Effects of increased plastic film residues on soil properties and crop productivity in agro-ecosystem

https://doi.org/10.1016/j.jhazmat.2021.125521Get rights and content

Highlights

  • LDPE and Bio film residue significantly lowered maize productivity and water use.

  • Soil bulk density was thus increased while soil porosity decreased significantly.

  • Increased residues improved soil N content but lowered C/N ratio significantly.

  • Increased residues reduced microbial biomass C and N levels with no change in C/N.

  • Bio residues affected soil properties and productivity similarly as LDPE ones did.

Abstract

Intensive use of low-density polyethylene (LDPE) plastic films in agro-ecosystems has raised considerable concerns due to the increasing film residues in soils. It is unclear how the increased film residues affect soil properties and crop productivity and whether biodegradable (Bio) film can substitute LDPE. To address the issue, we designed a landfill experiment with different addition levels of plastic residue into soils of maize (Zea mays L.) field from 2018 to 2019. Six treatments were arranged as PMT1-T3/BioT1-T3, representing the low, medium, and high-level application of LDPE / Bio film fragments, with no residual film, applied as CK. Results show that, soil bulk density was significantly increased from 1.19 to 1.31 g/cm3 regardless of residue types. In contrast, soil porosity was lowered from 58.03% in CK to 57.36% in Bio and 56.12% in LDPE significantly (P < 0.05). Increased residues improved soil nitrogen level and lowered the C/N ratio significantly. Also, it decreased microbial biomass C and N levels but with no change in C/N (P < 0.05). Maize yield and WUE decreased, while soil water storage increased significantly. LDPE residues affected soil properties and productivity partly lower than Bio ones did, but the negative effects of them were similar in the maize field.

Introduction

Since mulching film technology was introduced to China in 1978, it has become one of China's most important agronomic technologies. According to statistics, the current use of mulch in China has reached up to 1.362 million tons and crop mulch coverage area up to 167.57 million/ha (Rillig et al., 2017). In terms of plastic mulch quantity and coverage, China is the largest consumer of these synthetic films globally, and mulching film has become an indispensable material for sustained crop production (Rillig et al., 2019). Currently, plastic mulch films accounted for over 40% of the total plastic films used in agriculture (Jiang et al., 2017). The extensive use of plastic film mulches has been necessitated by the fact that 40% of total arable lands in China are located in the arid and semi-arid Loess Plateau, a region where water is a limiting factor, receiving annual rainfall amount from 150 to 300 mm in the northern part, and from 500 to 700 mm in the south (Liu et al., 2014). Low-density polyethylene (LDPE) plastic film used as mulch in the ridge-furrow system has been extensively adopted in China, especially the Loess Plateau. It has played an important role in crop production systems (Ghimire et al., 2020). It has led to increased crop yields and quality due to the cumulative benefits in the control of weeds, the moderation of soil temperature, the conservation of soil moisture, and the minimal loss of nutrients (Jiang et al., 2017).

The widespread use of LDPE plastic film has resulted in large amounts of film residues in soils, which has raised concerns about possible pollution risks (Gao et al., 2019). The mulching film's residual amount has reached up to 72–259 kg/ha (Scalenghe, 2018). This huge accumulation of plastic residues was rapidly increasing due to the long-term, extensive use of plastic film. Also, the thinness of plastic film used for mulching and the low rates of recovery of used plastic films at the end of crop season by the farmers are among the major reasons (Li et al., 2016). Many plastic film residues might destabilize the soil structure and affect the quality of soil, resulting in gradual decreases in soil permeability and soil porosity. This would affect the water and nutrient movement in soils, crop growth, and development (Qi et al., 2019).

Soil permeability and other physical properties can hinder crop roots' vertical growth, eventually resulting in reduced crop yield (Wang et al., 2015). The increased residual films in soils were viewed as a critical factor restricting the capillary water migration path in soils and reducing soil water carrying capacity (Li et al., 2015). It has been reported that film residues decreased soil porosity and air circulation, inevitably changing microbial communities' dynamics and causing low soil fertility, with detrimental effects on crop seed germination and seedling growth (Wang et al., 2016). So far, plastic film residues in the arable soil layer for possible implications on the soil-plant system and agro-ecosystems have not been documented. Due to its potential serious influences on the soil-plant system, the relevant studies on the potential impacts of the residues in soil on various crop production needed to be conducted for future decisions to use and apply plastic films (Qi et al., 2018). On the other hand, biodegradable (Bio) plastic films are widely recognized as a substitute to currently widely used LDPE films since they can gradually be degraded in soils. The reduced residue accumulation is always a core mission (Qi et al., 2019).

