Biochar phosphorus fertilizer effects on soil phosphorus availability

Abstract

Biochar is a potential material for making slow-releasing phosphorus (P) fertilizers for the sake of increasing soil P use efficiency and mitigating P losses. However, the long-term effects of P-laden biochars on soil P availability remains unconcerned. In this study, a laboratory-scale 70-days soil incubation experiment was conducted to study the effects of original and P-laden biochars on soil P availability and fractions. Two original biochars were derived from maize stalks by pyrolyzing at 350 °C and 600 °C. P was laden on those biochars by immersing biochars in saturated KH₂PO₄ solution for 24 h. Eight treatments were set for the incubation experiment, which were soil, soil + triple-superphosphate (TSP), soil + 350 °C biochar, soil + 600 °C biochar, soil + TSP + 350 °C biochar, soil + TSP + 600 °C biochar, soil + 350 °C P-laden biochar, and soil + 600 °C P-laden biochar. Results showed that original biochars could decrease soil available P through P adsorption. And there were no significant differences of soil P fractions under the treatments of mineral P fertilizer and P-laden biochars. Whereas, compared to mineral P fertilizer, P-laden biochars, especially 600 °C P-laden biochar, could maintain soil available P in a significantly higher level across the incubation. It was mainly because of the slow-releasing pattern of P laden on biochar and a more homogeneous soil P source distribution under P-laden biochar treatments. These results indicated that P-laden biochar could work as P fertilizer to improve soil P use efficiency.

Keywords: Intra-biochar diffusion; Mineral P fertilizer; P-laden biochar; Phyto-available P; Slow-releasing.