Biochar-induced soil stability influences phosphorus retention in a temperate agricultural soil

Abstract

Surface runoff from agricultural fields is the largest non-point source of phosphorus (P) that pollutes surface water in humid temperate regions. Best management practices have attempted to reduce P loading and improve P retention in agricultural soils, but significant losses continue to occur, emphasizing the need for novel solutions. The objective of this study was to determine whether wood-based biochars applied to an agricultural field, 3 years earlier, could reduce P loss in surface runoff by increasing water infiltration or by improving soil stability. Field plots amended with Dynamotive, Basques and Pyrovac biochars (5 and 10 t ha−1) or without biochar were subjected to 30-min of simulated rainfall to determine runoff volume, time-until-ponding, infiltration rate, and water holding capacity, as well as the P concentration and P load in runoff. The distribution of soil macro- and micro-aggregates and their total organic C and total P content was measured. Soil water dynamics were not affected by biochar amendments, however, runoff contained significantly less ortho-P in field soil amended with Dynamotive and Basques biochar at 5 t ha−1 and significantly less particulate P when amended with biochar at 10 t ha−1. Biochar-amended soil had significantly greater microaggregate stability, organic C and total P content than the control soil without biochar. The reduction in particulate P concentration in runoff may be the result of biochar integration within the microaggregate structure, which indirectly promotes P retention in macroaggregates.