Effect of Biochar on Available Phosphorus Status in Alfisols Derived from Charnockite in Ekiti State, Nigeria

Biochar, a carbon-rich product of pyrolyzed biomass, has been used as an amend- ment to improve the properties of marginal highly-weathered soils in the tropics characterized by widespread phosphorus (P) deficiency. Alfisols derived from charnockite in Ekiti State are typically deficient in available phosphorus. Two alfisols from Ire-Ekiti and Ijan-Ekiti were amended with 0 (P-only), 5, 10 and 20% (w/w) biochars from maize stover (mB) and sawmill waste (sB) and incubat- ed for 56 days with the addition of 60 mg kg-1 P in solution and a control without biochar and P-solution. Incubated soils were sampled fortnightly and analyzed for available P using Mehlich III extractant, pH, and electrical conductivity (EC) in water (1:2 w/v). Results show that biochar increased the soil pH by 1-2 units and EC from the native 0.02 to 8.37 dS m-1 with mB at 10 and 20%, causing soil salinity (EC > four dS m-1). Biochar increased available P to values ranging from 9.96 to 376.22 mg kg-1 compared to 2.93 to 7.64 mg kg-1 in control and 5.42 to 40.13 mg kg-1 in P-only treatments. The available P increased with days of incu- bation up to day 42 and followed by a slight decline, but the P in biochar-treated soils was significantly higher than other treatments. The mB significantly im- proved soil properties (soil pH, EC, and available P status), particularly at higher rates more than sB. The 5% mB in which the problem of salinity problem associ- ated with higher rates is avoided should be recommended.