Phthalates and other organic chemicals in agricultural soils after use of different types of conventional and biodegradable plastics.

Various plastic materials are used in contact with agricultural soil, like mulching films, crop covers, weed controlling fabrics and nets. Polyethylene (PE) mulches have already been recognized as a significant source of plastic in soil and they have been shown to contain additives like phthalates, known as endocrine disruptors. However, other agricultural plastics are less studied, and little is known on the substances potentially released from them endangering biodiversity and the human health. This research aims to assess whether different agricultural plastics release additives into soil and to compare the release among various materials. We collected soil samples from 38 agricultural fields where conventional mulching films (PE), weed controlling fabrics (PP), biodegradable mulches based on polybutylene adipate terephthalate (PBAT), frost covers (PP), and oxo-degradable films (at least OXO-PE) were used. We analyzed the soils for phthalates and acetyl tributyl citrate (ATBC), used as plastic additives, and for polycyclic aromatic hydrocarbons (PAH) and dodecane that have high affinity for plastics. In comparison to the control soils, dibutylphthalate (DBP) and ATBC concentrations were significantly higher in soils mulched with PE and, partly, with biodegradable films. DBP concentration found in soil samples ranged between below the limit of quantification at a control site (1.5 µg kg-1) to 135 µg kg-1 at a site mulched with OXO-PE. The highest ATBC concentration, 22 ± 6 µg kg-1, was registered in a site mulched with PE, showing a statistically significant difference not only in comparison to the controls but also when compared to sites mulched with OXO-PE (p = 0.029) and PBAT (p < 0.009). On the contrary, the use of agricultural plastics did not influence the concentration of PAHs and dodecane. Our results indicate that agricultural plastics are a source of some organic chemicals to agricultural soils, including phthalates that are known for posing threat to soil ecosystem and human health.

Plastic film mulching application improves potato yields, reduces ammonia emissions, but boosts the greenhouse gas emissions in China.

With global population growth and climate change, food security and global warming have emerged as two major challenges to agricultural development. Plastic film mulching (PM) has long been used to improve yields in rain-fed agricultural systems, but few studies have focused on soil gas emissions from mulched rainfed potatoes on a long-term and regional scale. This study integrated field data with the Denitrification-Decomposition (DNDC) model to evaluate the impacts of PM on potato yields, greenhouse gas (GHG) and ammonia (NH3) emissions in rainfed agricultural systems in China. We found that PM increased potato yield by 39.7 % (1505 kg ha-1), carbon dioxide (CO2) emissions by 15.4 % (123 kg CO2 eq ha-1), nitrous oxide (N2O) emissions by 47.8 % (1016 kg CO2 eq ha-1), and global warming potential (GWP) by 38.9 % (1030 kg CO2 eq ha-1), while NH3 volatilization decreased by 33.9 % (8.4 kg NH3 ha-1), and methane (CH4) emissions were little changed compared to CK. Specifically, the yield after PM significantly increased in South China (SC), North China (NC), and Northwest China (NWC), with increases of 66.1 % (2429 kg ha-1), 44.1 % (1173 kg ha-1), and 43.6 % (956 kg ha-1) compared to CK, respectively. The increase in GWP and greenhouse gas emission intensity (GHGI) under PM was more pronounced in the Northeast China (NEC) and NWC regions, with respective increases of 57.1 % and 60.2 % in GWP, 16.9 % and 10.3 % in GHGI. While in the Middle and Lower reaches of the Yangtze River (MLYR) and SC, PM decreased GHGI with 10.2 % and 31.1 %, respectively. PM significantly reduced NH3 emissions in all regions and these reductions were most significant in Southwest China (SWC), SCand MLYR, which were 41 %, 38.0 %, and 38.0 % lower than CK, respectively. In addition, climatic and edaphic variables were the main contributors to GHG and NH3 emissions. In conclusion, it is appropriate to promote the use of PM in the MLYR and SC regions, because of the ability to increase yields while reducing environmental impacts (lower GHGI and NH3 emissions). The findings provide a theoretical basis for sustainable agricultural production of PM potatoes.

