Biochars Impact On Phosphorus and Potassium Release Into Soil and Water Leachates.

Biochar can improve soil fertility levels because they contain P and K. There is limited information, however, on quantities of P and K released from biochars made from different feedstocks, pyrolysis conditions, and after application to different soil types. This study evaluated the impact of biochars made from manure, grasses, wood, and agricultural residues using two different processes (pyrolysis, hydrothermal carbonization) on P and K concentrations in soil and water leachates. Biochars were mixed at 0, < 1 and 2% (w/w) into two sandy Coastal Plain soils (an Ultisol and Entisol) and a silt loam glacial till soil (Mollisol). The treatments were laboratory incubated and were leached several times with deionized water. Soil and water leachate P and K concentrations varied greatly between biochar application rates, pyrolysis conditions, feedstock, and soil type. More P and K leached through the sands than the silt loam soil. Biochar made from manure significantly increased soil and water leachate concentrations of P and K, but biochars made from wood, grasses, and shell wastes did not affect P and K concentrations. This studied revealed that the biochars elemental and water soluble P and K concentrations were highly variable and that the two sands were prone to P and K leaching losses.