Agronomic performances of biodegradable films as an alternative to polyethylene mulches in vineyards

The use of polyethylene (PE) mulch at planting ensures the successful and homogeneous establishment of vineyards and also leads them to produce one year earlier. However, as they are rarely removed from the vineyards, the aesthetic and environmental impact of those films is devastating. In addition, the long-term stability of conventional plastics appears disproportionate with respect to the material lifespan required in mulching practices. To face up this issue biodegradable films already used in horticulture would be an environmentally friendly alternative provided that they meet the requirements of the perennial crop and associated farming practices i.e., remain intact in the field long enough to provide its expected positive effects on the crop and then, biodegrade on the soil surface without additional ploughing. The performance and environmental impact of commercially available biodegradable mulch films displaying different thicknesses were studied through two consecutive full-scale field experiments conducted in the south of France. The impact of mulching on soil properties and agronomic performance was measured during the three first crop cycles by monitoring vine growth and fruiting yield concomitantly with film ageing and fate in field. In parallel, respirometric tests were undertaken to evaluate the impact of field ageing on the biodegradation rate. As a result, the use of biodegradable films for vine mulching provide similar agronomical performances as PE; grapevine growth and harvest yield were found to be significantly higher for the mulched modalities than for the bare-soil. This positive mulch-induced effect appeared from the first growing season and was maintained three years later even if the biodegradable mulch started deteriorating 5 months after planting. Thus, in spite of the early loss of integrity of the studied biodegradable mulch films, a significant positive effect on the vine growth, the rootstock development, the earliness of the first harvest and the yield (and quality) of the two first harvests have been evidenced. This leads to reconsider the required life expectancy of mulch film in the case of vineyard and constitutes encouraging results towards the possibility of substituting PE films with biodegradable ones.