LE), sensible heat flux (H), air temperature, air relative humidity, wind speed, wind direction, total solar radiation, net radiation, precipitation and so on. This dataset can provide observational evidence for the study of the carbon sink capacity and water consumption characteristics of the ecosystem at the early stage of natural regeneration after the conversion of sloping farmland to forest in karst areas in southern China, as well as their response to climate change.

Characterization of Two Main Forest Cover Loss Transitions in North Korea from 1990 to 2020

This study aims to characterize forest cover transitions in North Korea and identify deforested areas that are degraded or at risk of degradation. We used phenological information and random forest classifiers to perform a deforestation classification. We then extracted the two main forest cover loss patterns, sloping farmland (farmland with slope greater than 6 degrees) and unstocked forest (crown cover less than 20%), for the years of 2000, 2010, and 2020. Based on the deforestation map of each year, we analyzed the deforestation dynamics from 1990 to 2020. Forests showed decreases in cover by 27% over the 30-year study period and accounted for 41.5% of the total land area in 2020. Deforestation spread into the core area, which led to severe shrinkage and fragmentation of forests. Unstocked forest and sloping farmland experienced the highest rates of loss among the forestland uses and accounted for 48.9% and 39.3% of the total loss over the study period, respectively. During the study period, 25,128 km2, 5346 km2, and 6728 km2 of forestland was cleared, degraded, and was at risk of degradation or barrenness by artificial repeated fires, respectively. This methodological framework provides a valuable template for areas that are difficult to access, and the deforestation dynamics results can provide a basis for conservation and sustainable management of forest resources.

Contribution of soil aggregate particle size to organic carbon and the effect of land use on its distribution in a typical small watershed on Loess Plateau, China

Soil organic carbon (SOC) is an important pool in the global carbon cycle, playing a vital role in moderating atmospheric CO2 concentrations. Soil is the largest carbon pool in terrestrial ecosystems and, as the basic unit of soil structure, soil aggregates are key to protecting soil carbon pools. However, the influence of soil aggregate particle size, SOC distribution, and the contribution of different particle sizes to SOC is still unclear, particularly under different land use types. In this study, soil samples were collected from five land use types (slope farmland (SF), forest (FL), grassland (GL), shrubland (SL), and terraced field (TF)) in a typical small watershed in the Loess Plateau, China. We analyzed the soil aggregate particle size, composition, and stability after dry and wet sieving, SOC content of different particle sizes in aggregates, and the effects of different aggregate particle sizes and land use on the distribution of SOC. The results showed that, the surface soil (0 ∼ 20 cm) water-stable aggregates were relatively stable, particularly under FL, the mean weight diameter (MWD) value was 2.16 mm. Deep soil (40 ∼ 60 cm) non-water stable aggregates were more stable, and GL was optimal, the MWD value was 3.94 mm. SOC and total nitrogen (TN) were significantly correlated with water-stable aggregate stability indicators (p < 0.01). The SOC content in the small aggregates (0.25 ∼ 2 mm) was the highest and lowest in the microaggregates (<0.25 mm) under different land use. The carbon/nitrogen (C/N) ratio of microaggregates was significantly higher in SF (the C/N ratio was 23.17) and GL (the C/N ratio was 31.04) than in other land uses (p < 0.01) in the 20–40 cm soil layer. In surface soil, small aggregates contributed>50% to SOC in SF and TF. In deep soil, small aggregates under all five land uses made the largest contribution rate to SOC at 57%. These findings indicate that carbon sequestration in the study area can be improved by a combination of appropriate soil management with ecological construction to increase the content of small aggregates, strengthen the fixation and protection of SOC, and reduce carbon emissions in the soil.

Effect of Terracing on Soil Moisture of Slope Farmland in Northeast China’s Black Soil Region

The impact of terracing construction on the soil moisture content of slope farmland was analyzed at three sites in northeast China’s black soil region, across a range of latitudes and hydrological, temperature and soil quality conditions. At each research site, slope farmland with terracing was compared to unterraced slope farmland with a similar shape and gradient. During the wet crop growth period (July) and dry postharvest period (October) of 2022, the TRIME-PICO64TDR soil moisture measuring instrument was used to measure the soil moisture content at depths of 0–60 cm. Terracing increased soil moisture content by up to 2.83 percentage points during the crop growth period and by up to 1.69 percentage points during the postharvest period. Terracing had a significant impact on the volumetric soil moisture content of the shallower soil layer (0–30 cm) during the growing period, and on the volumetric soil moisture content of the deeper soil layer (30–60 cm) during the postharvest period. Terracing weakens the effect of slope position on volumetric soil moisture, reducing differences in volumetric soil moisture content among different slope positions. The difference in the water conservation benefit of terracing among the sites is mainly related to soil quality: the lower the soil bulk density and the higher the silt clay content is, the greater the benefit of terracing for retaining moisture. The findings of this study can be beneficial for guiding management measures for slope arable soil in black soil regions around the world.

