Mitigation of greenhouse gas emissions and improved yield by plastic mulching in rice production

Soil mulching technologies are effective practices which alleviate non-point source pollution and carbon emissions, while ensuring grain production security and increasing water productivity. However, the lack of comprehensive understanding of the impacts of mulching technologies on rice fields has hindered progress in global implementation due to the varying environments and application conditions under which they are implemented. This study conducted a meta-analysis based on 2412 groups of field experiment data from 313 studies to evaluate the effects of soil mulching methods on rice production, greenhouse gas (GHG) emissions and water use efficiency. The results show that plastic mulching, straw mulching and no mulching (PM, SM and NM) have reduced CH₄ emissions (68.8 %, 61.4 % and 57.2 %), increased N₂O emissions (84.8 %, 89.1 % and 96.6 %), reduced global warming potentials (50.7 %, 47.5 % and 46.8 %) and improved water use efficiency (50.2 %, 40.9 % and 34.0 %) compared with continuous flooding irrigation. However, PM increased rice yield (1.6 %), while SM and NM decreased yield (4.3 % and 9.2 %). Furthermore, analysis using random forest models revealed that rice yield, GHG emissions and WUE response to soil mulching were related to climate, soil properties, fertilizer and rice varieties. Our findings can guide the implementation of plastic mulching technology in priority areas, contribute to agricultural carbon neutrality and support the development of practical guidelines for farmers.

Spatio-temporal variation of soil microplastics as emerging pollutant after long-term application of plastic mulching and organic compost in apple orchards

Microplastics (MPs) pollution in agroecosystems have aroused great alarm and widespread concern. However, the spatial distribution and temporal variation characteristics of MPs in apple orchards with long-term plastic mulching and organic compost input are still poorly understood. This study investigated MPs accumulation characteristics and vertical distribution after applying plastic mulch and organic compost in apple orchards for 3 (AO-3), 9 (AO-9), 17 (AO-17), and 26 (AO-26) years on the Loess Plateau. The clear tillage (no plastic mulching and organic composts) area was used as a control (CK). At a soil depth of 0-40 cm, AO-3, AO-9, AO-17, and AO-26 treatments increased the abundances of MPs, and the black fibers and fragments of rayon and polypropylene were dominant. In the 0-20 cm soil layer, the abundances of MPs increased with the treatment time; the abundance was 4333 pieces kg^-1 after 26 years of treatment, gradually decreasing with soil depth. In different treatments and soil layers, the percentages of MPs <1000 μm were dominant (>50%). The AO-17 and AO-26 treatments significantly increased the MPs with the size of 0-500 μm at 0-40 cm and the abundances of pellets in 0-60 cm soil. In conclusion, the long-term (≥17 years) application of plastic mulching and organic composts increased the abundances of small particles at 0-40 cm, and plastic mulching contributed the most to MPs, while organic composts increased the complexity and diversity of MPs.

Field management changes the distribution of mesoplastic and macroplastic in Mollisols of Northeast China

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.

The persistently breaking trade-offs of three-decade plastic film mulching: Microplastic pollution, soil degradation and reduced cotton yield

Plastic mulching has been extensively used for near 40 years in China because of the commonly recognized trade-offs between economic profit and adverse impacts. Whether the trade-offs is well kept after decades of mulching usage is poorly understood. In this study, microplastic (MP) pollution, soil physical properties, as well as the root traits and yields of cotton under plastic mulching for different years (up to 32 years) in northwest China were investigated. The results showed that average abundance of MPs in soil ranged from 28.00 to 1426.67 items kg^-1 and increased with time whereas size of MPs decreased with time. With respect to soil physical properties, bulk density and penetration resistance significantly increased with mulching time while saturated hydraulic conductivity and mean weight diameter of water-stable aggregates in cotton fields decreased over time, indicating that long-term plastic mulching has irreversible adverse impact on soil function. The significantly increased soil penetration resistance and decreased hydraulic conductivity substantially restricted root growth and this finally led to remarkable reduction of seed cotton yield. It is urgent for the agricultural departments to take appropriate measures to mitigate the constantly increased negative trade-offs of plastic mulching in the arid areas.

Plastic debris in plastic-mulched soil-a screening study from western Germany

Background

Agricultural plastic mulches offer great benefits such as higher yields and lower pesticide use. Yet, plastic mulches may disintegrate over time and fragment into smaller debris. Such plastic debris is expected to remain in the field after removal of the plastic mulch and thus contributes to soil contamination with plastics.

