Biodegradable mulch films improve yield of winter potatoes through effects on soil properties and nutrients.

Biodegradable mulch films are recognized as a promising substitute of polyethylene (PE) films to alleviate the "white pollution". Biodegradable mulch films with optimum degradation rates increase crop yield even compared to PE films. However, the mechanisms underlying this yield-increasing effect remains elusive. In this study, three biodegradable film treatments (BFM1, BFM2 and BFM3) and one PE film treatment (PFM) were used to evaluate their effects on soil and winter potatoes, and a partial least squares path model (PLS-PM) was constructed to investigate their relationships. The degradation rates of films under different treatments were ranked as BFM3 > BFM2 >BFM1 > PFM, and presented distinctive effects on soil properties and nutrients, structure of soil bacterial community, and yield traits of winter potatoes. The PLS-PM showed that mulch treatments affected potato yield through effects on soil properties (soil water and temperature) and soil nutrients (TOC, DOC, TN and NO3--N). The disintegration of the biodegradable films decreased soil water content and temperature, and reduced the loss of soil nutrients in the topsoil at the later growth stage of winter potatoes compared to PE films. Additionally, the elevated content of soil TN and NO3--N under treatment BFM1 may play a key role in its yield-increasing effect on potatoes compared to treatments PFM and BFM2. Thus, biodegradable mulch films with proper degradation rates regulate soil TN and NO3--N through their effects on soil water and temperature, and subsequently improve the yield of winter potatoes compared to PE mulch films.

Partial-film mulch returns the same gains in yield and water use efficiency as full-film mulch with reduced cost and lower pollution: a meta-analysis.

BACKGROUND: Plastic film mulch is widely used to improve crop yield and water use efficiency (WUE, yield per unit evapotranspiration) in semi-arid regions. It is commonly applied as partial-film mulch (PM: at least 50% soil cover) or full-film mulch (FM: complete soil cover). The PM has lower economic and environmental cost; hence it would be a superior technology provided it delivers similar gains in yield and WUE in relation to FM. RESULTS: To solve contradictory results from individual studies, we compared FM and PM in a meta-analysis of 100 studies with 1881 comparisons (685 for wheat; 1196 for maize). Compared with bare ground, FM and PM both increased yield of wheat (20-26%) and maize (37-52%), and WUE of wheat (16-20%) and maize (38-48%), with statistically undistinguishable differences between PM and FM. The increases in crop yield and WUE were stronger at elevation > 1000 m, with annual precipitation<400 mm, and on loess soil, especially for maize. CONCLUSIONS: We concluded that partial-film mulch could replace full-film mulch to return similar yield and WUE improvement, with reduced cost and environmental pollution. © 2021 Society of Chemical Industry.

Effects of the ridge mulched system on soil water and inorganic nitrogen distribution in the Loess Plateau of China.

The semi-arid region of the Loess Plateau is typical of rain-fed agricultural production in Northwestern China. In this area, the ridge mulched system (RM) is a widely-used measure to increase crop yield. The purpose of this study was to investigate the effect of RM on soil water and inorganic nitrogen (N) distribution, and grain yield of maize (Zea mays L.). The study was conducted over three consecutive years and consisted of four treatments (each replicated three times): i) RM with N application rate of 260 kg N ha-1 (RM-N260); ii) RM with 180 kg N ha-1 (RM-N180); iii) a traditional flat cultivation system without mulching (F) with 260 kg N ha-1 (F-N260); iv) F with 180 kg N ha-1 (F-N180). Mean soil water content during the maize growing season was increased by RM in 2013 only. However, RM increased the soil water storage significantly at the 3-leaf (V3) and 6-leaf stage (V6), and decreased evapotranspiration (ET) during pre-silking stage in all years. Compared to F, RM significantly improved maize grain yield by 79-123% in 2013, 23-25% in 2014, and 11-12% in 2015. Following three years of maize cultivation, soil inorganic N content increased substantially (two- to three-fold) in the RM system and 60% of the total inorganic N was accumulated in the top soil layers (0-60 cm) under the mulched ridge. Relative changes were much smaller in F, and most of inorganic N was stored in 0-20 cm and 100-160 cm soil layers. Generally, RM resulted in higher soil water storage during the pre-silking stage, which was the main reason for the improved maize grain yield. The nitrate leaching risk was reduced in RM-N180 compared with F, but nitrate leaching from the furrows between ridges was observed in RM-N260. However, the large increase in soil inorganic N content in RM-N180 after three years' cultivation indicates an oversupply of N and a potential risk of N losses to the environment over the longer term. Our study indicates, therefore, that RM is a suitable system for maize cropping in the semi-arid region of the Loess Plateau, with benefits in water and N use efficiency, but recommendations for appropriate N application rates are required to ensure long term agricultural sustainability, accounting for grain yields and environmental impacts. The mechanisms for inorganic N accumulation under the RM system are not fully understood and warrant further investigation.

