2017 ASHS Annual Conference

The main advantage of biodegradable mulches (BDMs) in agriculture is they can be tilled into the soil after use, saving time and labor for growers, and eliminating disposal issues for communities. Biodegradation of BDMs in the soil can be inferred by the presence or absence of visible mulch fragments; although this is not a direct measure of biodegradation, it provides an initial assessment of mulch biodegradation. Three experiments were designed to develop a protocol for measuring BDM fragments in the soil following soil-incorporation of mulch. Experiment 1 (carried out at Mount Vernon, WA, and Knoxville, TN) included five BDMs, and a polyethylene (PE) mulch reference plot (Mount Vernon only). Pumpkin was planted at both locations, and mulches were tilled into the soil after harvest. Mulch recovered (%) was calculated based on the surface area of the soil cores taken per plot. Only 59% of mulch fragments were recovered from the reference plot. BDM recovery was 13% to 54% at Mount Vernon and 0% to 72% at Knoxville. There was high plot-to-plot variation by treatment (3% to 95% at Mount Vernon, 2% to 88% at Knoxville). In Experiments 2 and 3 (Mount Vernon only), one BDM was laid, then tilled into the soil immediately to prevent deterioration. In Experiment 2, 15 samples were collected per plot, resulting in 70% recovery of mulch. In Experiment 3, 128 samples were collected per plot, and 62% of mulch was recovered. In summary, sampling with a relatively large core recovered less than 59% of tilled-in PE mulch, there was high variability between plots within each treatment, and 50 cores minimum per plot would be needed to estimate mulch remaining in the field. Thus, soil sampling with a large core method was ineffective, and new sampling methods are needed to assess BDM remaining after soil incorporation.