Phosphorus Fertilization of Ryegrass with Ten Precisely Prepared Manure Biochars

Biochars made from livestock manures need to be better understood in relation to their high nutrient contents. Accordingly, the objective of this investigation was to assess the plant availability and agronomic efficacy of phosphorus (P) contained within chemical fertilization compared to the P contained in ten precisely prepared and characterized manure-derived biochars. Two identical greenhouse experiments were conducted using ryegrass (Lolium multiflorum Lam.). The ten biochars were created from dairy, swine, beef, turkey, and chicken manures. Each manure feedstock was converted into biochar at two temperatures (350°C and 700°C). The soil was a sand (Uchee series; loamy, kaolinitic, thermic Arenic Kanhapludults) with a low P content. The biochar-amended treatments received P on a basis of 50 mg P₂O₅ kg^-1 soil. The biochar treatments were compared to chemically fertilized treatments of 0 to 150 mg P kg^-1 soil. The biochars did not contain yield-limiting levels of EC, pH, Zn, or Cu. Phosphorus in the manure-derived biochars was readily plant available. The biochars generally produced ryegrass yields similar to chemical fertilizer. The chicken 350°C biochar produced the highest ryegrass yield, and the swine 350°C biochar produced the lowest ryegrass yield. For the biochar treatments, the ryegrass Cu and Zn concentrations were within normal ranges, and they were not significantly different from the simple chemical fertilization treatments. Thus, for ryegrass growth, manure biochars can be used for their P-supplying capacities. This can be important to manure management, crop fertilization, and conservation of global P resources.