Abandoned farmlands are increasing due to socio-economic changes and land marginalization, and they require sustainable land management practices. Biocrusts are a common cover on the topsoil of abandoned farmlands and play an important role in improving soil stability and erosion resistance. The critical functions of biocrusts are known to mostly rely on their biofilaments and extracellular polymeric substances (EPS), but how these components act at microscopic scale is still unknown, while rheological methods are able to provide new insights into biocrust microstructural stability at particle scale. Here, bare soil and two representative types of biocrusts (cyanobacterial and moss crusts) developed on sandy (Ustipsamments) and sandy loam (Haplustepts) soils in abandoned farmlands in the northern Chinese Loess Plateau were collected at a sampling depth of 2 cm. Changes in the rheological properties of the biocrusts were analyzed with respect to their biofilament network and EPS contents to provide possible explanations. The rheological results showed that compared with bare soil, storage and loss moduli were decreased by the biocrusts on sandy soil, but they were increased by the biocrusts on sandy loam soil. Other rheological parameters tau max, gamma L, gamma YP, and Iz of biocrusts on both soils were significantly higher than those of bare soil, showing higher viscoelasticity. And the moss crusts had about 10 times higher rheological property values than the cyanobacterial crusts. Analysis from SEM images showed that the moss crusts had higher biofilament network parameters than the cyanobacterial crusts, including nodes, crosslink density, branches, branching ratio and mesh index, and biofilament density, indicating that the biofilament network structure in the moss crusts was more compact and complex in contrast to the cyanobacterial crusts. Additionally, EPS content of the moss crusts was higher than that of the cyanobacterial crusts on both soils. Overall, the crosslink density, biofilament density, and EPS content of the biocrusts were significantly and positively correlated with their gamma YP and Iz. The interaction between crosslink density and biofilament density contributed 73.2 % of gamma YP, and that between crosslink density and EPS content contributed 84.0 % of Iz. Our findings highlight the biocrusts-induced changes of abandoned farmland soil rheological properties in drylands, and the importance of biocrust biofilament network and EPS in maintaining abandoned farmland soil microstructural stability to resist soil water/wind erosion and degradation, providing a new perspective for sustainable management of abandoned farmlands.

Agricultural land has long been regarded as a resource for food production, but over time, the effects of climate change have reduced the ability of soil to produce food efficiently. Nowadays, farmers have moved from traditional to modern techniques of farming. Across the globe, plastic mulching has become widely used on farmlands. According to a few studies, the breakdown of plastic mulches releases microplastics (MPs) into the soil. Despite studies reporting the presence of MPs in soils, there are limited studies on the sources and impacts on soil organisms, plant growth, fruits, and human health. This study evaluated research articles collected from the Web of Science to assess the origin of MP in soil and crops and its effects on soil organisms, plants, and humans. It was observed that MPs come from different sources such as waste water, organic fertilizer, irrigation water, sewage, and sludge. Plastic mulching, which can spread across agricultural fields at varying depths, is the dominant source. Furthermore, it was observed that MPs alter crop quality, reduce the leaf count of wheat, and decrease the root length of crops such as maize, water spinach, black gram, and garden cress. MP can decrease the abundance of soil microarthropods and nematodes, damage the intestinal walls of earthworms, and reduce the feeding and excretion of snails. MP causes liver damage, inflammation, respiratory irritation, and immunological issues. Ultimately, these contaminants (MPs) can transfer and have been detected in fruits and vegetables, which pose adverse effects on human health.

Gully erosion on agricultural land severely damages land resources and affects agricultural production. Topographic features, tillage methods, and roads are major elements constituting the farmland landscape, but the effect of their distribution in the farmland on the gully erosion is still unclear. This study examined the long-term impacts of changes in the farmland environment and climate change on gully erosion over a long temporal scale of nearly 60 years, the results showed that farmland reclamation over the past 60 years had led to a 2324.2 % increase in gully length density and a 3563.3 % increase in gully area density. The increase in annual rainfall amount and the frequency of extreme rainstorms had led to a rapid increase of gully erosion intensity in the last decade, with an average development rate in length density and area density of 61.5 m km- 2 and 778.7 m2 km- 2, respectively. Farmlands with slope aspects between 135 and 270 degrees were more prone to gully erosion, which was related to the redistribution of snow on hillslopes caused by prevailing wind directions. Tillage methods and roads simultaneously affect gully erosion, with newly formed gullies located in farmlands and roadsides accounting for 63.0 % and 29.8 %. Gullies in regions where the angle between furrows and unpaved roads exceeded 70 degrees accounted for 61.1 % of the total roadside gullies. Over the last decade, the annual average increase of gully length and area was 9.8 m yr-1 and 246.1 m2 yr-1. The development rate of gully area was significantly correlated with the drainage area.