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.

Characteristics of the Sediment Transport Process in Vegetation Hillslopes under Different Flow Rates

Vegetation filter strips (VFSs) have always been an important measure to control agricultural soil erosion, especially in mountainous and hilly areas with more sloping farmland. To investigate the mechanism of the sediment-trapping process by VFSs, a series of tests were conducted with four gradients of flow rate, 7.5–45 L min−1 m−1, and two different sediment concentrations of 40 and 120 g L−1. The whole process of overland flow was monitored, and sediment and particle size samples from the inflow and outflow were collected and measured. The results showed that the changes in sediment concentration did not significantly affect the corresponding coefficients in the power function relationship between overland flow rate and velocity. Using the Reynolds number alone cannot effectively indicate the flow pattern of overland flow on vegetation hillslopes. The peak particle size and linear function were effective in describing the relationship between sediment particle composition and delivery rate during the sediment-trapping process by VFSs. During the sediment-trapping process, the sediment-trapping capacity of VFSs continued to decrease. The increase in sediment discharge was accompanied by a higher proportion of coarse particles. Under the same flow rate conditions, when the sediment concentration was higher, the coarse particles and their proportion also increased faster. Therefore, using only a certain particle size threshold to distinguish suspended and transported sediment may lead to inaccurate estimation of the sediment-trapping performance of VFSs. This study deepened the understanding of the mechanism of water–sediment processes on vegetation hillslopes and promoted the widespread and efficient application of VFSs management technology.

Composite Factors during Snowmelt Erosion of Farmland in Black Soil Region of Northeast China: Temperature, Snowmelt Runoff, Thaw Depths and Contour Ridge Culture

Snowmelt erosion could cause serious damage to soil quality and agricultural production conditions of slope farmland in the black soil region of northeast China. Contour ridge tillage is a traditional and effective measure to mitigate soil loss on slope farmland. However, the characteristics and influence factors of snowmelt erosion of slope farmland with contour ridge culture and the effect of this measure on the snowmelt process have not been comprehensively investigated, especially at the field scale. To bridge the gap, in situ observation was conducted on the snowmelt erosion process of a typical farmland in Baiquan County, Heilongjiang Province, China. The results revealed that during the snowmelt erosion period, the average daily snowmelt runoff volume and sediment concentration exhibited a trend of first increase and then a subsequent decrease. In the early stage, although the sediment concentration was large, limited discharge and soil thaw depths led to minimal soil loss. In the following stage, due to increased runoff and thaw depths, 94% of the total soil loss amount was obtained with an obvious erosion path formed. For each event, when soil thaw depths were shallow, sediment concentration had a high and early peak, whereas a reverse trend was observed when thaw depths increased. The hysteresis relationship of discharge–sediment indicated that the location where snowmelt erosion primarily occurred would change, under the influence of variations in runoff, freeze and thaw action, thaw depths, and micro-topography. The results could provide a guide in the control of soil erosion in seasonal snowmelt-erosion-prone areas.

Hydrus-3D-Based Study on Water Retention in Chinese Sloping Farmland

Hydrus-3D-Based Study on Water Retention in Chinese Sloping Farmland

Biochar or Straw Substituting Chemical Fertilizer Increase the Risk of Phosphorus Loss in Subsurface Runoff in Sloping Farmland

