Every coin has two sides: Continuous and substantial reduction of ammonia volatilization under the coexistence of microplastics and biochar in an annual observation of rice-wheat rotation system

Abstract

Microplastics (MPs) are verified to affect the fate of ammonia (NH₃) in agricultural soils. However, the impacts and mechanisms of MPs coupled with biochar (BC), a widely used agricultural conditioner, on NH₃ losses 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 volatilization 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. The increased nitrate concentration and soil cation exchange capacity were dominant contributors to the reduced soil NH₃ volatilization in the rice season. 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-like substances in soil dissolved organic matter by an average of 159.1 % and 179.6 % than CK, respectively, in rice and wheat seasons. The increased adsorption of soil NH₄⁺ and the promotion of crop root growth were the main mechanisms of NH₃ reduction. Our findings partially revealed the mechanisms of the coexistence of MPs and BC on NH₃ mitigation in rice-wheat rotational ecosystems.

Keywords: Biochar; Dissolved organic matter; Microplastics; Rice-wheat rotation; Soil ammonia volatilization.