Long-term maintenance of high yield and soil fertility with integrated soil-crop system management on the Loess Plateau.

Ridge-furrow with full film mulching has been widely applied to increase crop yield and water productivity on the Loess Plateau, but it may stimulate carbon (C) mineralization. How to integrate other technological benefits based on this technology for long-term maintenance of high yield and soil fertility is a pressing issue. With the local farmers' practice (FP) as a control, three integrated soil-crop system management (ISSM) practices integrating fertilizer rates, fertilizer types and planting densities (ISSM-N1, ISSM-N2 and ISSM-MN) were established to improve maize yield and soil quality. Compared with the FP, the maize yield increased by 13.34%, 21.83% and 30.24%, and the soil quality index (SQI) increased by 9.66%, 14.91% and 38.38% for ISSM-N1, ISSM-N2 and ISSM-MN, respectively. However, ISSM-N1 did not significantly increase yield, and ISSM-N2 increased residual soil nitrate and decreased nitrogen (N) partial factor productivity significantly. Compared to the FP, ISSM practices increased soil organic carbon (SOC), labile organic C fractions (LOCFs) and potassium permanganate organic C fractions in the topsoil to varying degrees, but only ISSM-MN reached significant levels for most C fractions. The sensitivity index indicated very easily oxidizable C (24.6%), easily oxidizable C (24.7%), hot-water extractable C (30.8%), labile organic C (24.7%) and particulate organic C (57.3%) were more sensitive than SOC (22.7%). ISSM-MN sequestered significantly higher C than the other treatments. The results of the relative importance analysis and the structural equation model indicated that LOCFs were the direct contributors to yield, while recalcitrant C (CO) was the indirect contributor, revealing the underlying mechanism that CO decomposed to replenish LOCFs and the total N pool with the water soluble C pool as the transit station. Overall, ISSM-MN is the most promising strategy to improve crop yield and soil fertility in the long term on the Loess Plateau.

Microplastics - Back to Reality: Impact of Pristine and Aged Microplastics in Soil on Earthworm Eisenia fetida under Environmentally Relevant Conditions.

Recently, studies have highlighted the potential danger for soil organisms posed by film-derived microplastics (MPs). However, the majority of those does not accurately reflect the field conditions and the degree of MP contamination that can be found in actual settings. To fill the gap between laboratory and field scenarios, the polyethylene (PE) plastic film was made into PE-MPs and aged. Toxicity and molecular mechanisms of pristine PE-MPs (PMPs) and aged PE-MPs (AMPs) with the concentration at 500 mg/kg of dry weight were determined after 14 days of exposure by measuring the oxidative stress, osmoregulation pressure, gut microbiota, and metabolic responses in earthworms under environmentally relevant conditions. Our research showed that, when compared to PMPs (13.13 ± 1.99 items/g), AMPs accumulated more (16.19 ± 8.47 items/g), caused more severe tissue lesions, and caused a higher increase of cell membrane osmotic pressure in earthworms' intestines. Furthermore, the proportion of probiotic bacteria Lactobacillus johnsonii in the gut bacterial communities was 24.26%, 23.26%, and 12.96%, while the proportion of pathogenic bacteria of the phylum Verrucomicrobia was 2.28%, 4.79%, and 10.39% in the control and PMP- and AMP-exposed earthworms, indicating that the decrease in number of probiotic bacteria and the increase in number of pathogenic bacteria were more pronounced in the gut of AMP- rather than PMP-exposed earthworms. Metabolomic analysis showed that AMP exposure reduced earthworm energy metabolites. Consequently, the constant need for energy may result in protein catabolism, which raises levels of some amino acids, disturbs normal cell homeostasis, causes changes of cell membrane osmolarity, and destroys the cell structure. Our studies showed that aged MPs, with the same characteristics as those found in the environment, have greater toxicity than pristine MPs. The results of this study broaden our understanding of the toxicological effects of MPs on soil organisms under environmentally relevant conditions.

Effect of Mulching on Soil Temperatures and Its Impact on Plasmodiophora brassicae and Clubroot.