Heavy metal pollution can have adverse impacts on microorganisms, plants and even human health. To date, the impact of heavy metals on bacteria in farmland has yielded poor attention, and there is a paucity of knowledge on the impact of land type on bacteria in mining area with heavy metal pollution. Around a metal-contaminated mining area, two soil depths in three types of farmlands were selected to explore the composition and function of bacteria and their correlations with the types and contents of heavy metals. The compositions and functions of bacterial communities at the three different agricultural sites were disparate to a certain extent. Some metabolic functions of bacterial community in the paddy field were up-regulated compared with those at other site. These results observed around mining area were different from those previously reported in conventional farmlands. In addition, bacterial community composition in the top soils was relatively complex, while in the deep soils it became more unitary and extracellular functional genes got enriched. Meanwhile, heavy metal pollution may stimulate the enrichment of certain bacteria to protect plants from damage. This finding may aid in understanding the indirect effect of metal contamination on plants and thus putting forward feasible strategies for the remediation of metal-contaminated sites. Main findings of the work: This was the first study to comprehensively explore the influence of heavy metal pollution on the soil bacterial communities and metabolic potentials in different agricultural land types and soil depths around a mining area.

Soil surface roughness (SSR) is an important indicator that characterizes the microtopography feature of farmland after tillage. It has a high practical value for sowing and seedling raising, farmland management, and drainage irrigation in agricultural production. The traditional method often is prone to damage the surface microstructure and results in low efficiency and accuracy. In this study, a new method was proposed to address the limitations of traditional measurement methods of SSR. The proposed measurement and evaluation method of farmland microtopography feature information based on 3D lidar and inertial measurement unit (IMU) could be used to quickly obtain the global point cloud map containing the height data of the test field. Taking three different tillage methods of farmland as the research object, the surface root mean square height (RMSH), correlation length (CL), and their ratio were selected as roughness parameters to explore the anisotropy of microtopography features in different directions. The measurement method was then used to study the effects of sampling processing methods (number, interval, and length) on the measurement accuracy in both OX and OY directions. The results indicate that under the same accuracy requirements, for the 2 x 2 m area, the farmland with different microtopography features needs to be processed with different sample numbers, sample intervals, and sample lengths. The optimal combination of sample parameters for Test field I is sample number of 50, sample interval of 120 mm, and sample interval of 1600 mm, and that in Test field II is sample number of 50, sample interval of 160 mm, and sample interval of 1800 mm. For Test field III, the optimal combination is sample number of 100, sample interval of 40 mm, and sample length of 1200 mm. The experimental results compared with the traditional method illustrate the high accuracy and good feasibility of the proposed method for measuring and evaluating the microtopography feature information of the farmland. The results of the study help to understand the microtopography features and its parameterization of the farmland after tillage, which could further reveal the role and significance of SSR parameters in objectively evaluating farmland tillage quality and optimizing farmland management.

Wetlands play a crucial role in oxygen production, air purification, and quality maintenance. Thus, conservation of wetland is essential in response to natural and anthropogenic damaging activities. Restored farmland, utilized to repair the southern buffer zone of Jiangsu Yancheng Wetland National Nature Reserve for Rare Birds, was used to investigate and analyze the diversity of migratory birds and soil fauna. In this study, five different crops, colza oil, mustard, Chinese cabbage, wheat, and barley, were planted in the restored plots, which were foraged by overwintering migratory birds, resulting in low crop yield. The soil fauna biodiversity and biomass in the wheat, Chinese cabbage, and colza oil plots during winter were relatively rich, which attracted many migratory birds to roost and feed. The variability and population of migratory birds significantly improved (18 species and 164231 migratory birds), which was owed to soil fauna and planted crops. Therefore, based on the results of our study, farmland restoration could significantly enrich the biodiversity of soil fauna and migratory birds, improve the ecological environment of wetlands, and attract more migratory birds as inhabitants.

Vegetation cover has implications for seasonally frozen soil dynamics and greenhouse gas emissions. We examined the frozen soil dynamics and N2O and CO2 efflux in a forest plantation (Populus ssp.) and farmland. The experiments were carried out at a forest reclamation site in Zhangbei county, Hebei province, China, from November 2017 to May 2018. Compared to the farmland, the forest plantation prolonged the retention of frozen soil because the shallower snow and the longer duration of snow cover in the forest contributed to a deeper frost depth and delayed soil thawing. The canopy also sheltered the frozen soil from the extreme fluctuations in freeze-thaw cycles (FTCs) during the snow-free period. Contrasting snow regimes and FTC dynamics contributed to variations in CO2 and N2O between the forest plantation and the farmland. Path analysis showed that the soil water content and soil temperature were the main regulators of N2O and CO2 emissions, respectively, in both land-use types. By contrast, soil substrate and microorganism biomass minimally influenced N2O and CO2 efflux. In conclusion, forest cover influences frozen soil dynamics and greenhouse gas emissions by buffering temperature fluctuations in both snow-covered and snow-free periods. This study further highlights the potential importance of anthropogenic land-use changes in influencing the cold season energy balance and gas efflux in future milder winter climates. (C) 2020 Elsevier B.V. All rights reserved.