Method

To investigate this, we collected soil samples at 0-10 cm and 10-40 cm depth from three fields covered with black mulch film for three consecutive years. Three fields without any reported plastic use served as control. Visual plastic debris > 1 cm (macroplastics) was collected from the soil surface. Mesoplastics between 2 mm and 1 cm were density separated from the sampled soil using saturated NaCl solution and analyzed by Fourier-transform infrared spectroscopy. Debris ≤ 2 mm (microplastics) was dispersed from 50 g soil using sodium hexametaphosphate solution followed by the aforementioned density separation. The separated polyethylene (PE), polypropylene (PP), and polystyrene (PS) were quantified via solvent-based pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS).

Results

With 89-206 fragments ha^-1, the majority of macroplastics were located in fields previously covered with mulch films. 80% of the collected specimen were identified as black PE film. The number of mesoplastics in plastic-mulched soil was 2.3 particles kg^-1, while only 1.0 particles kg^-1 were found in the reference fields. Py-GC/MS revealed microplastic levels of up to 13 mg kg^-1. The PE content was significantly higher in plastic-mulched fields than in reference fields.

Discussion

Although the identified plastic levels are lower than those reported in comparable studies, our results still suggest that plastic mulching functions as a source of plastic debris in agricultural systems. Due to its severely restricted degradability, these plastics are likely to accumulate in soil in the long term and further fragment into smaller and smaller debris.

How does multiannual plastic mulching in strawberry cultivation influence soil fungi and mycotoxin occurrence in soil?

The production of mycotoxins is often interpreted as fungal response to cope with unfavorable growth conditions induced by toxic substances, environmental and biological factors. Soil covers influence soil environment, which consequently can change the abundance and composition of microbial communities. We investigated how plastic coverage (PC) influence soil fungi and mycotoxin occurrence (deoxynivalenol, nivalenol and zearalenone) compared to the traditional straw coverage (SC) in dependence of soil depth and time in a 3-year field experiment in strawberry cultivation. In total, 300 soil samples, resulting from two treatments, three soil layers, and ten sampling dates (n = 5), were analyzed for mycotoxins and ergosterol (proxy for soil fungal biomass) with liquid chromatography high resolution mass spectrometry and high-performance liquid chromatography with UV-detection, respectively. The modified microclimate under PC had no significant influence on fungal biomass, whereas SC promoted fungal biomass in the topsoil due to C-input. Mycotoxins were detected under both cover types in concentrations between 0.3 and 21.8 µg kg⁻¹, mainly during strawberry establishment period and after fungicide application. Deoxynivalenol had the highest detection frequency with 26.3% (nivalenol: 8.3%, zearalenone: 8.7%). This study confirmed the in situ production of mycotoxins in soil, which seems mainly triggered by field treatment (fungicide application) and plant growth stage (establishment period) rather than on mulching type. Further investigations are necessary to better understand the influence of different agricultural practices and soil types on the production and fate of mycotoxins.

Effects of microplastics on soil organic carbon and greenhouse gas emissions in the context of straw incorporation: A comparison with different types of soil

Plastic mulching and straw incorporation are common agricultural practices in China. Plastic mulching is suspected to be a significant source of microplastics in terrestrial environments. Straw incorporation has many effects on the storage of soil organic carbon (SOC) and greenhouse gas emissions, but these effects have not been studied in the presence of microplastic pollution. In this study, 365-day soil incubation experiments were conducted to assess the effects of maize straw and polyethylene microplastics on SOC fractions and carbon dioxide (CO₂) and nitrous oxide (N₂O) emissions in two different soils (fluvo-aquic and latosol). Against the background of straw incorporation, microplastics reduced the mineralization and decomposition of SOC, resulting in a microbially available SOC content decrease by 18.9%. In addition, microplastics were carbon-rich, but relatively stable and difficult to be used by microorganisms, thus increasing the mineral-associated SOC content by 52.5%. This indicated that microplastics had adverse effects on microbially available SOC and positive effects on mineral-associated SOC. Microplastics also decreased coarse particulate SOC (>250 μm), and increased non-aggregated silt and clay aggregated SOC (<53 μm). Furthermore, microplastics changed microbial community compositions, thereby reducing the CO₂ and N₂O emissions of straw incorporation by 26.5%-33.9% and 35.4%-39.7%, respectively. These results showed that microplastics partially offset the increase of CO₂ and N₂O emissions induced by straw incorporation. Additionally, the inhibitory effect of microplastics on CO₂ emissions in fluvo-aquic soil was lower than that in latosol soil, whereas the inhibitory effect on N₂O emissions had the opposite trend.