Clubroot caused by Plasmodiophora brassicae is a serious soilborne disease on cruciferous crops worldwide. Agricultural practice is a preferable clubroot management strategy because of its low investment requirement and environmental safety. Among the agricultural practices, solarization has been widely applied in the integrated management of other soilborne diseases. However, only few reports exist on the effect of solarization on clubroot management. In this study, we measured the effect of plastic mulching on soil temperature at different depths and on clubroot incidence and severity under greenhouse and field conditions. The pathogen density in the soil after solarization was measured by quantitative PCR analysis. Results indicated that the mulching treatment increased soil temperature especially in the soil layer ranges of 0 to 20 cm. Solarization with mulching also effectively reduced the incidence and severity of clubroot in the greenhouse assay and the field trial by decreasing the P. brassicae population in the soil. This study suggested that solarization with mulching can impair clubroot development and thus contribute to the sustainable management of clubroot.

Abundance, spatial distribution, and characteristics of microplastics in agricultural soils and their relationship with contributing factors.

Agro-ecosystem contamination with microplastics (MPs) is of great concern. However, limited research has been conducted on the agricultural soil of tropical regions. This paper investigated MPs in the agro-ecosystem of Hainan Island, China, as well as their relationships with plastic mulching, farming practices, and social and environmental factors. The concentration of MPs in the study area ranged from 2800 to 82500 particles/kg with a mean concentration of 15461.52 particles/kg. MPs with sizes between 20 and 200 µm had the highest abundance of 57.57%, fragment (58.16%) was the most predominant shape, while black (77.76%) was the most abundant MP colour. Polyethylene (PE) (71.04%) and polypropylene (PP) (19.83%) were the main types of polymers. The mean abundance of MPs was significantly positively correlated (p < 0.01) with all sizes, temperature, and shapes except fibre, while weakly positively correlated with the population (p = 0.21), GDP (p = 0.33), and annual precipitation (p = 0.66). In conclusion, plastic mulching contributed to significant contamination of soil MPs in the study area, while environmental and social factors promoted soil MPs fragmentation. The current study results indicate serious contamination with MPs, which poses a concern regarding ecological and environmental safety.

How much does it cost to mitigate soil erosion after wildfires?

Wildfires usually increase the hydrological and erosive response of forest areas, carrying high environmental, human, cultural, and financial on- and off-site effects. Post-fire soil erosion control measures have been proven effective at mitigating such responses, especially at the slope scale, but there is a knowledge gap as to how cost-effective these treatments are. In this work, we review the effectiveness of post-fire soil erosion mitigation treatments at reducing erosion rates over the first post-fire year and provide their application costs. This allowed assessing the treatments' cost-effectiveness (CE), expressed as the cost of preventing 1 Mg of soil loss. This assessment involved a total of 63 field study cases, extracted from 26 publications from the USA, Spain, Portugal, and Canada, and focused on the role of treatment types and materials, and countries. Treatments providing a protective ground cover showed the best median CE (895 $ Mg-1), especially agricultural straw mulch (309 $ Mg-1), followed by wood-residue mulch (940 $ Mg-1) and hydromulch (2332 $ Mg-1). Barriers showed a relatively low CE (1386 $ Mg-1), due to their reduced effectiveness and elevated implementation costs. Seeding showed a good CE (260 $ Mg-1), but this reflected its low costs rather than its effectiveness to reduce soil erosion. The present results confirmed that post-fire soil erosion mitigation treatments are cost-effective as long as they are applied in areas where the post-fire erosion rates exceed the tolerable erosion rate thresholds (>1 Mg-1 ha-1 y-1) and are less costly than the loss of on- and off-site values that they are targeted to protect. For this reason, the proper assessment of post-fire soil erosion risk is vital to ensure that the available financial, human and material resources are applied appropriately.

Effects of mulching types on the yield and water utilization by broomcorn millet (Panicum miliaceum): Results of a study in the Loess Plateau, China.

Mulching practices have been widely adopted to improve rainfed crop productivity. However, the major resources including water, heat, and light that influenced the yield of broomcorn millet in different dryland regions have rarely been explored. A three-season field experiment with three mulching practices i.e. traditional planting with non-mulching (TP), ridge-furrow mulching system (RF), and plastic film mulching (PFM) was conducted in three semi-arid regions in the Loess Plateau, China, i.e. Guyuan city (GY), Huining county (HN), and Yulin city (YL) between 2020 and 2022 to investigate the impacts of mulching regimes on soil hydrothermal conditions, agronomic characteristics, leaf photosynthetic properties, broomcorn millet yield, and water use efficiency (WUE). Results showed that both PFM and RF treatments increased soil temperature and moisture, and enhanced dry matter accumulation by promoting leaf photosynthetic capacity and chlorophyll content, thereby improving broomcorn millet yield and WUE. PFM and RF increased the average broomcorn millet yield by 15.08% and 24.86% at GY site, 20.86% and 25.61% at HN site, and 15.75% and 25.57% at YL site, respectively, and increased the average WUE by 16.31% and 27.48% at GY site, 23.21% and 28.80% at HN site, 15.55% and 28.57% at YL site, respectively. Partial least squares path modeling analysis revealed that soil moisture was an important environmental factor in determining broomcorn millet yield. Overall, RF practice can be taken to improve the management of agricultural climate factors and maximize yield, thereby promoting the sustainable development of dryland agriculture in the Loess Plateau.

Is adding biochar be better than crop straw for improving soil aggregates stability and organic carbon contents in film mulched fields in semiarid regions? -Evidence of 5-year field experiment.

Plastic film mulching is used widely to increase crop yields in semiarid areas, but improving the soil fertility in film mulched fields is also important for achieving sustainable high yields in northwest of China. In this study, a completely randomized two-factor field design experiment was conducted in Pengyang, Ningxia, China during 2017-2021. In order to investigate the effects of plastic film mulching with straw/biochar addition on the soil aggregate characteristics, organic carbon content, and maize yield. Six treatments were established as follows: control (C), straw (S), biochar (B), plastic film mulching (F), plastic film mulching with added straw (FS) or biochar (FB). After 5 years of continuous production, each straw and biochar addition treatments significantly improved the soil aggregate distribution and stability, and the average aggregate content >0.25 mm increased significantly by 47.32%. Compared with the treatments without plastic film mulching, the mean weight diameter and geometric mean diameter of the soil particles increased by 9.19% and 4.15%, respectively, under the plastic film mulching treatments. The organic carbon content of the 0-60 cm soil layer increased significantly under each straw and biochar addition treatment compared with the without straw. The aggregate organic carbon contents under each treatment increased as the aggregate particle size increased, where the straw and biochar addition treatments significantly increased the organic carbon content of the aggregates, whereas the contents decreased under the plastic film mulching treatments. The contributions of the soil aggregates >0.25 mm to the organic carbon contents of the 0-60 cm soil layer were significantly higher under FS (37.63%) and FB (56.45%) than F. Structural equation modeling showed that straw/biochar added, plastic film mulching, and a greater soil organic carbon content could significantly promote yield increases, where the straw and biochar addition treatments significantly increased the average maize by 14.6% on average. In conclusion, carbon input as straw, especially biochar, had a positive effect on improving the soil organic carbon content and maize yield under plastic film mulching farmland in a semiarid region.

Costs of preventing and supressing wildfires in Victoria, Australia.

Land managers around the world are increasingly under pressure to demonstrate that the actions being used to moderate wildfire risk are effective and cost-efficient. However, little research to date has focused on determining cost-efficiency of management actions or identified the factors which increase the costs of performing such actions. Here, we aimed to identify the key drivers of cost for fuel management (prescribed burning, mulching, and slashing), fuel breaks, and suppression using data from the state of Victoria, Australia. We utilise generalised additive models to understand how environmental factors, terrain, location, and management decisions influence the cost of implementing wildfire management efforts. These models show that cost per unit declines as the area treated or the area of the fire increases for all four management approaches. Therefore, preventative, and responsive management actions represent economies of scale that reduce in cost with larger treatments. We also found that there were regional differences in the cost of fuel management and fuel breaks, potentially related to the structure of resourcing treatments in each region and the availability of land on which it is feasible to implement management. Cost of suppression per fire increased with the number of fire fighters and when there were more fires occurring concurrently in the landscape. Identifying the key drivers of cost for preventative and responsive management actions could enable managers to allocate resources to these actions more efficiently in future. Understanding drivers of cost-efficiency could be critical for adapting management to shifts in wildfire risk, particularly given climate change will alter the window in which it is safe to apply some preventative fuel management actions and reduce suppression effectiveness.

