Legacy Effects of Biodegradable Mulch and Soil Amendments on Vegetable Crops and the Soil

Plastic film mulches are used in horticulture to manage weeds, improve water retention, and increase soil temperature. Bioplastics and biofabrics are potentially sustainable alternatives to plastic film; however, they have different rates of in soil degradation. Polylactic acid (PLA) is a 100% biobased polymer that degrades slowly, but could fulfill organic certification to be soil incorporated. Mater-Bi is a commercially available biodegradable plastic (bioplastic), which degrades quickly, but cannot be incorporated in organic systems. Our objectives were to determine the individual and combined effects of soil amendments and residual mulch on vegetable crop yield and soil fertility. In a two-year study across two climatically diverse locations, a novel biodegradable PLA-based mulch with embedded wood fiber particles was compared to MaterBi bioplastic mulch after soil incorporation. Four soil amendments, compost, compost extract, cover crops, and a combination of the three, were applied with the goal of accelerating the rate of mulch degradation. Compost amendment significantly increased sweet corn yield by 34-43% and macronutrient availability in 2018 (N-71%, P-75%, K-16.9%) compared to all other treatments at Scottsbluff. Biomulch residues in soil did not influence sweet corn crop yield (p\u3c0.05). Cabbage yield increased in compost treatments in 2019 at Lincoln (p=.0045), and decreased in plots with cover crops (p\u3c0.0001). Soil tensile strength, wet aggregate stability, sorptivity, and compaction were measured 6 and 18 months after soil incorporation of mulch. The PLA biofabric increased water stable macroaggregates compared to the control at both locations in the spring of 2019, whereas the bioplastic decreased macroaggregates compared to the control at Lincoln. Organic amendments improved soil sorptivity both years at Scottsbluff and in 2019 at Lincoln. Initial results of this study suggest that the effects of biobased mulch residues on soil macronutrients and yield are inconsequential compared to the effects of compost application. Biodegradable PLA based mulches may have a positive effect on soil properties after soil incorporation, although they are slow to degrade even with added amendments. Advisor: Samuel E. Wortma