The purple soil slope farmland is an important agricultural land in southwest China but is also one of the main sources of agricultural non-point source pollution in the Three Gorges Reservoir area. Taking reasonable measures to control the loss of soil nutrients is of great significance to the treatment of non-point source pollution in the region. Here, a three-year (2018-2020) field runoff experiment was conducted to monitor and evaluate the phosphorus (P) loss in sloping farmland via surface runoff (i.e., surface flow, 0-20 cm) and subsurface runoff (i.e., subsurface flow, 20-60 cm), with five treatments including no fertilization (CK), conventional fertilization (CF), optimal fertilization (OF), biochar combined with 85% of OF (BF), and straw combined with 85% of OF (SF). The results showed that fertilization application reduced the sediment yields and surface runoff flux but increased the subsurface runoff flux. The total loss flux of phosphate (PO3-4-P), total phosphorus (TP), and particulate phosphorus (PP) in surface flow were the highest in the BF treatment and the lowest in the SF treatment. All fertilization applications increased the P loss fluxes in subsurface flow relative to that in CK. The highest PO3-4-P and TP loss flux in subsurface flow was found in the BF (213.88 g·hm-2 and 694.54 g·hm-2, respectively) treatment, followed by that in the OF and SF treatments. Redundancy analysis (RDA) results showed that surface runoff flux and biochar application were the main factors contributing to increased P loss in surface flow, and subsurface runoff flux was the main factor contributing to increased P loss in subsurface flow. In summary, the SF treatment reduced the amount of sediment yield and surface runoff flux in sloping farmland of purple soil and was the most effective for controlling P loss, whereas the risk of subsurface runoff flux requires further attention.

Automatic mapping of gully from satellite images using asymmetric non-local LinkNet: A case study in Northeast China

Gully erosion can lead to the destruction of farmland and the reduction in crop yield. Gully mapping from remote sensing images is critical for quickly obtaining the distribution of gullies at regional scales and arranging corresponding prevention and control measures. The narrow and irregular shapes and similar colors to the surrounding farmland make mapping erosion gullies in sloping farmland from remote sensing images challenging. To implement gully erosion mapping, we developed a small training samples-oriented lightweight deep leaning model, called asymmetric non-local LinkNet (ASNL-LinkNet). The ASNL-LinkNet integrates global context information through an asymmetric non-local operation and conducts multilayer feature fusion to improve the robustness of the extracted features. Experiment results show that the proposed ASNL-LinkNet achieves the best performance when compared with other deep learning methods. The quantitative evaluation results in the three test areas show that the F1-score of erosion gully recognition varies from 0.62 to 0.72. This study provides theoretical reference and practical guidance for monitoring erosion gullies on slope farmland in the black soil region of Northeast China.

Characteristics of agricultural phosphorus migration in different soil layers on purple soil sloping cropland under natural rainfall conditions

Limited by the current monitoring and collection methods of subsurface flow data, the characteristics of phosphorus (P) migration loss in different soil layers on sloping cropland under natural rainfall conditions need to be clarified. In this study, a reliable U-trough collection method was used to explore P migration losses in different purple soil layers (L0: surface, L1: 0–20 cm, L2: 20–40 cm, and L3: 40–60 cm) for purple soil sloping cropland during a field monitoring campaign spanning two calendar years under natural rainfall conditions. The results suggested that the annual surface P loss load was 1.08 kg*ha−1*yr−1, where 92.1% was particulate P. The annual leaching loss load of total P from the L1 layer was 3.55 kg*ha−1*yr−1, where 74.2% and 10.5% were intercepted by the L2 and L3 layers, respectively, to increase the in situ soil P stocks. Only 15.3% of L1’s annually leached P, and only half the surface P loss load (L0), was lost to underground water. Heavy-rain events on the purple soils in the studied sloping cropland induced 43.9% of the annual surface P loss load. In contrast, 36.1%, 30.5%, and 30.3% of P’s eventual annual leached loss loads resulted from heavy, moderate, and torrential rain events, respectively. The maize season was the main period of surface and subsurface P migration loss. Due to the limitation of experimental conditions, the results of this experiment could not represent the soil phosphorus migration process in the natural purple slope farmland in nature, but it could partially represent the soil phosphorus migration in the newly cultivated purple sloping cropland in Chongqing.

