Chili is a vital cash crop in many countries, and Sri Lanka is no exception. As one of the pillar industries of the country’s agriculture, chili not only meets domestic consumption needs but also is exported to markets such as India, the Middle East, and Europe in the form of processed products like dried chili and chili powder, supporting the livelihoods of numerous smallholder farmers. However, local farmers have long faced challenges including water scarcity, nutrient loss, and weed competition. Particularly against the backdrop of climate change exacerbating erratic rainfall, yield stability is severely threatened.
To address these issues, plastic film mulching (PFM) has been widely adopted. It promotes crop growth by reducing soil evaporation, regulating temperature, and improving water use efficiency. Nevertheless, the long-term use of traditional non-biodegradable mulches (such as polyethylene mulch) leads to soil microplastic accumulation and ecological pollution. The effectiveness and sustainability of biodegradable mulches in high-rainfall wet zone agriculture have not been fully verified.
So, in ecologically sensitive regions like Sri Lanka’s wet zone, how do different types of plastic mulches affect soil properties and chili yield? Can biodegradable mulch emerge as a viable alternative that balances productivity and environmental protection?
Dr. Mojith ARIYARATNA from the Department of Crop Science, Faculty of Agriculture, University of Peradeniya, Sri Lanka, and his colleagues conducted a field experiment in the country to systematically compare the effects of three types of plastic mulches: black non-biodegradable low-density polyethylene (LDPE) mulch, silver-black reflective LDPE mulch, and polylactic acid-polybutylene adipate-co-terephthalate (PLA-PBAT) biodegradable mulch, with unmulched soil as the control. The experiment lasted for 7 months, covering both dry and wet seasons, and the chili variety cultivated was “MICH HY-1”, which is widely grown locally. Researchers regularly measured soil physicochemical properties and crop growth indicators to evaluate the comprehensive impact of different mulches on chili production. The relevant article was published in Frontiers of Agricultural Science and Engineering (DOI: 10.15302/J-FASE-2025648).
The results showed that all mulch treatments significantly improved soil conditions and crop performance. In terms of soil moisture retention, the gravimetric moisture content (GMC) of mulched groups was higher than that of the control group at multiple key time points. The biodegradable mulch performed particularly well during the dry period; for example, the soil moisture content reached 23.6% at 8 weeks after planting, significantly higher than the control group’s 9.3%. Regarding soil temperature, the black non-biodegradable mulch had the most pronounced warming effect, with the highest temperature reaching 33.3 ℃, while the control group consistently maintained the lowest temperature. This helps promote chili root activity and nutrient uptake.
Nutrient retention is another important function of mulches. The experiment found that mulching effectively reduced the loss of soil nitrate nitrogen (NO₃^–) and available phosphorus (P), but had no significant effect on ammonium nitrogen (NH₄⁺). In addition, although mulching did not change soil pH, it increased electrical conductivity (EC), indicating an accumulation of soluble salts and nutrients in the soil, which is associated with reduced leaching loss.
In terms of crop growth and yield, the advantages of mulch treatments were more significant. Chili plants under non-biodegradable mulch had the highest plant height; the biodegradable mulch achieved the highest total yield, followed by the reflective mulch and non-biodegradable mulch. Notably, the biodegradable mulch showed stable performance in all harvests, and its final biomass was comparable to that of non-biodegradable mulch, demonstrating its substitution potential in terms of productivity.
This study systematically evaluated the comprehensive performance of biodegradable mulch and traditional mulch in Sri Lanka’s wet zone. Previous studies have mostly focused on arid or semi-arid regions, while data on the effectiveness and environmental risks of mulches under high rainfall conditions in wet zones has been lacking. This research indicates that biodegradable mulch is comparable to non-biodegradable mulch in maintaining soil moisture, nutrients, and crop yield, while avoiding plastic residue problems, providing a feasible solution for sustainable agriculture in tropical high-rainfall regions.
DOI: 10.15302/J-FASE-2025648