Biodegradable plastic mulch residues impair wheat growth more than polyethylene

Why It Matters

This research highlights the unintended consequences of using plastic mulching in agriculture, even with materials marketed as biodegradable. Designers and engineers developing agricultural materials need to consider the full life cycle impact and potential soil contamination.

Key Finding

Plastic residues in soil, especially biodegradable types, hinder wheat development. Earthworms can help reduce these negative impacts.

Key Findings

• Macro- and micro- plastic residues negatively affected wheat growth, impacting both above-ground and below-ground parts.
• Biodegradable plastic mulch residues exhibited stronger negative effects on wheat growth compared to polyethylene residues.
• The presence of earthworms generally had a positive effect on wheat growth and helped to alleviate the negative impacts of plastic residues.

Research Evidence

Aim: To investigate the effects of macro- and micro- plastic residues from low-density polyethylene and starch-based biodegradable plastic mulch films on wheat growth in soil, with and without the presence of earthworms.

Method: Controlled Pot Experiment

Procedure: Wheat was grown in sandy soil mixed with 1% concentration of either low-density polyethylene or starch-based biodegradable plastic mulch residues. The experiment was conducted in a climate chamber, with some pots including earthworms to assess their mitigating role. Both above-ground and below-ground plant growth parameters were measured during vegetative and reproductive stages.

Context: Agricultural soil and crop production

Design Principle

Prioritize soil health and ecosystem integration in material selection for agricultural applications.

How to Apply

When developing or selecting materials for agricultural use, conduct thorough life cycle assessments that include potential soil contamination and impact on soil ecosystems. Consider designing for complete and safe degradation or for easy removal and recycling.

Limitations

The study used a controlled laboratory setting (climate chamber) and a specific soil type (sandy soil) at a fixed concentration of plastic residue (1%). Field conditions and varying soil types or plastic concentrations may yield different results.

Student Guide (IB Design Technology)

Simple Explanation: Putting bits of plastic, even 'biodegradable' ones, into soil can harm how wheat grows. Earthworms can help make the plants healthier.

Why This Matters: This research is important for design projects involving agriculture because it shows that even materials designed to be better for the environment can have negative consequences if not fully understood.

Critical Thinking: Given that biodegradable plastics can still negatively impact soil health, what are the criteria for truly sustainable agricultural materials, and how can designers ensure these criteria are met?

IA-Ready Paragraph: Research indicates that plastic residues in agricultural soils, including those from biodegradable mulch films, can negatively impact crop growth. For instance, a study by Qi et al. (2018) found that both polyethylene and biodegradable plastic mulch residues impaired wheat development, with biodegradable plastics showing a more pronounced negative effect. This highlights the critical need for designers to consider the long-term ecological consequences of material choices in agricultural applications.

Project Tips

• When researching materials for agriculture, look beyond just the intended function and consider the material's end-of-life impact on the environment.
• Investigate how natural processes or organisms might interact with and affect the performance and impact of your chosen materials.

How to Use in IA

• Use this research to justify the selection of alternative materials or to highlight the potential environmental risks of certain material choices in your design project.

Examiner Tips

• Demonstrate an understanding of the full life cycle of materials, including their impact on ecosystems beyond their primary function.

Independent Variable: ["Type of plastic residue (polyethylene, biodegradable plastic, none)","Presence of earthworms (yes, no)"]

Dependent Variable: ["Wheat growth (above-ground biomass, below-ground biomass, plant height, etc.)"]

Controlled Variables: ["Soil type (sandy soil)","Plastic concentration (1%)","Climate conditions (climate chamber)","Wheat variety (Triticum aestivum)"]

Strengths

• Investigated both macro- and micro- plastic forms.
• Included the role of a key soil organism (earthworms) in mitigating plastic effects.

Critical Questions

• What are the long-term effects of these plastic residues on soil microbial communities and nutrient cycling?
• How do different types of biodegradable plastics vary in their impact on soil and plant health?

Extended Essay Application

• Investigate the degradation rates and by-products of various biodegradable agricultural films under different environmental conditions.
• Design and test alternative, non-plastic mulching solutions for crop production.

Source

Macro- and micro- plastics in soil-plant system: Effects of plastic mulch film residues on wheat (Triticum aestivum) growth · The Science of The Total Environment · 2018 · 10.1016/j.scitotenv.2018.07.229