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

Soil-biodegradable mulch films are designed to be incorporated into the soil at the end of the crop cycle, to be degraded by soil microorganisms. Despite growing scientific interest, open-field studies about the fate of these mulch films in soils are rare, with most research conducted in laboratories. We performed an open-field trial to evaluate the effects of soil incorporation of both a combining a commercial soil-biodegradable mulch film and broccoli and sorghum crop residues over two cropping seasons. The mulch film was sampled after broccoli harvesting and placed inside mesh bags that were buried horizontally or vertically at different depths. Film biodegradation was assessed by direct (CO2 emissions) and indirect indicators (film mass and area loss). Three experiments were conducted to evaluate (a) how incorporating crop residues affect mulch film degradation; (b) temporal changes of soil microbial activity after the incorporation of crop residues and mulch films; and (c) possible bias in the measurement of soil CO2 emissions due to horizontal vs. vertical mesh bag orientation. Incorporation of crop residues enhanced mulch film degradation and increased the soil esterase activity. However, abundance of soil fungi and bacteria in bulk soil was not increased by mulch film presence. Mesh bag orientation did not alter the soil CO2 efflux or affect the degradation degree of mulch films. Film in mesh bags buried at 10–15 cm depth showed greater degradation than those buried at 0–5 cm. Further in-field studies are necessary to evaluate the effects of soil incorporation of residue from different crops and impacts of other associated management practices such as various soil tillage regimes.