Degradation Rate of Bio-based Agricultural Mulch is Influenced by Mulch Composition and Biostimulant Application

Spunbond polylactic acid (PLA) based agricultural mulches provide several benefits including environmental sustainability, durability, weed control, and soil moisture conservation. Large-scale adoption of PLA mulches in organic and conventional agricultural systems has been limited due to slow to biodegradation and persistence in soil. A 16-week microcosm study was conducted to assess the effects of four commercially available biostimulants (Biocat 1000, Extract PBA, Custom GP, and Environoc 501), a compost extract, and distilled water, urea, and sucrose controls on biodegradation and microbial respiration of bio-based mulch in soil. Mulch treatments included a spunbond PLA mulch, two novel composite PLA mulches with alfalfa (PLA-A) and soy (PLA-S) particles embedded in the fabric, paper mulch, and bio-based plastic film. After 16 weeks, the PLA-A and PLA-S mulches lost 43% and 48% more mass than the PLA mulch. Cumulative microbial respiration in the PLA-A and PLA-S mulch microcosms was 245% and 239% greater than respiration in PLA mulch microcosms. The effects of biostimulants on biodegradation and microbial respiration were inconsistent. Our results suggest that composite spunbond PLA mulches containing plant-based materials degrade more quickly than pure PLA mulches in soil, and certain biostimulant products may accelerate biodegradation.