Soil Sampling and Field Experiments
Large scale sampling surveys in each country will allow us to assess the quantities and types of macro-, micro- and nano-plastics found in soils from typical cropping systems. The surveys will be complemented by data from existing on-farm Long Term field Experiments (LTEs), and new field experiments have been set up in all countries to directly measure the effect of adding plastics to soil on physical, chemical and biological soil quality indicators (WP2).
The focus of WP3 will be investigating the levels of plastics and co-contaminants such as pesticides, heavy metals and dyes that are present in crops in the soil sample survey area, and in those grown in the WP2 experiments. The potential for direct uptake of plastics by plants will be assessed in mesocosm experiments where particles of 14C-labelled plastic will be applied to soil.
In the first common long term experiment, the effects of conventional and biodegradable mulch films on crop and soil health are investigated. The use of plastic mulch film in an agricultural context has been actively encouraged in many regions of the world, improving water and nutrient use efficiency, crop yields and food security. However, plastic mulch film is extremely difficult to remove from the soil, which results in the plastic films being ploughed back into the soil, leading to an accumulation of legacy plastic in agricultural fields. The majority of short- and long-term effects and fate of conventional and biodegradable plastic films in soil are still undetermined.
In this multi-year experiment, the effects of conventional and biodegradable mulch films on soil and crop health are investigated, whilst also looking at the degradation of the plastic films and the potential microplastic contamination of the soil. The experiment is being repeated in all partner countries, following a common protocol with some local variations. There are three main treatments: control (no film), a conventional plastic film (low density polyethylene, LDPE) and a biodegradable film (a blend of polybutylene adipate terephthalate (PBAT)/polylactic acid (PLA)). As well as using the same UK-sourced films, all countries have additional treatments with local films. There are four replicates of each treatment laid out in a random block design. The crop grown varies according to local circumstances. We are investigating the effects on plant growth dynamics, nutrient cycling, greenhouse gas emissions and soil health, including microbial community changes.
The experiment is repeated at least annually, using the same plots as in the previous year. Before each replanting, any remaining film of the previous growing season is incorporated into the soil, simulating a realistic plastic accumulation in agricultural fields.
Key soil measurements for this experiment include:
- soil moisture and temperature
- soil physical properties (pH, EC, ammonium, nitrate)
- carbon and nitrogen content
- nitrogen retention of the soil (15N)
- greenhouse gas emissions
- microbial diversity (16S & 18S/ITS)
Plant measurements include:
- chlorophyll content
- growth dynamics
- carbon and nitrogen content
- nitrogen uptake (15N)
- microplastic and/or additive uptake
Plastic film measurements include:
- signs of visible degradation
- production of microplastics
- chemical changes in the polymers caused by UV exposure and/or soil microbial breakdown.
More information about this experiment in different countries and other planned experiments are available on the individual country pages: