2019 ASHS Annual Conference

Plastic film mulches are often used in horticulture to manage weeds, improve water retention, and increase the soil temperature. Currently, bioplastics and biofabrics are being investigated as sustainable alternatives to plastic film. However, there are few effective biodegradable mulches in compliance with National Organic Program (NOP) certification guidelines. Polylactic acid (PLA) is a 100% biobased polymer (a requirement of the NOP) that could be incorporated into the soil after a field season, unlike bioplastics. However, PLA does degrade slower than other biodegradable polymers, which brings its NOP eligibility into question. A novel biodegradable PLA-based mulch with wood fiber particles embedded in the melt-blown matrix (3M Company; St. Paul, Minnesota, USA) was compared to a MaterBi bioplastic mulch film (Bio360, Dubois Agrinovation; St. Remi, QC, Canada) across two climatically diverse locations (Scottsbluff, NE and Lincoln, NE) in a two-year mulch degradation trial. Five soil amendments which included compost, compost extract, cover crops, fallow irrigation, and a combination of the four (“kitchen sink”) were applied with the goal of accelerating the rate of mulch degradation (and compared to a null control). Our objectives were to determine the individual and combined effects of soil amendment treatments and residual mulch in soil on vegetable crop yield, soil organic matter, macronutrient availability, and soil physical properties. Compost amendment (alone and in “kitchen sink” treatments) increased crop yield by 34%-43%, soil sorptivity up to 18.6%, and macronutrient availability compared to all other treatments at Scottsbluff. Soil incorporation of the PLA-based mulch combined with application of all amendments (“kitchen sink”) increased soil sorptivity by 9.5% at Lincoln compared to the PLA-based mulch with no application. The MaterBi-based mulch lost 91% of its initial mass after 1 yr in Lincoln, whereas the PLA-based mulch lost 63% of its initial mass in 1 yr. The degradation rate was slower at Scottsbluff (semi-arid climate and coarse-textured, low organic matter soil) for the MaterBi-based mulch (32% mass loss) than in Lincoln (humid continental climate and high organic matter soil), but the PLA-based mulch mass loss was similar (67%). Initial results of this study suggest that the effects of biobased mulch residues on soil properties and yield are negligible compared to the effects of compost application; moreover, site-specific conditions and mulch properties are more important drivers of mulch biodegradation than soil management.