Use of biochar as a possible means of minimizing phosphate fixation and external P requirement of acidic soil

Abstract

Phosphate fixation is a main factor limiting phosphate availability and reducing crop production in acidic soils. Although biochar addition has been suggested as a means of ameliorating acidic soils, questions remain about the impacts of biochar on phosphate fixation and availability in these soils. To address these questions, a biochar produced from sugarcane bagasse was added at four different levels (0, 1, 3, and 6% w/w) to an acidic soil. After 30 days of incubation, comparisons were made between the chemical properties of the biochar-amended soils and those of the original one. Sorption isotherm experiments were also conducted to estimate soil phosphate sorption capacity and affinity parameters under biochar amendment. Results showed that biochar application improved such soil chemical properties as pH and cation exchange capacity as well as exchangeable calcium, magnesium, sodium, and potassium cations. Biochar was also observed to increase phosphate sorption capacity of the soil but reduce its phosphate sorption strength, indicating that biochar-amended soils were potentially able to fix lower amounts of phosphate than the original acidic soil was. Moreover, soil phosphate buffering capacity indices decreased as a result of biochar incorporation, indicating the easier release of phosphate from the solid to the solution phase in biochar-amended soils. Biochar addition was also observed to reduce effectively (up to 62%) the standard phosphorus requirement of the soil. In conclusion, biochar amendment was found to induce positive changes in phosphate sorption properties of acidic soils, thereby providing conditions more favorable to plant growth through sufficient phosphate availability.