Effects of rainfall pattern and soil surface roughness on surface–subsurface hydrological response and particle size distribution of red soil slope

Water erosion is strongly affected by rainfall pattern and soil surface roughness (SSR), the available information is inadequate to understand the influences of both on erosion processes and mechanisms. Four simulated rainfall patterns as constant (CR), increasing (IR), decreasing (DR), and rising-falling (RFR) with the same total rainfall amount (180 mm) and duration (180 min) were designed and applied to two soil surface conditions (smooth and rough) with the slope gradient of 15°. The response and generation of surface flow were positively correlated with the initial rainfall intensity of different rainfall patterns. The surface flow generation ranked as: DR > CR > RFR > IR, and the subsurface flow was the opposite. The CR pattern produced the lowest sediment yield, which was around 46.7% of the average soil loss for the varying-intensity rainfall patterns. SSR significantly promoted surface flow generation and sediment production under varying-intensity rainfall patterns, the surface flow coefficient and soil loss rate of the rough surface were 0.6%–13.1% and 3.20–11.27 g m−2 min−1 higher than that of the smooth surface. SSR inhibited the transport of sand particles and promoted the enrichment of clay particles. Under constant and variable rainfall patterns, the average content of clay particles of the rough surface was 2.8% and 0.9% more than that of the smooth surface, respectively. SSR could decrease fine particles and increase coarse particles in the eroded sediment, but only functioned under the rainfall patterns with lower initial rainfall intensity. Through comprehensively considering the effects of rainfall pattern and SSR, the stream power was the best hydraulic parameter for predicting the soil loss rate. The results are beneficial to the investigation of soil erosion in agricultural sloping farmland caused by natural rainfall events.

Transportation of fine particles controlled by particles flocculation is a key feature of soil erosion on gentle slope land

During water erosion, selective transport of eroded sediments reduces the fertility of surface soil and exacerbates the risk of waterbody pollution. At present, sloping farmland >10° (SFL10), which easily causes soil erosion, is the main research object. However, there has been relatively little focus on gentle slope lands (GSL). GSL refers to large fields with slope gradients of <6° divided by ditches, roads, and ridges, which can meet the requirements of mechanized production and intensive land management. In this study, to clarify the distribution and selectivity characteristics of the eroded sediment on GSL, natural rainfall experiments were conducted on GSL of 2° (S1), GSL of 5° (S2), and SFL of 12° (S3), where S3 was set as the control. Our results have demonstrated that although fine particles (<20 μm) were the main component of the eroded sediment on the GSL and SFL10, accounting for approximately 70–90%, there were differences in the enrichment ratio (ER) of fine particles. The ERs of <2 and 2–20 μm particles from S1 were significantly higher than those from S3 (P < 0.05). The <2 μm particles were predominantly transported as aggregates, and 2–20 μm particles were predominantly transported as single particles. Furthermore, the ERs of <2 and 2–20 μm particles from S2 were significantly lower than those from S1 owing to the influence of sediment particles undergoing flocculation. This demonstrates that selective transportation of fine particles controlled by particle flocculation is a key feature of soil erosion on GSL. When sediment is flocculated to a low degree, selective transportation of fine particles is more pronounced. Even on farmland with a slope of 2°, water erosion also results in the loss of many fine particles.

Effects of vegetation restoration on soil aggregates, organic carbon, and nitrogen in the Loess Plateau of China

Understanding the responses of soil aggregate stability and nutrient stoichiometry to vegetation restoration is essential for the ecosystem in the Loess Plateau, China. To explore the influence of vegetation restoration on soil aggregate stability and nutrient stoichiometry, we established a series of sample plots across five vegetation restoration types [sloping farmland (SFL), woodland (WL), grassland (GL), shrub land (SL), and terraced fields (TCE)], and measured the particle size distribution, stability, and organic carbon (OC) and total nitrogen (TN) content of soil aggregates. Vegetation restoration significantly affected particle size, stability, and OC and TN stocks of soil aggregates at depths of 0–40 cm. Compared with that in SFL, the quality fraction of macro-aggregates in WL, GL, SL, and TCE was 215.47%, 245.82%, 189.83%, and 95.06% greater, respectively, whereas the aggregate stability (indicated by the mean weight diameter) was 109.71%, 22.83%, 71.84%, and 77.67% greater, respectively. Vegetation restoration in WL, GL, and TCE significantly increased the OC content at 0–40 cm depth and the TN content at 0–60 cm depth. Aggregates > 0.25 mm dominated the particle size distribution in all vegetation restoration types, and had the highest OC and TN stocks; minor aggregates were the main source of OC and TN accumulation. A simulated rainfall experiment confirmed that an increase in soil aggregates (>0.25 mm) was associated with greater aggregate stability. Our findings suggested that soil aggregates > 0.25 mm are optimal for stabilizing soil aggregates, and increasing OC and TN stocks, in the Loess Plateau.

