Soil Phosphorus Fractionation and Bio-Availability in a Calcareous Soil as Affected by Conocarpus Waste Biochar and Its Acidified Derivative

Biochar possesses more profound effects on the availability of soil P in acidic soil than in alkaline and/or calcareous soil, mainly due to P fixation. Therefore, biochar derived from Conocarpus waste (BC) was acidified with sulfuric acid to produce acidified biochar (ABC) and incorporated into a calcareous soil planted with alfalfa in order to investigate P availability and fractionation. Additionally, the changes in some other soil chemical properties were investigated. Both BC and ABC were applied at three rates (0%, 2.5%, and 5%) along with P fertilizer application at four rates (0, 75, 150 and 300 ppm). The results showed that acidification remarkably reduced the pH of ABC by 6.84 units. The application of ABC considerably lowered the soil pH; however, it did not significantly increase P availability in the studied soil. Furthermore, BC, especially at a higher application rate, increased the extractable soil K. Similarly, the amendments increased the soil cation exchangeable capacity (CEC) and soil organic matter (OM), where a profound increase was observed at a higher application rate in the case of soil OM. Similarly, soil-available micronutrients were increased over the control, where a more profound increase was observed in soils treated with ABC. The NaHCO3–P (exchangeable) fraction increased with increasing fertilizer application rate while the residual–P decreased. Therefore, BC and ABC could be used to improve soil quality and enhance soil nutrient availability. However, further studies are required on how to significantly improve soil available P in calcareous soil.