Effects of tillage patterns and stover mulching on N2O production, nitrogen cycling genes and microbial dynamics in black soil.

Stover-covered no-tillage (NT) is of great significance to the rational utilization of stover resources and improvement of cultivated land quality, and also has a profound impact on ensuring groundwater, food and ecosystem security. However, the effects of tillage patterns and stover mulching on soil nitrogen turnover remain elusive. Based on the long-term conservation tillage field experiment in the mollisol area of Northeast China since 2007, the shotgun metagenomic sequencing of soils and microcosm incubation were combined with physical and chemical analyses, alkyne inhibition analysis to elucidate the regulatory mechanisms of NT and stover mulching on the farmland soil nitrogen emissions and microbial nitrogen cycling genes. Compared with conventional tillage (CT), NT stover mulching significantly reduced the emission of N2O instead of CO2, especially when 33% mulching was adopted, and correspondingly the nitrate nitrogen of NT33 was higher than that of other mulching amounts. The stover mulching was associated with higher total nitrogen, soil organic carbon and pH. The abundance of AOB (ammonia-oxidizing bacteria)-amoA (ammonia monooxygenase subunit A) was substantially increased by stover mulching, while the abundance of denitrification genes was reduced in most cases. Under alkyne inhibition, the tillage mode, treatment time, gas condition and interactions between them noticeably influenced the N2O emission and nitrogen transformation. In CT, NT0 (no mulching) and NT100 (full mulching), the relative contribution of AOB to N2O production was markedly higher than that of ammonia oxidizing archaea. Different tillage modes were associated with distinct microbial community composition, albeit NT100 was closer to CT than to NT0. Compared with CT, the co-occurrence network of microbial communities was more complex in NT0 and NT100. Our findings suggest that maintaining a low-quantity stover mulching could regulate soil nitrogen turnover toward proficiently enhancing soil health and regenerative agriculture, and coping with global climate change.

Effects of different colors of film mulch on soil temperature and rice growth in a non-flooded condition.

BACKGROUND: Rice cultivation under film mulching with no flooding is widely used as an effective water-saving technology. Different colors of film mulch have different effects on the soil hydrothermal environment and crop growth because of their different optical properties. However, the effects of different colors of film mulch on soil temperature and rice physiological growth are not clearly understood. RESULTS: Field experiments were conducted in 2019 and 2020 to investigate the effects of different color mulches on soil temperature and rice growth in a non-flooded condition. Transparent film (TM), black film (BM), two-color film (BWM, silver on the front and black on the back), and no film (NM) in a non-flooded condition were designed. Soil temperature variation at different soil depths of 0-0.25 m and rice plant height, stem thickness, dry matter, yield and quality were monitored. The results showed that compared to no mulching, the mulching treatment effectively increased the average soil temperature during the whole rice growth stage with the soil temperature ranked TM > BM > BWM. Compared with NM, the BM and BWM treatments increased rice yield by 12.1-17.7% and 6.4-14.4% in 2019 and 2020, respectively. The BWM had 18.2% and 6.8% greater gel consistency than NM in 2019 and 2020, respectively. CONCLUSION: Transparent film should be applied with care because of the high soil temperature stress. Black film and two-color film (silver on the front and black on the back) could be better option for rice yield, increasing and quality improving in a non-flooded condition. © 2023 Society of Chemical Industry.

Timing and water temperature of drip irrigation regulate cotton growth and yield under film mulching in arid areas of Xinjiang.