Roles of soil surface roughness in surface–subsurface flow regulation and sediment sorting

Tillage-induced soil surface roughness (SSR) and rainfall interactions determine the process of water erosion. In this study, long-duration rainfall simulations were conducted to investigate the effect of SSR on the processes of surface–subsurface flow generation and soil loss, flow hydrodynamics, sediment sorting and transport on the steep red soil sloping farmland, southern China. Rainfalls with intensities of 30, 60, and 90 mm h−1 with duration of 180 min were applied to two soil surfaces (smooth and rough) with the slope gradient of 15°. Lesser surface flow and more subsurface flow were generated on the rough surface, which also accelerated the initial flow response and erosion stage advancement. The reduction effect of SSR on the sediment yield was significant under light rain or in the sheet erosion stage, while was limited when the rainfall intensity became stronger or entering the rill erosion stage. Differences in the spatial variability of soil crusts and the spatial distribution of rill networks were the main agents. Stream power took roughness factor into consideration well, thus was identified as the best hydraulic parameter for the prediction of soil loss rate. The investigation of particle size distribution of the eroded sediment showed the contents of sand, silt and clay changed from 15.9%, 64.9%, and 19.2% (average value of the original soil) to 22.9%, 53.1%, and 24% for the smooth surface, and to 37.8%, 42.1%, and 20.2% for the rough surface (average value of the eroded sediment). The selective and degrading effects of SSR on sediment particles were represented well. The rough surface was more inclined to transport clay particles than the smooth surface in the former period of erosion. Sand particles instead become more enriched with the extension of rainfall time. The results are beneficial for controlling the water erosion on agricultural sloping farmland.

The patchiness of soil 13C versus the uniformity of 15N distribution with geomorphic position provides evidence of erosion and accelerated organic matter turnover

Farming on hillslopes often affects the accumulation and loss of soil organic matter (SOM) depending on slope position and cropping patterns. Most hillslope studies focus on soil movement to characterize SOM turnover under erosive conditions. In this study, we trace erosion and characterize agronomic practices erosive impacts on SOM translocation and transformation along geomorphic positions. To achieve this, we assessed the horizontal distribution (upper 15 cm) and vertical distribution (to 100 cm profiles) of soil δ15N and δ13C isotope abundance individually. We mapped the spatial distribution of δ13C, δ15N, and SOM turnover indices as a novel approach to tracing erosion and degradation of SOM in the field. Except for tillage (conventional vs. reduced tillage), other individual agricultural practices (residue removal with no cover crop vs. retaining residuals, cover cropping, and fertilizer 0, 40, and 80 kg ha-1 nitrogen) caused no significant shifts in δ15N and δ13C values in topsoil (0–15 cm). Among the evaluated factors, topography and depth predicted soil δ15N and δ13C profiles. Trends in δ13C vs. δ15N showed a wider range of δ13C values in topsoil of upslope plots under reduced tillage, while in the depositional location, conventional tillage had the same effect. This suggests erosion under reduced tillage occurred. Erosion and accelerated decomposition gradually slowed δ13C enrichment with soil depth. Digital soil mapping approach depicted low continuity of δ13C vs. high continuity of δ15N with geomorphic position We attributed the intermediate δ13C values, and steeper slope of δ13C against logarithm of soil organic carbon (SOC) across the slope to erosion and high SOM turnover, particularly of recently added plant inputs. Current results support the prediction of intensive vs. conservation practices’ effects on upslope soil stability and the fate of SOM in both topsoil and at depth of sloping farmlands.

Laboratory-Scaled Investigation into Combined Impacts of Temporal Rainfall Patterns and Intensive Tillage on Soil and Water Loss