[Effect of Film Mulching Age and Organic Fertilizer Application on the Distribution Characteristics of Microplastics in the Soil of a Peanut Field].

The large input of mulch film and organic fertilizer have led to increasingly serious microplastic pollution in farmland soil of China. In this study, the microplastic pollution of peanut farmland in Dezhou City, Shandong Province was investigated. The effects of different mulching years (0, 3, 5, and 8 years) and organic fertilizer application on the abundance, particle size, color, and shape of microplastics in farmland soil were analyzed. The results showed that the average abundances of microplastics in peanut soil were 65.33, 316.00, 1 098.67, and 1 346.34 n·kg-1, respectively, after 0, 3, 5, and 8 years of film mulching. The abundance of microplastics decreased with the increase in soil depth. The abundance of microplastics in 0-10, 10-20, and 20-30 cm topsoil was 1 076.00, 603.5, and 440.25 n·kg-1, respectively, and the abundance of microplastics increased significantly with increasing years of film mulching and organic fertilizer application (P<0.05). The particle size of microplastics in the sample plot <1 mm accounted for 77.30% of the total content, and with the increase in film mulching age, the proportion of microplastics with small particle size (<1 mm) increased significantly (P < 0.05). With the increase in soil depth, the proportion of microplastics with small particle size also gradually increased, whereas the application of organic fertilizer had no significant effect on the particle size of microplastics. The color of microplastics in the plot was mainly transparent (49.77%), followed by black (16.35%) and white (16.27%). The planting age and organic fertilizer application had no significant effect on the color of microplastics in the soil (P > 0.05), but the mulching age significantly increased the proportion of transparent microplastics. The abundance proportion of the five types of microplastics were 49.77%, 25.41%, 19.15%, 3.26%, and 2.41%, respectively. These field soil microplastics were mainly composed of polyethylene (PE), polypropylene (PP), and polystyrene (PS) polymers, accounting for 21.37%, 18.57%, and 19.77% of the total, respectively. Therefore, microplastics were widely present in the soil of the peanut field cultivated layer in Dezhou, Shandong, and the applications of mulch film and organic fertilizer were the main source. This study provides an important basis for the prevention and control of soil microplastic pollution in peanut fields.

Effects of gravel-sand and plastic film mulching on soil water and temperature retention in cold and arid regions without irrigation.

Gravel-sand mulch (GSM) and plastic film mulch (PFM) are important ways of farming in cold and arid regions without irrigation. Nevertheless, there has been a lack of studies of the system response to live weather conditions. To quantify the effects of GSM and PFM on soil moisture and temperature retention, in-situ monitoring experiments were carried out in the arid belt of central Ningxia, China, using continuous monitoring of the field soil water and meteorological conditions at a 30-mimute time-step under three treatments: a bare soil (CK), soil covered by a layer of GSM, and soil covered by GSM and a layer of plastic film (i.e., GSM + PFM). Results show that: (1) With a limited precipitation of 221 mm during the growing season, the average volumetric soil water content (SWC) in the top 30-cm soil layer was lowest for CK, medium high for GSM, and highest for GSM + PFM. Compared to CK, the soil water storage increased by 54 % under GSM and 75.2 % under GSM + PFM; (2) The most frequently occurring low-intensity rainfalls are more efficiently stored in soil under GSM + PFM; (3) Similarly, the soil temperature was significantly increased under GSM and GSM + PFM conditions. Compared to CK, the average soil temperature in the top 5-cm layer increased by 2.5 °C under GSM and 4.8 °C under GSM + PFM during the germination period, which had effectively extended the growing season for about 30 and 50 days, respectively; (4) Although dewfall is only 4 % of rainfall, the total number of dew day was more than twice that of rain day. Thus, dewfall is a more frequent and dependable source of water for native plants and animals. Our results demonstrate that the benefits of GSM and PFM can be applied globally where either insufficient rainfall or low temperatures are limiting factors.

