Mulch film field degradation experiment
Mulch film degradation field experiment
Worldwide, the use of agricultural plastic mulch films has been encouraged over the past 50 years, to promote food security and increase livelihoods of farmers. However, the rapidly accumulating plastic legacy in the soil is now posing a new problem to tackle. Since removing plastic mulches from fields can be extremely difficult and proper disposal facilities are rare, a lot of farmers have adopted a strategy of ploughing the mulch film into the soil after harvest. The long-term effects of this plastic legacy in soil are still poorly understood, however there has been a change in the industry in the last few years and many farmers are now switching from conventional plastic mulch films to biodegradable alternatives.
This 12-month field experiment (2021-2022) is investigating the degradation rates of 8 different types of mulch film, 2 of them commercially available and commonly used in the UK, and 6 of them with new formulations made in-house at the BioComposites Centre. The experiment focuses on the degradation of these films above ground (caused by UV irradiation), and below ground (caused by soil microbial processes).
To monitor the UV degradation, films were laid out onto ploughed soil to simulate normal agricultural practices, with 4 replicates per film type. Films were sampled monthly and changes in spectra were analysed using FTIR-ATR spectroscopy.
The key measurements for this part of the experiment include soil surface temperature, UV irradiation, temperature, microplastic production of degrading films, soil moisture content, and visual and chemical degradation of films.
To determine the degradation of the films in soil, 4 replicates of each film (plus control = no film) were buried in nylon mesh bags filled with soil. The mesh bags had two different sizes to allow for interaction with macro-, meso-, and microfauna (5000µm), and interaction with only microfauna (100µm). The mesh bags were excavated after 4, 8, and 12 months.
The key measurements for this part of the experiment include soil moisture & temperature, soil physical properties (pH/EC/ammonium/nitrate), carbon & nitrogen content, microplastic contamination of the soil, and microbial diversity (16S & 18S/ITS).
Overhead view of mulch film degradation trial plastics field layout.
Fine mesh (100 μm) bag containing soil and plastic mulch film. Mesh size permits entry of soil microfauna only.
Wide mesh (5000 μm) bag allowing entry of large soil fauna.