Many studies have focused on the impacts of rainfall duration and intensity, while overlooking the role of rainfall patterns on intensive tillage erosion in hilly agricultural landscapes. The objective of this study was to determine the combined effects of rainfall patterns and tillage erosion on surface runoff and soil loss on sloping farmland in the purple soil area of China. Five simulated rainfall patterns (constant, rising, falling, rising–falling, and falling–rising) with the same total precipitation were designed, and the intensive tillage treatment (IT) and no-tillage treatment (NT) were subjected to simulated rainfall using rectangular steel tanks (2 m × 5 m) with a slope of 15°. To analyse the differences in the hydrological characteristics induced by tillage erosion, we calculated the flow velocity (V), Reynolds number (Re), Froude number (Fr), and Darcy–Weisbach resistance coefficient (f). The results indicate that significant differences in surface runoff and sediment yield were found among different rainfall patterns and rainfall stages (p &lt; 0.05). The falling pattern and falling–rising pattern had a shorter time gap between the rainfall initiation and runoff occurrence as well as a larger sediment yield than those of the other rainfall patterns. The value of f varied from 0.30 to 9.05 for the IT and 0.48 to 11.57 for the NT and exhibited an approximately inverse trend to V and Fr over the course of the rainfall events. Compared with the NT, the mean sediment yield rates from the IT increased the dynamic range of 8.34–16.21% among the different rainfall patterns. The net contributions of the IT ranged from 2.77% to 46.39% in terms of surface runoff and 10.14–78.95% in terms of sediment yield on sloping farmland. The surface runoff and sediment yield were positively correlated with rainfall intensity, V, and Fr, but negatively correlated with f irrespective of tillage operation (p &lt; 0.05). The results showed that the tillage erosion effects on soil and water loss were closely related to rainfall patterns in hilly agricultural landscapes. Our study not only sheds light on the mechanism of tillage erosion and rainfall erosion but also provides useful insights for developing tillage water erosion prediction models to evaluate soil and water loss on cultivated hillslopes.

Predicting soil erosion and deposition on sloping farmland with different shapes in northeast China by using 137Cs

Slope shape has an important influence on soil erosion. However, the distribution of erosion and deposition on sloping farmland with different shapes is still unclear. This severely restricts the soil loss evaluation and protection of Mollisol resources in northeast China, where sloping farmland (<10°) accounts for 60 % of the cultivated land. In this study, the 137Cs technique combined with wavelet analysis theory was employed to study the spatial distribution characteristics of erosion–deposition rates along three slopes with straight, convex, and concave shapes in northeast China. The results indicated that the average erosion rates of the three slopes were in the following order: convex > straight > concave. The soil erosion and deposition rates fluctuated along the slope length. The primary fluctuation periods in the straight slope, convex slope and concave slope were 45.1 m, 55.0 m, and 40.4 m, respectively. Three relationships of coupled effects of slope gradient and slope length on straight, convex and concave slope were established and verified. It can be concluded that the relationship between the soil erosion rate and slope length was not simple monotonous but showed a certain periodic fluctuation, which was related to the change in transport capacity of runoff on the slope. The change in the erosion–deposition rate with slope length in a straight slope shape can be described by the cosine function. The cumulative soil erosion–deposition rates along the slope had very significant binary power function relationships with both slope length and gradient on convex and concave slopes. The coupled effects of slope gradient and length on soil erosion–deposition for different slope shapes should be fully considered for soil erosion prediction. This study could provide theoretical support for improving erosion prediction models and a scientific basis for the rational arrangement of soil and water conservation measures on slopes at appropriate locations.

Laws Governing Nitrogen Loss and Its Numerical Simulation in the Sloping Farmland of the Miyun Reservoir.

Surface flow (SF) and subsurface flow (SSF) are important hydrological processes occurring on slopes, and are driven by two main factors: rainfall intensity and slope gradient. To explore nitrogen (N) migration and loss from sloping farmland in the Miyun Reservoir, the characteristics of total nitrogen (TN) migration and loss via SF and SSF under different rainfall intensities (30, 40, 50, 60, 70, and 80 mm/h) and slope gradients (5°, 10°, and 15°) were studied using indoor stimulated rainfall tests and mathematical models. Nitrogen loss via SF and SSF was found to increase exponentially and linearly with time, respectively, with SSF showing 14-78 times higher loss than SF. Under different rainfall intensities, SSF generally had larger TN loss loading than SF, thereby indicating that SSF was the main route for TN loss. However, the TN loss loading proportion via SF increasing from 14.03% to 35.82% with increasing rainfall intensity is noteworthy. Furthermore, compared with the measurement data, the precision evaluation index Nash-Suttcliffe efficient (NSE) and the determination coefficient (R2) of the effective mixing depth model in the numerical simulation of TN loss through SF in the sloping farmland in the Miyun Reservoir were 0.74 and 0.831, respectively, whereas those of the convection-dispersion equation for SSF were 0.81 and 0.811, respectively, thus indicating good simulation results. Therefore, this paper provides a reference for studying the mechanism of N migration and loss in sloping farmland in the Miyun Reservoir.