Microplastics in plateau agricultural areas: Spatial changes reveal their source and distribution characteristics.

The Huangshui catchment on the northeastern Qinghai-Tibet Plateau (QTP) was selected as the study area to investigate the abundance, distribution characteristics, and influencing factors of microplastics (MPs) in surface agricultural soils (0-20 cm). The MP levels ranged from 6 to 444 items/kg, with an average of 86 items/kg. The relative abundance of small-sized MPs (<2 mm) was higher than that of large-sized MPs (2-5 mm). Polyethylene was the most common, and residual mulching film in farmland was the main source of MPs. The spatial distribution characteristics of MPs were analyzed through inverse distance weight interpolation, and MP abundance in agricultural soils in neighboring urban areas was significantly higher than that in other areas. Further analysis found that population density was significantly positively correlated with MP abundance (R2 = 0.9090, p < 0.01), indicating that human activities play a key role in MP pollution even in remote areas. In addition, the effects of irrigation, land use type, and soil physicochemical properties on the abundance of MPs were analyzed. Atmospheric transport and irrigation with surface water contribute to soil MP pollution. The direct effects of soil properties on MP abundance are still largely unclear, requiring further studies.

Polyethylene and poly (butyleneadipate-co-terephthalate)-based biodegradable microplastics modulate the bioavailability and speciation of Cd and As in soil: Insights into transformation mechanisms.

Microplastics (MPs) that enter the soil can alter the physicochemical and biochemical properties of soil and affect speciation of heavy metals (HMs), thereby perturbing the bioavailability of HMs. However, the mechanisms underlying these effects are not understood. Therefore, we investigated the effects of MPs from poly (butyleneadipate-co-terephthalate)-based biodegradable mulch (BM) and polyethylene mulch (PM) in Cd- or As-contaminated soil on soil properties and speciation of HMs. MPs were characterised using Fourier-transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). The addition of MPs reduced the bioavailability of HMs in soil and promoted the transformation of HMs into inert fractions. The mechanisms underlying the reduction of the bioavailability of HMs in soils could be as follows: (1) the entry of MPs into the soil changed its properties, which reduced the bioavailability of HMs; (2) FTIR and XPS analyses revealed that the hydroxyl and carboxyl groups and benzene ring present on the surface of aged MPs stabilized complexes (As(V)-O) with As(V) may have directly reduced the bioavailability of As(V) in soil; (3) aged BM exposed more amounts and types of reactive functional groups and was more effective in stabilising soil HMs than PM. Overall, this study provides new insights regarding the complexation mechanisms of soil HMs by MPs from different plastic mulch sources.

Reducing plant pathogens could increase crop yields after plastic film mulching.

Soil fungi are closely associated with crop growth in agricultural ecosystems through processes such as nutrient uptake and pathogenesis. Plastic film mulching (PM) plays a dominant role in increasing crop yields in dryland agriculture worldwide. The functional guilds of soil fungi under PM and their effects on crops remain unclear. In this study, we explored the absolute abundance, diversity, community composition, and functional guilds of soil fungi after short-term (2 years) and long-term (10 years) mulching experiments. Short-term mulching caused a 37 %-51 % decrease in absolute fungal abundance owing to abrupt changes in the microenvironment. The response of the fungal community to PM varied with sites, with the effect being more pronounced under poor hydrothermal conditions (314 mm). The abundance of potential fungal pathogens decreased under PM; for example, Gibberella (maize ear rot) abundance was 45 % and 72 % lower under short- and long-term mulching, respectively, when compared with that in control. In contrast, the abundance of plant biocontrol fungi increased under PM; for instance, Glomeromycota abundance increased twofold under long-term mulching. Although PM did not alter the complexity and stability of fungal co-occurrence network, competition among fungi increased in the absence of sufficient carbon (C) sources. Long-term mulching reduced phytopathogen guilds by 12 %-77 % and increased arbuscular mycorrhizal fungi (AMF) guilds by 89 %-94 %. Structural equation modeling suggested that PM altered fungal functional guilds mainly by shaping the structure of the fungal community, and fungal pathogens decreased with increased AMF functional guilds, inducing higher maize yields. These results showed for the first time, from a microbial perspective, that pathogens reduction owing to PM could explain 4.4 % of maize yield variation, providing theoretical guidance to accomplish sustainability of continuous maize mulching.

