Biodegradable plastic film mulch increased nitrous oxide emissions in organic leek but decreased emissions in organic cabbages

<title>Abstract</title> Plastic film mulch (PFM) controls weeds and increases yields, making them attractive to vegetable growers; biodegradable PFMs potentially reduce the harms associated with conventional PFMs. PFMs increase soil biological activity, accelerating the decomposition of soil organic matter and potentially increasing emissions of some greenhouse gases (GHGs). Conversely, they are a barrier to rainfall infiltration and gas exchange, reducing harmful nitrate (NO₃⁻) leaching and ammonia (NH₃) volatilisation. The effects of PFMs on the processes resulting in GHG emissions are not well explored outside conventionally grown commodity crops in major growing regions. To address this, we conducted a field plot-scale experiment on an organic vegetable farm in SW Wales (UK). We measured nitrous oxide (N₂O), methane (CH₄), carbon dioxide (CO₂) and potential NH₃ emission from the soil, growing leeks or cabbages, with or without biodegradable PFM and amended with poultry manure or green-waste compost. Averaged across both crops, yield was 26% higher with PFM; potential NH₃ emissions were 18% lower (43% on a yield-scaled basis) in mulched treatments than unmulched; CH₄ emissions were not significantly affected. Yield-scaled N₂O emissions were 62% higher in mulched leeks than unmulched but 56% lower in mulched cabbages than unmulched; this coincided with higher soil NO₃⁻ concentrations in mulched leeks than either unmulched crop or mulched cabbages. Results were not obtained for CO₂, so partial global warming potential (GWP) and greenhouse gas intensity (GHGI) were determined mainly by N₂O emissions. Thus, biodegradable PFM is potentially useful in reducing harmful gaseous N emissions in organic horticulture.