Biochar addition to soil highly increases P retention and decreases the risk of phosphate contamination of waters

Abstract

Phosphorus loss from agricultural soils is an important cause of eutrophication. The diversity of soil conditions and biochar feedstocks induces various effects on P retention after biochar application. Here, the effect of biochars at three application rates (0/1/5%, w/w) on P sorption and desorption in paddy soil with two levels of P application, 0 and 60 mg kg−1, were evaluated. Results show a notable reduction of the phosphorus activation coefficient (PAC, AP (available P)/TP (total P)) with biochar addition, thus suppressing the risk of P loss by the formation of Ca–P and Fe–P. The Langmuir sorption maximum (Qm) increased by 20.7–21.6%, 18.5–40.6% and 14.1–31.2% in amendments of biochar obtained from pig manure, corn straw and pine, respectively. The P sorption index (PSI) and maximum buffer capacity (MBC) in soils with biochar obtained from different feedstocks ranged in order from pig manure > corn straw > pine. Pig manure biochar had no significant effect on P retention due to changes in Ca/Mg/P by adjusting the pH, electronegativity and P content, resulting in anion repulsion. However, pine-derived biochar was favorable for the accumulation of thermally stable carbon dominated by aromatic carbon as well as lower alkalinity, promoting P sorption and suppressing P availability, especially at low P levels. In this study, we show that adding woody biochar to soil can simultaneously suppress nonpoint source pollution and reduce P fertilizer inputs.