Microplastics persist in an arable soil but do not affect soil microbial biomass, enzyme activities, and crop yield

Abstract

Background: Microplastics (MP, plastic particles <5 mm) are ubiquitous in arable soils due to significant inputs via organic fertilizers, sewage sludges, and plastic mulches. However, knowledge of typical MP loadings, their fate, and ecological impacts on arable soils is limited. Aims:We studied (1) MP background concentrations, (2) the fate of added conventional and biodegradable MP, and (3) effects of MP in combination with organic fertilizers on microbial abundance and activity associated with carbon (C) cycling, and crop yields in an arable soil.Methods: On a conventionally managed soil (Luvisol, silt loam), we arranged plots in a randomized complete block design with the following MP treatments (none, lowdensity polyethylene [LDPE], a blend of poly(lactic acid) and poly(butylene adipate-coterephthalate) [PLA/PBAT]) and organic fertilizers (none, compost, digestate). We added 20 kg MP ha -1 and 10 t organic fertilizers ha -1 . We measured concentrations of MP in the soil, microbiological indicators of C cycling (microbial biomass and enzyme activities), and crop yields over 1.5 years.Results: Background concentration of MP in the top 10 cm was 296 ± 110 (mean ± standard error) particles <0.5 mm per kg soil, with polypropylene, polystyrene, and polyethylene as the main polymers. Added LDPE and PLA/PBAT particles showed no changes in number and particle size over time. MP did not affect the soil microbiological indicators of C cycling or crop yields.Conclusions: Numerous MP occur in arable soils, suggesting diffuse MP entry into soils.In addition to conventional MP, biodegradable MP may persist under field conditions.However, MP at current concentrations are not expected to affect C turnover and crop yield.

Soil science challenges—An interdisciplinary overview of current and future topics

“…Schöpfer et al. (2022), in this issue, found ≈ 300 plastic particles < 0.5 mm per kg in an agricultural soil that had not been treated with any of the materials listed above. They concluded that there are diffuse sources of microplastic that have not been identified so far.…”