The prolonged effect of film mulch and P application on lucerne forage yield in a semiarid environment.

Introduction: Limited water and soil phosphorus (P) availability often hampers lucerne productivity in semiarid regions. Plastic film mulch and P application typically enhance young lucerne (2-3 years) productivity by increasing soil water use and P availability. However, the prolonged impact of film mulch and P application on lucerne productivity as the stand ages remains unclear. Methods: This study conducted a 9-year field experiment on the semiarid Loess Plateau to investigate how film mulch and P application affect lucerne forage yield, soil water content, and soil fertility. The field experiment used a split-plot design with randomized blocks, in which the whole plots were with (M1) and without plastic film mulch (M0), and the split plots were four P rates (0 (P0), 9.7 (P1), 19.2 (P2), and 28.8 (P3) kg P ha-1). Results and discussion: The M1 treatment produced significantly higher lucerne forage yields than the M0 treatment during the first five years, but the yield-increasing effect of film mulch gradually diminished over time, with no effect in Years 6-8, and lower yields than the M0 treatment in Year 9. Phosphorus fertilization significantly increased forage yield after Year 3 in the M0 treatment, but only in Years 3-5 in the M1 treatment. In Years 2-5, film mulch significantly increased soil organic carbon, total nitrogen (N), inorganic N, and microbial biomass carbon in P0, P1, and P2 but not in P3. However, in Years 7-9, film mulch significantly decreased soil available potassium (K), organic carbon mineralization, lucerne density, and shoot K concentration, but did not reduce soil N and P availability at any level P of application. Moreover, plastic film mulch significantly increased the soil water content at 0-300 cm deep from Year 7 onwards. In conclusion, film mulch ceased to enhance lucerne production beyond year 6, which could not be attributed to soil water content, N or P availability but was partially associated with reduced soil K availability. Consequently, future research should focus on soil K availability, and K addition should be considered after five years in lucerne pastures mulched with plastic film in semiarid areas.

Effects of biodegradable and polyethylene film mulches and their residues on soil bacterial communities.

To investigate the effects of plastic film mulches and their residual films after use on soil bacterial communities, mulching experiment and the subsequent residual film experiment were conducted on winter-planting potato field in two locations. During mulching experiment, treatments biodegradable film mulch (BM) and PE film mulch (PM) reduced soil nutrient regarding available nitrogen and available potassium, as well as microbial biomass carbon (MBC), but increased urease activity, as compared to treatment no film mulch (NM). Soil moisture was significantly elevated by mulching practices and correlated with more microbial phyla than the other tested soil properties, indicating its important role in shaping soil bacterial communities. In addition, mulching practices increased alpha diversity of soil bacteria, although location heterogeneity was observed. Network analyses showed that both treatments BM and PM promoted the interrelations within bacterial communities and harbored more keystone taxa than treatment NM. During residual film experiment, residual films from BM and PM were incorporated into soil after harvest of potato. Treatment residual biodegradable film (RBF) significantly increased the content of MBC and activity of ß-glucosidase (BG) as compared to treatments residual PE film (RPF) and no residual film (NRF), and BG had the most correlations with microbial phyla among all the tested soil properties. Treatments RBF and RPF increased the relative abundance of some dominant bacterial phyla, including Bacteroidetes, Actinobacteria, and Chlorofexi, and enhanced the interrelations within bacterial community, whereas more keystone taxa were harbored by treatment RBF, due to the increase of keystone taxa in phyla Acidobacteria, Actinobacteria, Bacteroidetes, and Proteobacteria. These results indicate that the indirect effects of biodegradable and PE film mulch as a soil surface barrier on soil are similar, whereas their direct effects via incorporation into soil as residual films show specificity.

Black Plastic Film Mulching Increases Soil Nitrous Oxide Emissions in Arid Potato Fields.

