Biochar addition to soil highly increases P retention and decreases the risk of phosphate contamination of waters
2019
Xu, Min | Wu, Jun | Yang, Gang | Zhang, Xiaohong | Peng, Hong | Yu, Xiaoyu | Xiao, Yinlong | Qi, Hui
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.
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