Polyethylene film mulching enhances the microbial carbon-use efficiency, physical and chemical protection of straw-derived carbon in an Entisol of the Loess Plateau

The global use of agricultural polyethylene mulches has emerged as a widespread farming practice, however, its effects on the fate and dynamics of crop straw-derived C in soil microbial biomass C (MBC), aggregate-associated and chemical recalcitrance-related C fractions are rarely assessed in situ. A two-year field experiment using ¹³C-labeled maize stem was carried out to quantify the allocation and dynamics of straw-C in an Entisol with and without plastic mulching. The results indicated that across the treatments, from 49.2% to 56.4% of straw-¹³C was released as CO₂-C, from 34.9% to 43.1% was sequestrated as SOC pool, and from 6.7% to 9.7% remained undecomposed at the end of the experiment. Compared to non-mulching, plastic mulching significantly decreased the straw-derived CO₂-C emissions by 14.6%, partially owing to the increased incorporation of straw-C into SOC pool. Across the treatments, the straw-derived MBC ranged from 14.4 to 147.9 mg ¹³C kg^-1; and plastic mulching increased straw-derived MBC and microbial C use efficiency (CUE) of straw residue by 41.2% and 35.2% compared with non-mulching, respectively. The allocation dynamics of straw-C in each soil aggregate followed a sustained upward trend with time, while a significantly higher straw-C was incorporated into both macro- (> 0.25 mm) and micro-aggregates (0.25-0.053 mm) with plastic mulching. Compared to the non-mulching, plastic mulching enhanced the inclusion of straw-¹³C in the chimerically more stable C fraction, especially at the late experimental period. We conclude that crop straw return combined with plastic mulching could improve SOC sequestration by enhancing microbial CUE, physical and chemical protection of straw-derived C in this dryland cropping system.

Agricultural mulching and fungicides-impacts on fungal biomass, mycotoxin occurrence, and soil organic matter decomposition

Plastic and straw coverage (PC and SC) are often combined with fungicide application but their influence on fungicide entry into soil and the resulting consequences for soil quality are still unknown. The objective of this study was to investigate the impact of PC and SC, combined with fungicide application, on soil residual concentrations of fungicides (fenhexamid, cyprodinil, and fludioxonil), soil fungal biomass, mycotoxin occurrence, and soil organic matter (SOM) decomposition, depending on soil depth (0-10, 10-30, 30-60 cm) and time (1 month prior to fungicide application and respectively 1 week, 5 weeks, and 4 months afterwards). Soil analyses comprised fungicides, fusarium mycotoxins (deoxynivalenol, 15-acetyldeoxynivalenol, nivalenol, and zearalenone), ergosterol, soil microbial carbon and nitrogen, soil organic carbon, dissolved organic carbon, and pH. Fludioxonil and cyprodinil concentrations were higher under SC than under PC 1 week and 5 weeks after fungicide application (up to three times in the topsoil) but no differences were observed anymore after 4 months. Fenhexamid was not detected, presumably because of its fast dissipation in soil. The higher fludioxonil and cyprodinil concentrations under SC strongly reduced the fungal biomass and shifted microbial community towards larger bacterial fraction in the topsoil and enhanced the abundance and concentration of deoxynivalenol and 15-acetyldeoxynivalenol 5 weeks after fungicide application. Independent from the different fungicide concentrations, the decomposition of SOM was temporarily reduced after fungicide application under both coverage types. However, although PC and SC caused different concentrations of fungicide residues in soil, their impact on the investigated soil parameters was minor and transient (< 4 months) and hence not critical for soil quality.