BACKGROUND: Cotton (Gossypium hirsutum L.) is the fiber crop most widely cultivated globally and one of the most important commercial crops in China, irrigation is closely related to the growth of cotton. A water temperature for irrigation that is too low or too high inhibits cotton growth. Poor irrigation timing results in water and nutrient deficiencies that reduce cotton yield. Therefore, it is necessary to determine the appropriate irrigation timing and water temperature. METHOD: We conducted an experiment in an arid region of north-western China to assess the effects of irrigation timing and water temperature on soil temperature and the photosynthetic characteristics, biomass, total nitrogen (N), and seed cotton yield. Two irrigation times (daytime and nighttime) and four water temperatures (15, 20, 25, and 30 °C) were combined into eight treatments. RESULTS: Our results showed that water warming and nighttime irrigation improved the photosynthesis, biomass, N concentration (the proportion of total N weight in the plant biomass, in g kg-1 ), N content (the mass of total N, in g plant-1 ), and cotton yield. The optimal water temperature range for photosynthesis was 25.7-28.7 °C. Water warming also boosted the biomass allocation to the stem and increased the N allocation to the stem and leaf. Nighttime irrigation enhanced these phenomena. Water warming also increased the number of bolls per plant but reduced the single boll weight, increasing the seed cotton yield by 5.88-11.46%. At the same water temperature, irrigation during the night increased the number of bolls per plant and the single boll weight, improving the seed cotton yield by 2.95-4.31%. Among them, NI25 (nighttime irrigation with 25 °C water temperature) increased the yield by 14.13-14.90% compared with CK (daytime irrigation with 15 °C water temperature), which offers the best combination for increasing the yield. CONCLUSION: Our study clarifies the optimal irrigation timing and water temperature for cotton production under drip irrigation with film mulching, providing valuable information for improving the cotton yield in arid areas with temperate continental climate. © 2023 Society of Chemical Industry.

Spatial Distributions, Compositional Profiles, Potential Sources, and Intfluencing Factors of Microplastics in Soils from Different Agricultural Farmlands in China: A National Perspective.

More attention has been paid to ubiquitous microplastics (MPs). As a major food producer, the situation of MPs in China's farmland is of even greater concern. Spatial distributions, characteristics, and compositions of MPs in five types of agricultural lands with representative crops were investigated by collecting 477 soil samples from 109 cities in 31 administrative regions of mainland China. To better control MPs in farmland, nearly 400 field questionnaires were obtained, and meteorological conditions, soil properties, and other statistics were collected to quantify potential sources and determine influencing factors. The average abundances of MPs was 2462 ± 3767 items/kg in the agricultural soils, and MP abundance in the greenhouses, farmlands with film mulching, and blank farmlands from four integrated physical geographic regions were determined. The contributions of agricultural films, livestock and poultry manures, irrigation water, and air deposition to MPs in farmlands have been calculated. Influencing factors, such as recovery method, plowing frequency, meteorological conditions, and part of soil properties, were significantly correlated with the abundances of MPs in the agricultural soils (p < 0.05), while mulching age mainly affected MPs in the greenhouses (p < 0.05). This study provides basic scientific data for decision-making and further analysis.

A novel process for food waste recycling: A hydrophobic liquid mulching film preparation.

Appropriate and effective recycling of food waste (FW) has become increasingly significant with the promotion of garbage classification in China. In this study, a novel and green process was developed to recycle FW to prepare a biodegradable composite liquid mulching film (LMF) through crosslinking with sodium alginate (SA). The solid phase of FW was obtained as the raw material after hydrothermal pretreatment to remove pathogens and salts, and to improve the reactivity of active components at a moderate temperature. The prepared LMF had a hydrophobic surface and compact structure due to the lipid in FW and the acetalization reaction and hydrogen bonds among SA, glutaraldehyde and multi-active components of FW, resulting in enhanced water vapor barrier properties. The minimum water vapor permeability of the prepared LMF reached (8.23 ± 0.05) ✕ 10-12 g cm/(cm2·s·Pa) with 1.82 wt % of plasticizer, 0.74 wt% of crosslinker and a mass ratio of HTP-FW to SA of 3.56:1. The prepared LMF showed good mechanical properties and could maintain its integrity after spraying it on the soil surface for 31 days. In addition, it could effectively prevent the loss of soil moisture and heat, promote the seed germination of Chinese cabbage and achieve 89.14% of weight loss after burying in the soil for 27 days. This study provides a high value-added route to convert the FW to a hydrophobic LMF with superior properties, which addresses not only the problem of food waste but also the pollution of plastic mulching film.

