Soil refinement accelerates in-field degradation rates of soil-biodegradable mulch films

Abstract

Soil-biodegradable mulch films are a promising solution to replace conventional polyethylene-based mulch films, the use of which has led to negative environmental impacts. Soil-biodegradable mulch films are specifically designed to be incorporated into the soil at the end of the cropping cycle, and are expected to be biodegraded by soil microorganisms. The biodegradability of such products must be tested under laboratory-controlled conditions following international standards, although these can fail to represent real environmental conditions where mulch films are used. The objective of this study was to evaluate the effects of soil refinement on the degradation rates of three different commercial soil-biodegradable mulch films after their incorporation into the soil. The hypotheses were that: (i) soil refinement (i.e., ploughing followed by grubbing) creates more favourable conditions for film biodegradation compared to ploughing alone; and (ii) different mulch films show different degradation rates. An open-field completely randomised design was applied to test the effects of soil refinement by ploughing to 0.35 m depth without and with subsequent grubbing to 0.15 m depth twice. Three commercially available soil-biodegradable mulch films were sampled in 2020 (i.e., two Mater-bi-based, one Ecovio-based) at the end of a zucchini growing season (~3 months) when films were still lying above ground, and were later buried at 0.2 m depth inside mesh bags. Biodegradation rates of the sampled films were assessed with the indirect indicators of film weight loss and surface area loss at ~2-month intervals over 314 days. The results showed that soil refinement significantly accelerated degradation of the three tested mulch films by 14% and 17% according to the loss of weight and surface area indicators, respectively. One Mater-bi-based film showed higher degradation rates compared to the other two films. Future studies are needed to quantify the time needed for these different mulch films to be completely biodegraded. Such studies should be carried out following standards for laboratory incubation and/or in-field quantification of residual polymers in the soil over time. Highlights- Degradation rates of three biodegradable mulch films were evaluated in the open-field.- Soil refinement accelerates the degradation of film weight (14%) and surface (17%).- Highest degradation rates were observed for one Mater-bi-based film.- Fastest degradation rates were observed in spring for all the tested films.- Weight and surface area loss indicators showed positive relationship.

Effects of crop residue incorporation on soil‐biodegradable mulch film degradation in a broccoli‐sorghum rotation system

“…In any case, area loss may be a better indirect indicator of biodegradation than mass loss, as the latter showed questionable results, in some cases appearing to increase over time (Figure 2F). Indeed, other studies have reported that area loss is a more reliable indicator than mass loss (e.g., Bianchini et al, 2022).…”

“…Examples include studies that have investigated the degradation of soil-biodegradable mulch films into macro and then microplastics followed by a quantification via chemical extraction (Li et al, 2023). Some other studies have placed mulch film samples in mesh bags, which allow the adhesion of soil to the film, ensuring the passage of water and microorganisms (Bianchini et al, 2022;Sintim et al, 2020;Tsuboi et al, 2022). In these studies, film area or mass loss, measured with infrared spectroscopy or nuclear magnetic resonance, was used to estimate degradation.…”

“…After weighing, samples were scanned with an image scanner (Docu Centre-V 5080 N; Fuji Xerox). Each image was then processed using the ImageJ software (National Institutes of Health and the Laboratory for Optical and Computational Instrumentation, University of Wisconsin) following the method described by Bianchini et al (2022). The area loss of each film sample was automatically calculated by the ImageJ software and was expressed as a proportion (%) of the remaining area.…”

“…Among the few available open-field studies, some have assessed the degradation rates of mulch films under various pedo-climatic conditions (e.g., Sintim et al, 2020), while others compared degradation rates in laboratory vs. field conditions also addressing the issue of potential plastic accumulation over the years (Griffin-LaHue et al, 2022). In a recent study, it was highlighted that the combination of plowing and grubbing can accelerate the degradation rate of mulch film at the end of a zucchini cropping cycle (Bianchini et al, 2022). Other openfield studies have evaluated the degradation behavior of film of mulch films either before (Liu et al, 2022) or after their incorporation (Li et al, 2023), or have focused solely on their impact on crop yields and quality (Wang et al, 2021).…”

Use of biodegradable plastic films in agriculture and their fate in soil

“…In particular, pNP-C4 hydrolytic activity can aid in the detection of the microbial activity associated with the biodegradation of polyester-based biodegradable mulch films in cultivated field soils. Bianchini et al (2022) conducted open-field experiments where they evaluated the effects of soil refinement on the degradation rates of three different commercial soil-biodegradable mulch films after their incorporation into the soil. Their results show that soil refinement significantly accelerated the degradation of the tested films.…”