Plastic mulching reduces nitrogen footprint of food crops in China: A meta-analysis

Sustainably feeding the growing population amid rising global temperatures and dwindling resources is a grand challenge facing mankind. Plastic mulching (PM) is widely used in China aiming to the increase of crop productivity. However, the impact of PM on reactive nitrogen (Nr) emissions and nitrogen (N) footprint has not been explicitly described. In this study, we collected 4051 observations from 394 published papers for potato (Solanum tuberosum L.), maize (Zea mays L.), and wheat (Triticum aestivum L.), and used meta-analysis to investigate how PM affected crop yield, net economic return, Nr emissions, and N footprints including nitrogen footprint per unit of output energy (NFo) and nitrogen footprint per unit of net economic return (NFe) at regional scale and across a range of precipitation and N fertilization gradients in China. The meta-analysis showed that compared to non-PM practice, PM increased grain yield by 25, 27, and 20% in potato, maize, and wheat, respectively, and enhanced net economic return by 19, 29, and 22%, respectively, with corresponding reduction in NFo of 24, 36, and 18% and NFe of 19, 37, and 19%, respectively. Potato and maize had greater energy output and net economic return than wheat. Plastic mulching was more effective in improving net economic return (or energy output) and reducing N footprints (i.e., NFe and NFo) in the semiarid region (i.e., annual precipitation <600 mm) when N was applied at 100-200 kg N ha^-1, especially in potato and maize. Our analysis suggests that the use of PM enhanced grain yield and net economic return while lowering the N footprint without increasing Nr emission. Therefore, PM has great potential to mitigate Nr loss in China when crop species, N fertilization rate, and local environmental factors (i.e., growing region and annual precipitation) are appropriately considered.

Microplastics in agricultural soils on the coastal plain of Hangzhou Bay, east China: Multiple sources other than plastic mulching film

Microplastic contamination in agroecosystems raises great concerns. Here, we investigated the impacts of mulching and irrigation on microplastic accumulation in cropped soils. Sixty soil samples covering mulching and no-mulching farmlands, and forty-five irrigation water samples were collected for analysis. Microplastics were obtained from the soils using continuous air flotation followed by density separation. Stereomicroscopy and micro-Fourier transform infrared spectroscopy (μ-FTIR) were used for identification. Mulching soils contained larger amounts of microplastics than non-mulching soils, with 571 pieces kg^-1 and 263 pieces kg^-1, respectively, on average. The abundances of films and fibers were significantly (p < 0.05) higher in the mulching soils. Microplastics in the soils and waters were dominated by fragments and fibers, respectively. The particle size of the microplastics in soils mostly ranged from 1 to 3 mm, and primarily from 90 μm to 1 mm in waters. Multiple polymers, e.g. polyethylene, polypropylene, polyester, rayon, acrylic and polyamide, and shapes found in the soil microplastics indicate contributions from irrigation and plastic waste residues other than plastic mulching. Future studies might include the long-term accumulation of microplastics in agroecosystems from multiple sources under intensively managed cropping systems.

Effect of plastic mulching on mycotoxin occurrence and mycobiome abundance in soil samples from asparagus crops

Plastic mulching (PM) is widely used in modern agriculture because of its advantageous effects on soil temperature and water conservation, factors which strongly influence the microbiology of the soil. The aim of this study was to assess the effect of PM on mycotoxin occurrence in relation with mycobiome abundance/diversity and soil physicochemical properties. Soil samples were collected from green (GA) and white asparagus (WA) crops, the last under PM. Both crops were cultivated in a ridge-furrow-ridge system without irrigation. Samples were analyzed for mycotoxin occurrence via liquid chromatography coupled to high-resolution mass spectrometry (LC-HRMS). Total colony-forming unit was indicative of mycobiome abundance, and analysis of mycobiome diversity was performed by internal transcribed spacer (ITS) sequencing. PM avoided the drop of soil temperature in winter and allowed higher soil temperature in early spring compared to non-covered soil. Moreover, the use of PM provided controlled conditions for water content in soil. This was enough to generate a dissimilar mycotoxin occurrence and mycobiome diversity/abundance in covered and non-covered soil. Mycotoxin soil contamination was confirmed for deoxynivalenol (DON), range LOD to 32.1 ng/g (LOD = 1.1 ng/g). The DON values were higher under PM (average 16.9 ± 10.1 ng/g) than in non-covered soil (9.1 ± 7.9 ng/g); however, this difference was not statically significant (p = 0.09). Mycobiome analysis showed a fungal compartment up to fivefold higher in soil under PM compared to GA. The diversity of the mycobiome varied between crops and also along the soil column, with an important dominance of Fusarium species at the root zone in covered soils.