Effects of biodegradable and plastic mulches on soil biogeochemical cycles in an agricultural system

Agricultural soils perform important ecological functions and agricultural practices affect the maintenance of these functions. Mulching is an agronomic technique, consisting of covering the soil with a protective layer of natural or artificial materials. Mulching influences soil temperature and moisture, promotes the development of microorganisms, allows the release of nutrients and reduces the development of weed species, improving crop growth. The aim of the research was to evaluate the effect of Low-density polyethylene based mulching film (LDPE) and biodegradable Mater-bi® (thermoplastic starch) based mulching films on soil organic matter and microbial enzyme activities linked to biogeochemical cycles of C, N and P.

The experimental field was established at an organic farm (Capua, Caserta, Southern Italy), under a greenhouse environment. According to organic farming management, soil was amended with green manure and on farm compost. The experiment was carried out in a randomized block design with five treatments replicated four times: soil covered with LDPE film, soil covered with Mater-Bi® films of 3 different thicknesses (18, 21, 25 μm), bare soil in area not mulched under the same tunnel as control. The films were placed on soil surface in October 2021, then strawberry was planted and cultivated until June 2022. After 7 months, in correspondence with the maximum strawberry production, soil was sampled (at 20 cm depth), sieved (2 mm) and samples analysed for organic matter content (by calcination in muffle) and enzyme activities (hydrolase, β-glucosidase, phosphatase and β-glucosaminidase by spectrophotometric method).

The soil organic matter content showed higher value in control soil (4.22%) respect to soil covered with LDPE and Mater-Bi® films 25 µm (on average 3.56%). The β-glucosidase activity showed the highest value in the soils covered with Mater-bi® 18 µm, whereas the hydrolase, phosphatase and β-glucosaminidase showed no significant differences among treatments. Therefore, the application of biodegradable plastic films did not show clear effect on soil organic carbon stock after 7 months, likely due to the high organic matter content characterizing this soil. However, as the enzyme β-glucosidase is involved in the C-cycle, the results indicated a possible effect on this activity due to a faster degradation of the thinnest biodegradable plastic film (Mater-bi® 18 µm). Enzyme activities are sensitive indicators and provide rapid responses compared to soil chemistry analyses, in particular β-glucosidase is significantly correlated with agronomic practices, and it is able to quickly detect changes in soil management. The study of enzyme activities as indicators of soil quality can provide useful data to implement agricultural sustainable management strategies.