The main aim of this study was to investigate how phosphorous (P) release would change after the addition of combined sinfluence upon soil properties sugarcane residuesderived biochar (B) and P fertilizer in a calcareous clay loam soil after 7 and 120 days of incubation. Biochar was produced from sugarcane residues (S) at the temperature of 400°C under limited oxygen condition. A full-factorial experiment was performed in a completely randomized design to evaluate the effects of amendment (without amendment, 1% S, and 1% B) and P (0 and 50 mg kg −1) on availability and P release characteristics over incubation period (7 and 120 days). After incubation, the kinetics of P release in soils was determined by successive extraction with Olsen solution in a period of 2 to 768 h at 25 ± 1°C. Results showed that the difference between cumulative P release in soil treated with S and B, at two incubation times, was not significant (P > 0.05). At both times, the cumulative P release increased by 5 up to 23% as influenced by amendments and P fertilizer. Difference between treatments at 7 and 120 days of incubation was not significant (P > 0.05). The lowest and highest initial amount of P release was found in control soil (14.62 mg kg −1 h −1) and soil treated with P + B (38.26 mg kg −1 h −1), respectively. The maximum and minimum rates of P release were in control soil (0.328 (mg kg −1) −1) and soil treated with P + B (0.203 (mg kg −1) −1), respectively. Also, the lowest and highest initial release rates were observed in control soil (4.79) and soil treated with P + B (7.76), respectively. Biochar addition to soil treated with P increased initial amount of P release and initial release rate of P. Therefore, addition of sugarcane residues-derived biochar to soil treated with P fertilizer can increase P availability in similar calcareous soils.

Biochar has the potential to affect the cycle of phosphorus (P), but the underlying mechanisms of its effects remain poorly understood in calcareous soils. Our understanding of the effects of biochar is limited in calcareous soils during incubation. Therefore, this study was conducted to investigate how the availability and mineral fractions of P change after the addition of combined biochar and P fertilizer during incubation in calcareous soil. Sugarcane residue (raw SR) and biochar (400 °C for 2 h) were added to soils treated with 50 mg kg −1 of P, in the form of Ca(H 2 PO 4) 2 •H 2 O, at 0.5 and 1% (w/w). The soils were incubated at 25 ± 1 °C for 120 days. Available P (Olsen P) contents and mineral P fractions were measured after various incubation times (7, 30, 90, and 120 days). Biochar addition remarkably increased the amount of available P when compared with the raw SR treatment and the control condition (P < 0.05). After 30 days of incubation, the amount of available P in the soils decreased and remained unchanged thereafter. The results indicated that the addition of 50 mg kg −1 of P as fertilizer significantly augmented the labile P and P associated with Fe and Al in all the treatments at all incubation times (P < 0.05). In comparison with P treated with raw SR, P associated with Fe and Al was significantly enhanced after biochar addition (P < 0.05). Significant correlations were found for available P with labile P and P associated with Fe and Al. We found that biochar addition could increase available pools, thus improving available P concentrations at various incubation times. Therefore, we conclude that sugarcane residue biochar can enhance the available P in calcareous soils.