Biochar-mediated soil phosphorus leaching and distribution behaviors in AWD paddy fields of a Northeast China alluvial plain

Biochar has been recognized to deliver several benefits in field crops. However, its impact on phosphorus (P) leaching, distribution, and deep migration in paddy fields under alternate wetting and drying (AWD) irrigation remains unclear, especially in a typical alluvial plain. A 2-year field experiment was conducted with three treatments: continuous flooding irrigation without biochar, AWD without biochar, and AWD with 20 t ha −1 maize straw biochar. A multi-layer device together with a bottom-sealed polyvinyl chloride bucket was used to monitor dissolved P dynamics and P leaching. And a four-stroke gasoline-powered soil sampler was employed to collect data on the distribution and migration of soil available P and total P along the 0–200 cm soil profile. The shift from continuous flooding irrigation to AWD reduced water percolation by 25 %-38 % but increased soil available P deep migration (100–200 cm). Under AWD, biochar addition further decreased water percolation by 9 % and reduced dissolved P leaching by 20 % compared with AWD alone. Moreover, biochar increased soil available P by 141–277 % and total P migration by 133–219 % at 0–40 cm and while inhibiting the deep migration of soil available P by 119 %-1114 % and that of total P by 210 %-2644 %. The reduced soil available P deep migration with biochar was mainly caused by the decreased soil total P in the 100–200 cm soil profile. Our results provide a novel approach for sustainable P management in agricultural ecosystems, offering critical insights into the role of biochar in regulating nutrient dynamics in paddy soils. • Alternate wetting and drying irrigation (AWD) reduced phosphorus (P) leaching. • AWD promoted soil available P migration to deeper (100–200 cm) soil layers. • Biochar addition lowered P leaching and addressed AWD-induced P deep migration.