Plastic mulching in agriculture—Friend or foe of N2O emissions?

Polyethylene (PE) mulching is a very common method in agriculture worldwide because the use of PE films can improve product quality and yield by mitigating extreme weather changes, optimizing growth conditions and extending the growing season. Other than the problem with disposal of the plastics hardly any other of its effects on the environment are known. To determine whether covering fields with PE films affects N2O emission, we conducted two experiments: first, comparing N2O emissions of furrows and PE-mulched ridges of a radish field which had received different amounts of N fertilizer and second, assessing whether PE mulching increases N2O emissions from PE-mulched ridges in comparison to non-PE-mulched ridges and furrows of a non-fertilized field. To achieve those aims we took comparative closed chamber measurements in conjunction with a photoacoustic infrared trace gas analyzer during the growing seasons of 2010 and 2011 at a radish and soy bean field site in South Korea. For the radish field site we found significant differences between the N2O emitted by furrows and PE-mulched ridges and found extraordinarily low N2O fluxes from those spots of the ridges which were totally PE-mulch-covered between plant hole openings. At the soy bean field we observed that plant holes of PE-mulched ridges showed only 68% of the emission measured of soils around soy bean plants of non-PE-mulched ridges, implying that PE mulching may decrease N2O emissions. Since our result is contrary to very recent findings we consider the extremely low soil moisture at our sites as explanation for the differences. Because knowledge on how PE mulches affect production and emissions of greenhouse gases is very limited, our study contributes greatly to understanding N2O emission behavior of PE-mulched, poor sandy soils in a temperate monsoon climate.