Biochar Effects On Fertilizer N and P Availability in Soil.

Biochar, a solid by-product from the pyrolysis of biomass, appears to have remarkable agronomic values. It has been reported that biochar has the ability to increases cation retention and phosphate adsorption. An incubation study was carried out in order to study biochar effects on N and P availability using two contrasting Kansas agricultural soils, Eva optima (Eva coarse-loamy, mixed, superactive, mesic aridic haplustalfs) and Morrill Loam (Morrill fine-loamy, mixed, superactive, mesic typic argiudolls). Biochar was obtained from hydrothermal pyroloysis of corn cobs at 305°C with 20 min of retention time. The experimental design used was randomized block design with 4 replications, three biochar rates (0, 2, and 20 g/kg) in combination with either two nitrogen rates (0 and 100 mg/kg) or two phosphorus rates (0 and 20 mg/kg), for a total of 9 treatments. Soils were extracted for Mehlich III P and KCl extractable NO₃-N and NH₄-N at 0, 3, 10, 17, 28, and 56 days following soil amendment. Biochar application at 20 g/kg increased NH₄-N concentrations during the first 10 d and consistently decreased NO₃-N recovery by 5 mg/kg.  Biochar did not affect the recovery of P fertilizer, however, biochar application with N fertilizer increased Mehlich III extractable P in the soil. Although biochar application did not have an overwhelming effect on recovery of N and P fertilizer, the results indicate that biochar amended soils may need additional N following biochar addition.