What will polyethylene film mulching bring to the root-associated microbial community of Paeonia ostii?

Plastic film mulching can increase crop yield and is widely used in agricultural production, but long-term mulching could adversely affect plant growth. To investigate the related mechanism, we studied the bacterial communities in different root-associated compartments of Paeonia ostii, a perennial oil crop, under polyethylene film mulching for three years by full-length 16S rDNA sequencing technology, and measured the soil physicochemical properties and enzyme activities. We found that enzyme activities and available nutrients in the soil tended to decrease after long-term mulching. Analysis of bacterial community composition revealed that the endosphere may be another potential source of the root-associated microbiome of P. ostii, and the rhizoplane plays a selective gating role in the enrichment processes for P. ostii microbiome assembly. Long-term mulching affected the abundance of dominant bacterial communities in different root-associated compartments and reduced the bacterial richness in the endosphere, but increased bacterial interactions in each compartment, as well as between different compartments. We speculate that this is mainly related to the decrease of litter content and the serious degradation of polyethylene film after long-term mulching, which resulted in microplastics and other harmful substances entering the soil. Our study further explained the reasons for the harm of long-term film mulching on plants to guide the rational use of plastic film. KEY POINTS: •Soil enzyme activities and available nutrients decreased after long-term mulching. •Mulching affected the dominant bacterial abundance in different root-associated compartments. •Mulching increased bacterial interactions among compartments.

Effects of different colored polyethylene mulching films on bacterial communities from soil during enrichment incubation.

Studies have shown that mulching agricultural fields with plastic residues can influence microbial communities in the environment, but few studies have investigated the differences in the soil microbial communities in distinct areas under mulching with different colored plastic products. Thus, in this study, we explored how different colored polyethylene mulching films (PMFs) might affect soil bacterial communities during enrichment incubation. We found significant differences in the bacterial communities under different colored PMFs after incubation. Treatment with the same colored PMF obtained more similar bacterial community compositions. For instance, at the class level, Gammaproteobacteria and Bacteroidia were most abundant with black PMF, whereas Actinobacteria and Bacteroidia were most abundant with white PMF. The most abundant genera were Acinetobacter and Chryseobacterium with black PMF but Rhodanobacter and Paenarthrobacter with white PMF. Polyethylene- and hydrocarbon-degrading bacteria were the core members detected under both treatments, and the bacterial communities were predicted to have the potential for the biodegradation and metabolism of xenobiotics after enrichment culture according to the Phylogenetic Investigation of Communities by Reconstruction of Unobserved States (PICRUSt) tool. In addition, the bacterial communities in soil from Xinjiang treated with white PMF and in soil from Yangling treated with black PMF were strongly correlated and stable. Our results suggest that the color of the PMF applied affected the soil bacterial communities, where plastics with the same color may have recruited similar species of microorganisms, although the origins of these microorganisms were not the same.

Restoring soil carbon in marginal land of Indian Himalayas: Impact of crop intensification and conservation tillage.

Soil carbon (C) loss is the prime sign of land degradation, and C pools have a great impact on soil quality and climate change mitigation. Hence, a field experiment was conducted for three consecutive years to assess the impact of crop intensification and conservation tillage practices on changes in the C pool at different soil depths of marginal land of the Indian Himalayas. The experiment consisted of two intensified cropping systems viz., CS1-Summer maize (Zea mays L.) -rainy season maize-lentil (Lens esculenta L.) and CS2-Summer maize-rainy season maize-mustard (Brassica juncea (L.) Czern) and five tillage practices viz., No-till (NT); NT + live mulch of cowpea (NT + LMC); reduced tillage (RT); RT + LMC and conventional tillage (CT). Results revealed that CS2 produced significantly higher biomass, C retention efficiency (9.85%), and sequestrated greater C (0.42 Mg ha-1 yr-1) in the soil system than CS1. Of the various tillage practices, RT + LMC registered higher biomass and recycled greater biomass and C than those under other tillage practices. However, the highest soil organic carbon (SOC) content (7.03 g kg-1) and pool (9.62 Mg ha-1) in 0-10 cm depth were observed under NT + LMC. The non-labile C pool size under NT in 0-10 cm and 10-20 cm depths was significantly greater than those under CT. The NT + LMC sequestrated significantly higher SOC (0.57 Mg ha-1 yr-1) than other tillage practices. Thus, the study indicated that the adoption of an intensified maize-based system under RT + LMC or NT + LMC would increase SOC storage and C sequestration in marginal lands of the Indian Himalayas.