It is urgently needed to conduct such investigations on how residual mulching film blocks water, nutrient, and heat transfer in soils and why the soil ecosystem's disruption exerts an adverse effect on crop production. Further studies in this area need to be done to debunk the myth surrounding plastic mulching system pollution worldwide (Wang et al., 2016). The relationship between maize (Zea mays L.) crop yield and the amount of residues in the soil is largely unknown (Dong et al., 2015). The critical amount of plastic residue that can reduce crop yield significantly needs to be established for better mitigation measures to be put in place (Gao et al., 2019). Therefore, this study sought to investigate the effects of these unrecovered plastic film residues, especially on the top 30 cm of soil, on the maize growth and productivity, and soil mass. To obtain an assessment on this topic, a field experiment was conducted for two consecutive years to investigate the increased residues' influence on maize productivity, soil physical and chemical properties. The major objectives of this study are as follows: 1) to evaluate the effects of increased LDPE and Bio film residues on maize growth, water use, and yield formation, 2) to determine the effects of two types of residues on soil physical and chemical properties after two-year addition and 3) to identify whether Bio film can substitute the usage of LDPE one in the perspective of crop productivity and soil properties.

Section snippets

Experimental site description

The field experiment was performed at the Semiarid Ecosystem Research Station of Lanzhou University at Zhonglianchuan village, Yuzhong County (36.03N, 104.25E, and 2400 m above sea level), Gansu, China. The experimental site's long-term annual mean (average for the last 30 years) air temperature is 6.0 °C, monthly maximum temperature 19.5 °C (July), and monthly minimum temperature − 8.5 °C (January). During the study period, the average annual precipitation was 370 mm, which about 65% falls

The responses of soil bulk density (BD) and porosity dynamics to increased residues addition

Our study showed higher bulk densities and lower porosities in all the treatments in the 2019 growing season than the 2018 season. PMT3 and BioT3 treatments had significantly higher bulk densities and subsequently lower porosities than other treatments in the two-year study period. In 2018, CK and BioT1 had the highest porosity of 58.1% and 57.9%, respectively, with PMT3 and BioT3 1.3% lower on average compared to CK and BioT1. CK, BioT1, and PMT1 had the lowest bulk densities and significantly

Discussion

This study provides evidence of the relationship between the amounts of plastic film residues in soil and the soil water storage in different maize growth stages. The presence of plastic film residues altered soil water storage dynamics and eventual crop water consumption, directly affecting biomass accumulation throughout the growing stages and the maize yield. The higher the quantity of plastic residues incorporated in the soil, the higher the amount of SWS within the soil columns with

Conclusion

In this study, the results showed that regardless of the type of plastic film used, the higher the residue film content in the soil, the more significant the impact on soil maize productivity and soil physical properties. The plastic residue influence on soil's physical and chemical properties, including soil bulk density, porosity, soil moisture, and soil nutrients were pronounced in treatments with high amount of residues. The residual effects tended to be aggravated with the increase of film

CRediT authorship contribution statement

Kiprotich Koskei (First author): Conceptualization, Investigation, Formal analysis, Methodology, Software, Writing-original draft, Writing-review & editing, Visualization. Alex Ndolo Munyasya: Conceptualization, Investigation, Formal analysis, Writing - original draft. Wesly Kiprotich Cheruiyot: Writing - review & editing, Visualization. Yi-Bo Wang: Resources, supervision. Rui Zhou: Resources, supervision. Sylvia Ngaira Indoshi: Conceptualization, Data curation, Formal analysis, Investigation.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

The authors greatfully acknowledge the immense financial support by the National Specialized Support for Outstanding Talents, China, under grant number; 2018-29-5, Open Funding Project of State Key Laboratory of Grassland Agro-ecosystems, China (Hosted by J.L. Xiong), Overseas Master’s Program of Ministry of Education, China under grant number; Ms2011LZDX059, National Key Technology Support Program, China under grant number; 2015BAD22B04 and the Core Facility of School of Life Sciences, Lanzhou

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K. Koskei and A.N. Munyasya equally contribute to this work.

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