Continuous and Substantial Reduction of Ammonia Volatilization Under the Coexistence of Microplastics and Biochar : Annual Observation of a Rice-Wheat Paddy-Upland Rotation Soil System

Biochar (BC) has obtained widespread attention as an agricultural ammonia (NH3) abatement conditioner. Meanwhile, microplastics (MPs) are verified to affect the fate of NH3 . However, the impacts and mechanisms of MPs coupled with BC on NH3 losses in rice and wheat soils are mostly untapped. The aim of this study was to investigate the mechanisms of common MPs (i.e. , polyethylene, polyester, and polyacrylonitrile) and straw-derived BC on NH3 losses in rice-wheat rotation soils. Results showed that BC alone and MPs with BC (MPs+BC) reduced 5.5% and 11.2–26.6% cumulative NH3 volatilization than the control (CK), respectively, in the rice season, with increased nitrate concentration and soil cation exchange capacity being the dominant contributors. BC and MPs+BC persistently reduced 44.5% and 60.0–62.6% NH3 losses than CK in the wheat season as influenced by pH and nitrate concentration. Moreover, BC and MPs+BC increased humic acid abundance by 159.1 and 179.6% than CK, respectively, in rice and wheat seasons. The adsorption on soil ammonium roots and the promotion of crop root growth by humic acid were the main causes of NH3 reduction. Our findings partially revealed the mechanisms of the coexistence of MPs and BC on NH3 mitigation in rice-wheat rotational ecosystems