Winter drainage and film mulching cultivation mitigated CH4 emission by regulating the function and structure of methanogenic archaeal and fermenting bacterial communities in paddy soil.

Winter flooding of harvested rice fields is a typical cropping system in mountainous areas, which emits considerable amounts of CH4. Plastic film mulching cultivation is recognized as an important rice cultivation practice in paddy field for water-saving irrigation. However, the effects of these managements on CH4 emissions in paddy soil and the underlying microbial mechanism are unclear. A field experiment was carried out with the application of winter drainage followed by traditional rice cultivation (WD), winter drainage followed by plastic film mulching cultivation (MC), as well as winter flooding followed by traditional rice cultivation (WF) as control in hilly paddy fields. We investigated the CH4 emissions, functional (CH4 production rate, 13C isotope) and structural (abundance, structure) responses of soil methanogenic archaeal and fermenting bacterial communities during rice season. Shifting the fields from WF into WD and MC substantially mitigated CH4 emissions by 62.3% and 59.2%, respectively, paralleled with the enhancement of soil Eh and the reductions of soil DOC content. Compared with WF, WD and MC both significantly decreased CH4 production rates and the copy numbers of mcrA gene. Moreover, an increasing contribution of hydrogenotrophic methanogenesis (from 30.7% to 50.0%) to total CH4 production was observed during the conversion from WF to MC under an anaerobic incubation, paralleled with the decreased acetate content and increased δ13C values of acetate-methyl and total acetate. The communities of methanogenic archaea and fermenting bacteria strongly responded to the shift from WF to WD, while MC only showed significant effects on the methanogenic archaeal communities. Compared with WF, WD and MC significantly increased the relative abundance of Methanothrix, Methanosarcina and Methanocella, while those of Methanoregula, Massilia and Geobacter were decreased. The co-occurrence networks showed that WD and MC induced the loss of mixed methanogenic fermentation modules, indicating the decrease in functional biodiversity and redundancy of fermenting bacterial and methanogenic archaeal communities.The findings suggest that WD and MC approach mitigate CH4 emission by regulating the function and structure of methanogenic archaeal and fermenting bacterial communities in paddy soil, which represent the effective management strategies considering the water availability and CH4 mitigation in paddy-field agriculture.

Upgrading Solid Digestate from Anaerobic Digestion of Agricultural Waste as Performance Enhancer for Starch-Based Mulching Biofilm.

Developing a green and sustainable method to upgrade biogas wastes into high value-added products is attracting more and more public attention. The application of solid residues as a performance enhancer in the manufacture of biofilms is a prospective way to replace conventional plastic based on fossil fuel. In this work, solid digestates from the anaerobic digestion of agricultural wastes, such as straw, cattle and chicken manures, were pretreated by an ultrasonic thermo-alkaline treatment to remove the nonfunctional compositions and then incorporated in plasticized starch paste to prepare mulching biofilms by the solution casting method. The results indicated that solid digestate particles dispersed homogenously in the starch matrix and gradually aggregated under the action of a hydrogen bond, leading to a transformation of the composites to a high crystalline structure. Consequently, the composite biofilm showed a higher tensile strength, elastic modulus, glass transition temperature and degradation temperature compared to the pure starch-based film. The light, water and GHG (greenhouse gas) barrier properties of the biofilm were also reinforced by the addition of solid digestates, performing well in sustaining the soil quality and minimizing N2O or CH4 emissions. As such, recycling solid digestates into a biodegradable plastic substitute not only creates a new business opportunity by producing high-performance biofilms but also reduces the environmental risk caused by biogas waste and plastics pollution.