Phosphorus availability from magnesium‐modified P‐enriched Douglas fir biochar as a controlled release fertilizer

Abstract

Phosphorus (P) is one of the essential elements required for plant growth and development. However, worldwide, many agricultural soils can be deficient in P. The use of fertilizers and manures as a source of P can be costly, limited in supply in some regions of the world and ecologically unfavorable. Nutrient enriched biochar has been suggested as a relatively cost‐effective and eco‐friendly P source. This study investigated P availability from Douglas fir biochar modified with magnesium chloride and potassium hydroxide solutions only (B), and P enriched modified Douglas fir biochar B50, B100, and B150 corresponding to B treated with 50, 100, and 150 mg P L‐1 solutions of potassium phosphate monobasic. Triple super phosphate fertilizer (FC), and a control treatment without phosphate added (C) used as a reference treatment. Treatments were added to soil in varied amounts to obtain the same P rate of 30 kg P ha‐1. Above ground biomass dry weight yield (R2 = 0.7), and plant height (R2 = 0.86) improved with P contents. After harvest, residual soil P for the FC treatment was significantly greater than all other treatments (P‐value = 1.7848 E‐6, R2 = 0.8). Plant height and aboveground dry weight biomass was greater with B150 compared to B50 at the same total P loading, suggesting that the greater P concentration of the biochar (B150) resulted in less tightly bound P and was therefore more available for plant uptake. This study showed promise of utilizing P enriched Douglas fir biochar as a slow‐release P fertilizer.