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Mesoplastic (MaP) and macroplastic (MeP) coming from plastic mulching tend to cause negative effects on biota in ecosystems. However, it is still not clear how field management influences the distribution of MeP/MaP in soils. In this study, MeP/MaP was investigated in 0–20 and 20–30 cm soil layers of three vegetable fields (3.4–6.5 ha) after 13 years plastic-mulching in Mollisols of Northeast China under different management methods (MM) of fertilization and tillage frequency. The tillage frequency was MM2 > MM1 > MM3, while the fertilization was MM1 > MM2 > MM3. The results showed that polyethylene (PE), polypropylene (PP), polystyrene, polyvinyl chloride, polyethylene terephthalate (PET), polyamide, melamine-formaldehyde resin and polyether urethane were found in soil, and PE (>83.76%, from plastic mulching) was the predominant type of MeP/MaP. MeP abundance was significantly (p < 0.05) higher in MM1 and MM2 than that in MM3 in the 0–20 cm soil layer. MM1 and MM2 had the highest abundance of MeP/MaP of size <4 cm2 and 4–16 cm2, while MM3 had the highest abundance at the size >16 cm2. The broken index of MeP/MaP was significantly (p < 0.05) lower in MM2 compared with MM1 and MM3 in the 20–30 cm soil layer. Both tillage frequency and fertilization accelerate the breaking of plastics, especially since the influence was stronger from fertilization. Compared with original plastics, the PE, PP and PET's carbonyl index was significantly (p < 0.05) higher in the three MMs. Generally, fertilization and frequent tillage can reduce the physical effects of large-sized plastic debris on crop growth and increases the negative effects of small-sized plastic and new pollutants formed on biota in the agroecosystems. MeP/MaP recycling should be strengthened, and the irrigation and rotation of farmland should be carried out when the wind speed is weak to avoid plastic invasion. [Display omitted] • Plastics of PE (>83%), PP, PS, PVC, PET, PA, MF and PEUR were found in farmland. • Fertilization and tillage increased the abundance of mesoplastics. • Fertilization can reduce the physical effect of large-sized plastics on crop growth. • CI of plastic positively correlated with tillage frequency and fertilization dose. • Oxidation of plastics by fertilization was greater than the tillage. [ABSTRACT FROM AUTHOR]

Natural vegetation restoration (NVR) highly relates to the development of gully erosion, and is mainly determined by both the soil properties and species competition in the gullies. However, it is still not clear what are the key factors influencing on the vegetation restoration in the gullies with the poor soil properties (e.g. low soil organic matter and nutrients) under the special hydrological process (e.g. high runoff intensity and long flow duration). In this study, soil total organic carbon (SOC), total nitrogen (TN), available nitrogen (AN), ammonium nitrogen (NH 4 +-N), nitrate nitrogen (NO 3 −-N), total phosphorus (TP), available phosphorus (AP), pH, soil moisture (SM) were investigated, and both regression and structural equation model analysis were used for detecting how soil properties and species competition influence the herbaceous plants restoration in the poor quality of Mollisols in gullies of Northeast China. The results show that, (1) influence of NH 4 +-N, AN, TN, pH on biomass was stronger in 0–10 cm than that in 10–20 cm soil depth, opposite was stronger in 10–20 cm than that in 0–10 cm soil depth for NO 3 −-N, SOC and SM (P < 0.05). (2) NH 4 +-N, NO 3 −-N, AN, TN, SOC, pH, C:N were all negative, while SM was positive to plant biodiversity in soil layers (P < 0.05). (3) SOM mainly mediates the TN and NH 4 +-N and then directly or indirectly influences on biodiversity and biomass, and P changed the species richness when AP >20 mg kg−1 in 10–20 cm soil depth. (4) Vegetation restoration was mainly determined by the dynamics of Elymus dahuricus Turcz. firstly, and then by Leymus chinensis (Trin.) Tzvel. at the early of vegetation restoration. Generally, the heterogeneity of SOC and SM in soil layers and AP in deep soil layer was the key factors determining NVR in the gullies of Mollisols watershed. At the end of paper, the NVR process in Moillosols in gullies was classified as four stages, and each stage was depicted in detail. [Display omitted] • Influence of N, SOC and SM on plant biomass differed from plant biodiversity. • SOM mediates the N form and content and then influences on biomass and biodiversity. • SOC and SM in 0–20 cm soil layers mainly determine natural vegetation restoration. • P changed the species richness when AP >20 mg kg−1 in 10–20 cm soil depth. • Increasing Poaceae could be optimal method to accelerate early vegetation restoration. [ABSTRACT FROM AUTHOR]

