Effect of mulching on soil properties, microbial diversity and activities, and crop yield

Abstract Aims - Plastic films are used to mulch soils to control weeds, especially in organic farming. Their application leaves persistent plastic fragments in soils, with poorly understood environmental and health consequences. Plant fiber textiles (bio-canvas) are promising alternatives since they are more persistent than straw mulching and are entirely biodegradable. Hemp fibers are particularly interesting materials due to their renowned resistance, allelopathic and trophic properties for soil life. However, their effects on soil microbiota and yield remain unclear. Methods - In a greenhouse experiment, we assessed the effect of soil mulching (bare soil control, plastic mulch, hemp straw mulching, hemp-canvas) on lettuce growth, soil climatic conditions, enzymatic activities and microbial communities (bacteria and fungi). Our experiment allowed to distinguish effects associated to mulching, being i) the homogeneity of soil covering (plastic mulch and hemp canvas) or not (control, hemp mulch), ii) the biodegradability (hemp mulch, hemp canvas) or not (control, plastic mulch), and iii) their interaction. Results - An interaction occurred between cover homogeneity and biodegradability when using the hemp canvas, leading to higher soil relative water content, stable soil temperature, higher laccase and arylamidase activities, and different soil microbial community structures and fungal diversity, with comparable lettuce yields to that obtained with plastic mulch. Plastic cover induced higher soil temperatures, lower enzymatic activities, and different soil microbial community structures. Conclusions - We conclude that hemp canvas secures lettuce yields, but through different mechanisms compared to plastic mulch, notably via a biostimulating effect on soil microbial diversity and functioning.