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• TN, pH and sand content were the key indicators for the minimum dataset of soil quality. • Soil quality decreases with cultivated ages while increasing from the upper to the lower slope. • SQI was primarily affected by the cultivation ages when not considering the lower slope. • For diverse slope positions, variations in key soil quality indicators need to be re-considered. Arable land use change and ages from natural forests alter soil quality, i.e., organic carbon and nutrient losses. Landscape fosters a more complicated spatial distribution of soil quality indicators by soil erosion, resulting in deposition at the lower slope. Although the soil quality index (SQI) has been widely used to assess soil quality, studies comparing the effects of cultivation ages and slope positions on soil quality evolution are rare. Here we report variations in soil quality and corresponding indicators under different cultivation ages (15-yr, 20-yr, and 30-yr) and sloping positions (upper-, middle-, and lower-slope) in the Mollisol region of China. We found a decreasing trend occurred for the soil organic carbon (SOC) and total nitrogen (TN) with cultivation ages. Simultaneously, from upper slope to lower slope position, an increasing trend occurred for the soil fertility properties (i.e., SOC, TN, available potassium-AK, total phosphorus-TP, and available phosphorus-AP), and a decreasing trend occurred for total potassium (TK) and pH. We found that TN, pH and sand content were the most representative indicators for the minimum data set, which represents soil quality under diverse cultivation ages. Moreover, the SQI decreased with increasing cultivation ages while increasing from the upper- to the lower slope. Notably, SQI was primarily affected by the cultivation ages (14.6%) with no considering lower slope positions. While the slope position was the main contribution to SQI (21.6%) with considering lower slope position. We highlight that although the minimum data set was the most feasible approach for assessing soil quality under different ages of cultivation in the Mollisol region. For diverse slope positions and elevations, variations in key soil quality indicators and their interactions are necessary to be re-considered and assessed due to the soil erosion and deposition processes. [ABSTRACT FROM AUTHOR]

[Display omitted] • Soil silt/clay and nutrients increased with increasing distance from the shelterbelt. • Downslope deposition lead to an increase in plow pan thickness and a decrease in bulk density. • Erosion rate was primarily affected by shelterbelt distance, followed by elevation. • Sites closer to shelterbelt warrant particular attention due to coarse-texture materials. Soil erosion is the most severe form of land degradation globally. Farmland shelterbelts are important for reducing erosion, especially erosion caused by the co-occurrence of water and wind. However, few studies have focused on how the distance from the shelterbelt associated with farmland topography affects the redistribution of soil quality indicators. The aims of this study is to reveal the relative importance of these two factors to soil quality under typical wind and water erosion conditions concurrent with the Songnen Plain, China. Topsoils (0–10 cm) were sampled at seven distances from the shelterbelt with three replicates, where topography heterogeneity was also considered. We found that the silt/clay content and soil nutrients at sites farther from the shelterbelt were significantly greater than those at sites closer to the shelterbelt (P < 0.05). Similarly, deposition was dominant at sites farther from the shelterbelt and downslope positions, while erosion was dominant at sites closer to the shelterbelt and upslope positions. Moreover, we discovered that the relative influence of distance from the shelterbelt and farmland elevation varied with individual soil quality indicators. Soil nutrients increased through the deposition of more fine-textured soil (silt/clay) positions farther from the shelterbelt. The downslope region responds to soil deposition by enhancing the plough pan thickness and lowering the bulk density and pH. Overall, distance from the shelterbelt and farmland elevation had interactive effects on soil quality, and erosion was primarily affected by distance from the shelterbelt (63.4 %), followed by elevation (22.7 %). Furthermore, the sites closer to the shelterbelt (i.e., 20 to 420 m) warrant particular attention due to the deposition of coarse-texture materials here. This work is crucial for an improved understanding of the synergistic effects of long-term water and wind co-occurrence on soil quality evolution. [ABSTRACT FROM AUTHOR]

Mollisols are of major importance for food security worldwide but are increasingly degraded by soil erosion. Mollisols in Northeast China have been converted into agricultural use only since the 19th century, but gullies are widely distributed. Gully erosion history, rates, and causes in this region remained unclear. We chose a study area with landforms and land‐use history typical for the central Mollisol region of Northeast China to estimate the initiation years and rates of gully erosion from 1968 to 2018 using aerial and satellite imageries. The outlet fan deposits of a large gully system were dated by Cesium‐137 (137Cs) and artifacts. Local farmers were interviewed to verify the results. Gully volumes were measured by a structure‐from‐motion technique using photos taken from an unmanned aerial vehicle. Our results showed that gully systems had already appeared on the steep slopes and along unpaved roads in 1968. They had become larger and more complex in 2018 by the upslope retreat of the main gullies and side gully formation. Gully incision started in the 1950s and 1960s when the original grassland and forest were completely converted into arable land. From 1968 to 2018, the gully density increased from 1.2 to 2.3 km km−2 and the gully heads retreated at speeds from 1.5 to 2.5 m yr−1. The soil loss from gully erosion ranged from 25.7 to 44.7 Mg yr−1 ha−1. These data demonstrate the severity of gully erosion in the Mollisol region of Northeast China and underline the importance of appropriate countermeasures. [ABSTRACT FROM AUTHOR]

Terracing of hillslopes is usually regarded as an effective measure to control soil erosion. Although it is often stressed that proper terrace construction and regular terrace maintenance are of great significance to prevent erosion on terraced hillslopes, examples of terrace-induced gully erosion are scarce. Field observations on terraced and partly abandoned hillslopes in the Black Soil Region of Northeast China, a region heavily affected by gully erosion since the middle of the 20th century, indicated that gully formation might be caused by terraces. In order to understand the impact of terracing on gully erosion, we selected several gullies to investigate the cause and timing of their triggering. We used a combination of field mapping, high-resolution digital terrain models, multi-temporal aerial photograph interpretation and interviews with local farmers. Our results showed that several gullies developed after terracing. Improper terrace design caused runoff concentration along terraces and ridges with mean inclination of 3.8%, which resulted in gully incision due to overtopping of terraces at low spots or due to the uncontrolled release of concentrated flow to adjoining unterraced hillslopes. The same processes are responsible for the persistent gully activity after abandonment and vegetation recovery. Furthermore, we showed how terraces affected gully morphology. Finally, we suggested appropriate countermeasures to stop further soil loss and land degradation on abandoned terraced hillslopes in NE China. Our findings are important as they demonstrate how poorly designed terraces may not only be ineffective but may even aggravate gully erosion. Unlabelled Image • Terracing modifies the drainage network and influences the location of gully erosion. • Erosional gaps in contour ridges release concentrated runoff. • Overland flow along graded terraces and contour ridges may induce gully erosion. [ABSTRACT FROM AUTHOR]