Combined effect of biochar and soil moisture on soil chemical properties and microbial community composition in microplastic-contaminated agricultural soil

Accumulation of microplastics (MPs) in agricultural environments has caused growing concern in recent years because of its detrimental impacts on soil quality, crop productivity and ecosystem function. This study was conducted to assess the impact of biochar on soil chemical and microbial properties in a MP-contaminated soil under two moisture regimes. Soil was contaminated with 1% (w/w) of low-density polyethylene MPs. Four types of standard biochar, that is, oil seed rape (OSR) biochar produced at 550 degrees C (OSR 550) and 700 degrees C (OSR 700) and soft wood pellet (SWP) biochar produced at 550 degrees C (SWP 550) and 700 degrees C (SWP 700), were applied at a rate of 5% (w/w). The control was maintained without MP addition. The samples were incubated in soil with two moisture regimes, that is, at 30% and 70% of the water holding capacity, and the soil chemical and microbiological properties were assessed after 100 days of incubation. OSR biochar application significantly increased soil pH (8.53-8.81) and electrical conductivity (0.51-0.58 dS/m) in both moisture regimes. The effect of biochar application on soil enzyme activity and microbial community composition did not show a clear trend. However, SWP 700 biochar improved soil enzyme activity compared with that of the control and improved bacterial diversity and evenness compared with those of other biochars, which was attributed to the high surface area available for microbial colonization. Low soil moisture content significantly reduced enzyme activity and bacterial richness even with biochar amendment, except for SWP 550 biochar. This study implies the suitability of biochar for improvement of soil quality in MP contaminated soil under both moisture regimes. However, further long-term studies are needed to get a clear understanding on the impact of different types of biochar on MP-contaminated soil.

Automated summary

The accumulation of microplastics (MPs) in agricultural environments has raised concerns due to its negative impacts on soil quality, crop productivity, and ecosystem function. This study aimed to investigate the effects of biochar on soil chemical and microbial properties in a MP-contaminated soil under different moisture regimes. The results showed that the application of biochar increased soil pH and electrical conductivity, but had no clear trend on soil enzyme activity and microbial community composition. However, a specific type of biochar improved soil enzyme activity and bacterial diversity compared to other biochars. Low soil moisture content reduced enzyme activity and bacterial richness, but this effect was mitigated by the addition of biochar.