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This article introduces a simple and cost-saving method developed to extract, distinguish and quantify light density microplastics of polyethylene (PE) and polypropylene (PP) in soil. A floatation method using distilled water was used to extract the light density microplastics from soil samples. Microplastics and impurities were identified using a heating method (3–5 s at 130 °C). The number and size of particles were determined using a camera (Leica DFC 425) connected to a microscope (Leica wild M3C, Type S, simple light, 6.4 ×). Quantification of the microplastics was conducted using a developed model. Results showed that the floatation method was effective in extracting microplastics from soils, with recovery rates of approximately 90%. After being exposed to heat, the microplastics in the soil samples melted and were transformed into circular transparent particles while other impurities, such as organic matter and silicates were not changed by the heat. Regression analysis of microplastics weight and particle volume (a calculation based on image J software analysis) after heating showed the best fit (y = 1.14x + 0.46, R 2 = 99%, p < 0.001). Recovery rates based on the empirical model method were > 80%. Results from field samples collected from North-western China prove that our method of repetitive floatation and heating can be used to extract, distinguish and quantify light density polyethylene microplastics in soils. Microplastics mass can be evaluated using the empirical model. [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]

Soil pollution severely threatens agro-ecosystem stability. It is important to accurately understand the status of farmland pollution in order to protect national food safety and human health. However, information of the combined pollution level of Chinese farmland soil and associated human health risk at the national scale is relatively lacking. In this study, 5597 samples from 1781 farmland soil sites were obtained from 553 reports and combined into pollution databases of heavy metals, organochlorines, and polycyclic aromatic hydrocarbons. Based on the data obtained, this paper demonstrated the current pollution status of farmland soil, and assessed the subsequent human health risk. Results showed that the combined pollution ratio of Chinese farmland soil was 22.10%, with 1.23% of severe pollution level. Moreover, the total non-carcinogenic hazard quotients of farmland soil pollution were within the safety threshold for adults, but there was a slight non-carcinogenic risk for children. For adults, the ratio of total farmland area to total carcinogenic risk quotients above the safety threshold of 1 × 10−5 was only 1.02%, but for children, the ratio was as high as 20.75%. On the other side, food crop and vegetable plantations were the priority control farmland soil compared to other types. Meanwhile, Yunnan, Hunan, Anhui, Henan, and Liaoning were selected as the priority control provinces due to their severe pollutions and high human health risks. This study has provided a comprehensive pollution and health risk assessment. Furthermore, the spatial distribution might provide as the scientific support for accelerating the mapping of soil pollution in China, as well as developing the policy for the contaminated farmland soil management. Unlabelled Image • 5597 samples from 1781 farmland soil sites are reviewed. • 22.1% of China farmland soils are polluted at varying degrees. • 20.8% of soil poses carcinogenic risk in children, much higher than in adults. • The potential carcinogenic risk was homologous to farmland soil pollution in China. [ABSTRACT FROM AUTHOR]

Abstract Agricultural multifunctionality is increasing interest and importance under the environmental change, which influences the sustainability of agricultural systems. However, research on how the agricultural multifunctionality is being temporally adjusted under the process of rapid urbanization remains limited. Here, we use the Yangtze River Delta, one of the newest metropolitan agglomerations globally, as study area to investigate the threats of modern urbanization to traditional agriculture. This study assessed changes to farmland area and the agricultural multifunctionality of 16 cities in the delta during 1995–2015. The results show that: (1) 87.1% (690, 200 hm2) of farmland area was lost because of urban sprawl over the last 20 years; (2) the total value of agricultural multifunctionality in the delta had increased by 23.2%, which was mainly attributed to a significant increase in food provision and cultural leisure values; (3) the key factor affecting the spatial differentiation of agricultural multifunctionality changed from agricultural labour in 1995 to gross domestic product in 2005 and 2015; and (4) Socio-economic conditions and natural resources determined the adaptive change model of agricultural multifunctionality in different groups of cities. These results illustrate that agricultural multifunctionality is being adjusted to rapid urbanization through the intensification and trade-off of the multiple functions in agricultural system. Therefore, to foster the sustainable development of agriculture in metropolitan agglomerations, future land use policy should focus on both urban control and promoting agricultural multifunctionality. Ongoing transformation practices, such as land consolidation, should aim to improve the bio-physical and socio-economic functions of farmland in the delta. Future research should focus on developing locally suitable strategies based on the adaptive mechanisms of agricultural multifunctionality under changing environments in different cities. Graphical abstract Unlabelled Image Highlights • Changes to farmland and multifunctionality were assessed in the Yangtze River Delta. • Farmland loss did not cause food provision to decline from 1995 to 2015. • Key factors affecting multifunctionality changed from agricultural labour to GDP • Intensification and trade-offs offset the impact on agricultural multifunctionality. [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]

In the ecological restoration of mine dumps, soil carbon stock (SCS) improvement is an important issue. The type of land use and management approach taken can have a great influence on this issue. On the Loess Plateau, different crops have been cultivated on reclaimed land; however, the effect of long-term crop cultivation on SCS is poorly understood. To address this issue, a field investigation of mine dumps was performed at the Kee Open Pit Mine in Shanxi Province, China. Four sites utilizing different land management methods were analyzed: no reclamation (NR), reclamation with no crop cultivation (NC), and reclamation followed by 11 or 27 years crop cultivation (RC-11 and RC-27, respectively). SCS, associated soil properties (total nitrogen (TN), total phosphorus (TP), total potassium (TK), moisture content (MoiC), and pH), plant community (species composition, plant diversity, and traits), and microbial community operational taxonomic units (OTUs) of fungi and bacteria were determined by field investigation and laboratory analysis. Redundancy analysis was used to show the relationship between SCS and other environmental variables. Results varied by soil depth. At the depth range of 0–20 cm, the SCS of RC-11 was significantly greater compared to that in NR and NC, by 14.64- and 2.25-fold, respectively; whereas compared to RC-27, it was higher by 52.78%. At the depth of 20–40 cm, NC has the largest SCS; the SCS of RC-27 was the lowest, which was less compared to that in NC by 43.64%. Redundancy analysis showed a positive relationship between the SCS and TN, TP, MoiC, as well as average plant coverage, while the bacterial OTUs were negatively related with the SCS. This research suggests the potential of mine dumps for crop cultivation, which could improve the SCS of the mining area on the Loess Plateau. Unlabelled Image • Soil carbon stock of mine dumps under different management was investigated. • The soil carbon stock of the dump after 11 years of cultivation was the highest. • Relationships between soil, plant and microbial community were analyzed. • Surface soil was more susceptible than deep soil to the effect of crop cultivation. [ABSTRACT FROM AUTHOR]