Microplastics cause environmental problems. Biodegradable plastics have become popular because they aim to avoid such problems. However, their decomposition in the soil may have an impact. This study aims to investigate the effects of biodegradable plastics on the physicochemical properties of soil, specifically the production of CO₂ and N₂O in the soil and plant growth. Three kinds of biodegradable plastics in the forms of 1) nonwoven fabric sheets made of poly-lactic acid (PLA) and polybutylene-succinate (referred to hereafter as fabric), 2) laminate sheets made of polybutylene adipate terephthalate (PBAT) and pulp (hereafter laminate), and 3) drinking cups made of PLA (hereafter cup), were cut into small pieces (<5 mm), added to soil, then water-holding capacity was determined and incubated aerobically for 4 weeks at 30°C in the dark. Soil and gas samples were collected weekly to measure soil pH, nitrate-nitrogen content, CO₂, and N₂O productions. These plastics were also tested in a pot experiment with Komatsuna (Brassica napa var. perviridis). We tested for seed germination, plant growth, leaf color, and fresh weight at harvest. Results showed that the water retention capacity was higher in the fabric plastics as compared to the cup plastics and the control. Soil pH with the fabric plastics dropped during the initial 2 weeks of incubation, then recovered to a similar pH to the control (without plastic). Nitrate contents in the soil with laminate plastics were lower than those in the control, while CO₂ production in the soil with the laminate plastics was higher than that in the control and the other plastics during the incubation period, and even higher than the one of added plastic-C. N₂O was produced rapidly within 1 week of incubation in the soil with the laminate plastics, and cumulative N₂O production from incubation was more than that of the control. The seed germination and plant growth tended to be suppressed in the pot experiment with the fabric and laminate plastics. The results indicate that the influence of these biodegradable plastics on soil properties, greenhouse gas production, and plant growth on the kind of plastic and the timing.

Long-term unregulated mining of ion-adsorption clays (IAC) in China has resulted in severe ecological destruction and created large areas of wasteland in dire need of rehabilitation. Soil amendment and revegetation are two important means of rehabilitation of IAC mining wasteland. In this study, we used sludge biochar prepared by pyrolysis of municipal sewage sludge as a soil ameliorant, selected alfalfa as a revegetation plant, and conducted pot trials in a climate-controlled chamber. We investigated the effects of alfalfa revegetation, sludge biochar amendment, and their combined amendment on soil physicochemical properties in soil from an IAC mining wasteland as well as the impact of sludge biochar on plant growth. At the same time, we also assessed the impacts of these amendments on the soil microbial community by means of the Illumina Miseq sequences method. Results showed that alfalfa revegetation and sludge biochar both improved soil physicochemical properties and microbial community structure. When alfalfa revegetation and sludge biochar amendment were combined, we detected additive effects on the improvement of soil physicochemical properties as well as increases in the richness and diversity of bacterial and fungal communities. Redundancy analyses suggested that alfalfa revegetation and sludge biochar amendment significantly affected soil microbial community structure. Critical environmental factors consisted of soil available K, pH, organic matter, carbon–nitrogen ratio, bulk density, and total porosity. Sludge biochar amendment significantly promoted the growth of alfalfa and changed its root morphology. Combining alfalfa the revegetation with sludge biochar amendment may serve to not only achieve the revegetation of IAC mining wasteland, but also address the challenge of municipal sludge disposal by making the waste profitable.