Black plastic film mulching is a common practice for potato production in the arid area of Northwest China. Many studies have reported the significant positive effect of black plastic film mulch on potato harvest, while the effect of black plastic film mulch treatment on soil nitrous oxide (N2O) emissions is still unclear. As a consequence, this study aimed to examine the effect of black plastic film mulch treatment on N2O emission from arid upland potato fields. With the static chamber-gas chromatography method, soil N2O emissions were measured. The results showed that black plastic film mulching treatment significantly increased cumulative soil N2O emissions by 21-26% compared with non-mulched treatment. Cumulative N2O emission positively correlated with soil temperature, soil moisture, soil CO2 concentration, and amoA-AOB abundance. This study indicated that black plastic film mulching, mainly through increasing soil temperature and soil moisture, increasing soil carbon dioxide (CO2) concentration, and promoting the abundance of nitrification-related functional gene of amoA-AOB, regulated N2O emissions. This study also highlighted that the specific soil environment under black plastic film mulch is conducive to N2O emissions and lay the foundation for settling the contradiction between food production and greenhouse gas mitigation in upland soils. The negative effects of black plastic film mulching on the environment should be considered in future applications in food production.

Maize Lodging Resistance with Plastic Film Removal, Increased Planting Density, and Cultivars with Different Maturity Periods.

While plastic film mulching and proper high-density planting are important methods that can improve maize yield, years of accumulated residual film have created soil pollution and degraded soil, and thus has impeded sustainable agriculture development. Here, we compared the stalk and root lodging resistances of three maize cultivars grown at two planting densities both with (FM) and without (NM) plastic film mulch. Our aim was to provide a theoretical basis that may help assure a future of successful no-film planting with increased planting density. The results showed that, compared with FM, the average dry weight per unit length and bending strength of basal internode decreased for all cultivars at both planting densities in the NM treatment. At 9.0 × 104 plants ha-1, the stalk breaking force (SFC) of Xinyu77, KWS9384, and KWS2030 in the NM treatment decreased by 4%, 21%, and 22%, respectively. At 12.0 × 104 plants ha-1, SFC of Xinyu77 and KWS2030 increased by 14% and 1%, respectively, while KWS9384 decreased by 10%. Additionally, the root diameter, length, volume, width, depth, and the vertical root-pulling force of maize decreased. Although the lodging resistance of maize grown without film mulch was lower than that of maize grown with it, those adverse effects can be mitigated by selecting suitable cultivars and by using proper high-density planting and appropriate cultivation measures.

Plastic-Film Mulching for Enhanced Water-Use Efficiency and Economic Returns from Maize Fields in Semiarid China.

Film mulch has gradually been popularized to increase water availability to crops for improving and stabilizing agricultural production in the semiarid areas of Northwest China. To find more sustainable and economic film mulch methods for alleviating drought stress in semiarid region, it is necessary to test optimum planting methods in same cultivation conditions. A field experiment was conducted during 2013 and 2014 to evaluate the effects of different plastic film mulch methods on soil water, soil temperature, water use efficiency (WUE), yield and revenue. The treatments included: (i) the control, conventional flat planting without plastic film mulch (CK); (ii) flat planting with maize rows (60 cm spacing) on plastic film mulch (70 cm wide); (iii) furrow planting of maize (60 cm spacing), separated by consecutive plastic film-mulched ridges (each 50 cm wide and 15 cm tall); (iv) furrow planting of maize (60 cm spacing), separated by alternating large and small plastic film-mulched ridges (large ridges: 70 cm wide and 15 cm tall, small ridges 50 cm wide and 10 cm tall); and (v) furrow-flat planting of maize (60 cm spacing) with a large plastic film-mulched ridge (60 cm wide and 15 cm tall) alternating with a flat without plastic film-mulched space (60 cm wide). Topsoil temperature (5-25 cm) was significantly (p < 0.05) higher in field plots with plastic film mulch than the control (CK), and resulted in greater soil water storage (0-200 cm) up to 40 days after planting. Maize grain yield and WUE were significantly (p < 0.05) higher with the furrow planting methods (consecutive film-mulched ridges and alternating film-mulched ridges) than the check in both years. Maize yield was, on average, 29% (p < 0.05) greater and 28% (p < 0.05) greater with these furrow planting methods, while the average WUE increased by 22.8% (p < 0.05) with consecutive film-mulched ridges and 21.1% (p < 0.05) with alternating film-mulched ridges. The 2-year average net income increased by 1559, 528, and 350 Chinese Yuan (CNY) ha-1 with the consecutive film-mulched ridges, furrow-flat planting and alternating film-mulched ridges, respectively, compared with the control (CK). We conclude that the consecutive film-mulched ridge method was the most productive and profitable for maize in this semi-arid area with limited and erratic precipitation.