Agricultural films composed of low-density polyethylene (LDPE) have been widely used in farmland, and LDPE microplastics (LDPE-MPs) produced from LDPE degradation can pollute soils and can exert negative effects on biota. Both nitrogen (N) and phosphorus (P) can alter the activity of soil microorganisms and may alter the LDPE-MP degradation process in soils. In this study, LDPE-MP surface morphology, particle size, abundance and mass in a mollisol were evaluated after the application of a gradient of N and P fertilizer in a laboratory incubation experiment. The results showed the following: (1) LDPE-MP particles became fragmented into smaller debris with a coarse surface after 40 days of incubation, and the effect was more obvious with increased P or N application; (2) high N and P fertilization significantly reduced the abundance of LDPE-MP particles >100 μm by 38.5–50.0% and increased the abundance of LDPE-MP particles <20 μm by 43.2–59.5% after 40 days of incubation; (3) high N and P fertilization significantly increased the mass of LDPE-MP particles <75 μm by 25.5–60.1% and decreased the mass of LDPE-MP particles >150 μm by 32.4–37.5%; (4) the mass of LDPE-MPs decreased with increasing incubation time after N and P fertilization, which could be simulated by exponential models (p < 0.05), LDPE degradation was rapid in the first 20 days after N or P fertilization, and both N and P caused a "priming effect" of LDPE degradation; and (5) N and P fertilization increased both the biodiversity and abundance of several predominant genera of soil microorganisms that degrade LDPE. Therefore, N and P fertilization can accelerate LDPE-MP degradation, and the relatively large amounts of fine debris from degraded LDPE-MPs can be problematic for the environment and soil biota. LDPE-MP pollution should be strictly controlled in mollisols, and the degradation mechanisms of LDPE-MPs warrant further study. Unlabelled Image • N and P fertilization changed the mass fraction of LDPE-MP particles size in soils. • N and P fertilization changed the abundance fraction of LDPE-MP particles size. • LDPE-MP decreased with incubation days can be simulated by exponential models. • LDPE degradation was rapid in the first 20 days after N or P fertilization. • N and P application could cause a "priming effect" on LDPE degradation. [ABSTRACT FROM AUTHOR]

• Polyethylene (PE) of light density microplastic (LDMP) was found in farmland. • LDMPs positively correlated to MAP at large scale, while not obvious at small scale. • Low BD tends to increase LDMPs loss by interflow. • LDMPs were mainly moved by surface soil-water loss (96%). Plastic pollution, especially microplastic (MP), which is small in size (<5 mm) is one of the main environmental problems in global ecosystems and can cause harm to organisms. Low-density plastic has been widely used in farmlands, but the factors that influence Low-density microplastic (LDMP) distribution are still not clear. In this study, both field investigations at small and large scales and laboratory simulations, and both geostatistics and classical statistics were used to examine LDMP distributions and the main driving factors in farmland soils. The results showed the following. (1) Only polyethylene (PE) of LDMP was found in farmland. (2) The means of LDMP weight content (LDMP-W), LDMP abundance (LDMP-AB) and LDMP area content (LDMP-A) were 0.27 mg kg−1, 107 N kg−1 and 12.6 mm2 kg−1 in mollisol farmlands, respectively. (3) LDMPs were positively correlated with macroplastics (MAP) at the large scale, while any correlations were not obvious at small scales. (4) LDMPs were not only transported by surface soil–water loss (>96%) but were also transported by infiltration through soil pores (<4%). (5). LDMP loss increased with soil bulk density (BD) increasing, and low BD tends to increase LDMP loss by interflow. (6) LDMP distribution was not only influenced by water movement but also maybe influenced by microorganisms and crops. For LDMP pollution control, the focus on both surface soil–water loss and the infiltration processes is necessary, and a combination of the functions of microorganisms and crops probably accelerate LDMP decomposition in soils. [ABSTRACT FROM AUTHOR]

Gully erosion has been widely studied during the rainy season due to soil loss that seriously reduces arable area and decreases soil quality. However, very few publications have focused on gully slope erosion (GSE) during freeze thaw cycle (FTC). In this study, GSE on both active and stable gullies in Mollisol fields was investigated by 3D-photogrammetry. Soil bulk density (BD), soil moisture (SM), soil temperature (ST), daily maximum difference in soil temperature (MDT), saturated water (SW), field capacity (FC), soil organic carbon (SOC), soil total nitrogen (TN), water-stable soil aggregate (WA), vegetation cover rate (VC), root dry weight (RW), root length (RL), slope length (SL) and slope steepness (SS) were compared before- and after FTCs. The main results are as follows: (1) combined with both front and profile views, 3D photogrammetry can be used to monitor GSE; (2) GSE mainly occurred at the early stage of FTCs (approximately 80%) and was mainly determined by snowmelt of both the gully slope and farmland and was driven by the solar radiation in activity gully; (3) the high ST in surface soil layers (0–5 cm) of active gullies accelerated the GSE; (4) GSE on the active gully slope was 7.3–9.8 times greater than that on the stable gully slopes; (5) the plough pan as the important layer can effectively reduce GSE at upper slope positions in an active gully; (6) low values of VC, BD, SOC, RW, RL and macro-WA and high values of SL, SW and MDT in the middle of the gully slope typically accelerate the GSE; (7) the index SS*SL/VC can be used to predict GSE on Mollisol gully slopes. Generally, GSE was greatest after FTCs compare to the soil loss tolerance in the Mollisol region, especially in the middle slope position of the active gully, and should urgently be controlled. Unlabelled Image • 3D photogrammetry method can be used to monitor gully slope erosion (GSE) during FTCs. • GSE was mainly determined by snowmelt and occurred at early FTCs. • Soil properties were easily changed to accelerate GSE on slope with high temperature. • GSE mainly occurred at the middle slope and influenced by plough pan in active gully. • Parameter of SS*SL/VC can be used to predict soil loss on Mollisol gully slopes. [ABSTRACT FROM AUTHOR]

