Establishing release dynamics for plant nutrients from biochar

To assess the value of biochar to direct supply of crop nutrients we considered the release of phosphorus, magnesium and potassium from a hardwood biochar in a sequential leaching experiment with deionized water. Cumulative P release was proportionally large despite being quantitatively small, and the sixth extraction yielded 44–73% of the first, indicating that provision of soil P might be sustained for several seasons. Conversely, K release was quantitatively large but declined rapidly from first extraction to the last (6–18% of the first extraction). Only 6–27% of total Mg was recovered. These results indicate that these elements have contrasting associations with biochar that govern the trajectory and ultimate extent of their release. Fitting cumulative loss curves enabled these patterns to be quantitatively captured and compared and could provide a means to develop predictive capacity for the supply of nutrients from biochar to soil and plant.