Freeze-thaw cycles (FTCs) change the soil physicochemical properties and biogeochemical cycles and possibly also change the spatial heterogeneity of soil total nitrogen (TN) in the watershed. In this study, 912 soil samples were collected at 0–5 cm, 5–10 cm and 10–20 cm soil depths in the autumn and the spring of next year after FTCs of 2016–2017 and 2017–2018 in a Mollisol watershed (1.86 km2) of northeast China. The field investigations combined with classical statistics and geographically weighted regression kriging (GWRK) were used to explore the spatiotemporal distribution of TN before and after FTCs. Terrain information (e.g., slope aspect) and land management (e.g., tillage method) was main covariates were used for GWRK. The results showed the following. (1) TN decreased by 3.7–5.7% after FTCs at 0–20 cm soil depths at the watershed scale, decreasing more than 60% of the total watershed area. (2) The spatial pattern of TN did not change in the field with slope aspects and tillage methods after FTCs, but it changed with slope steepness and land uses. (3) TN was mainly influenced by snowmelt erosion during FTCs. TN increased in parts of the top slope, at land use intersection, in gully banks and at the watershed outlet. (4) Simulation accuracy of GWRK was higher than ordinary kriging (OK) for predicted TN at 0–20 cm soil depths before and after FTCs. (5) Spatial distribution of soil TN after FTCs can be predicted (R2 = 0.521, p < 0.0001) and validated (R2 = 0.494, p < 0.0001) using the data before FTCs based on GWRK. Generally, to reduce N loss and increase farmland fertility after FTCs, conservational techniques, e.g., tillage and straw amendment, could be used, especially in the middle slope positions. Moreover, fertilization should be appropriately reduced in parts of the watershed after FTCs, especially on the top slope, land use intersection and watershed outlet. Unlabelled Image • Mean TN decreased 3.7–5.7% at watershed scale, and over 60% of area decreased after FTCs. • Snowmelt erosion was the key factor influencing on TN change during the FTCs. • GWRK has a higher accuracy than OK to estimate TN before and after FTCs. • Soil TN after FTCs can be coarsely predicted using the data before FTCs. • Fertilization on top slope, intersection of land use, watershed outlet in spring needs control. [ABSTRACT FROM AUTHOR]

• GWRK was employed to reveal the spatial patterns of TP at the watershed scale. • The spatial autocorrelation of TP decreased by 5.9% after FTCs. • TP decreased in 85% of the watershed area after FTCs. • The mean value of TP decreased by 9.5% in the watershed after FTCs. • An equation was developed and used to roughly predict TP after FTC (R2 = 0.72). Freeze-thaw cycles (FTCs) change soil physiochemical properties and biogeochemical processes and inevitably influence the spatial distribution of soil phosphorus (P). In this study, a field investigation was conducted on the Mollisol soil of the Guangrong watershed from 2016 to 2018 to clarify the effect of FTCs on the spatial distribution of total phosphorus (TP) at soil depths of 0–5, 5–10 and 10–20 cm. A laboratory incubation experiment was conducted to reveal the effect of FTCs on TP in soil profiles (0–30 cm) in Mollisols. The results showed that (1) the spatial autocorrelation (nugget to sill ratio) of TP decreased by 5.92% after the FTCs while the spatial variance (coefficient of variation) increased by 17.19%. The TP in 85% of the watershed area decreased after the FTCs, and the mean content of TP decreased by 9.53%. These changes were mainly influenced by land use types, topographical factors, soil properties and human activities. (2) TP increased in the intersection between farmland and forestland (0.01 g kg−1) after the FTCs, while TP decreased both in the areas near the hydrological channel (0.06 g kg−1) and at the outlet of the watershed (0.13 g kg−1). Compared with down-slope tillage, maize planting, south-facing slopes and low vegetation coverage areas, the cross-slope tillage, soybean planting, north-facing slopes and high vegetation coverage areas reduced TP losses by 56.1%, 19.5%, 115.8% and 141.9%, respectively, in the 0–20 cm soil layer. (3) The effects of FTCs on TP in soil profile were mainly influenced by the soil moisture content, FTC frequency and soil bulk density in the laboratory incubation experiment. TP variability showed a V-shaped trend as the number of FTCs increased, and decreased as the initial moisture content increased at 1.1 g cm−3 of soil bulk density. (4) An equation based on the TP and mean value of normalized difference snow index, normalized difference vegetation index, ferrous minerals index and normalized difference soil moisture index from the freezing period to the thawing period was built to roughly predict the TP after FTCs (R2 = 0.72). Generally, the TP tended to decrease during both the freezing stage and the thawing stage in the field. Areas with down-slope tillage, existing maize fields, south-facing positions, low vegetation coverage and high snow coverage should be focused on to reduce P losses during FTCs. [ABSTRACT FROM AUTHOR]