Submitted to: Frontiers in Sustainable Food Systems
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/10/2018
Publication Date: 9/11/2018
Citation: Novak, J.M., Spokas, K.A., Johnson, M.G. 2018. Concentration and release of phosphorus and potassium from lignocellulosic and manure-based biochars from fertilizer reuse. Frontiers in Sustainable Food Systems. https://doi.org/10.3389/fsufs.2018.00054.
DOI: https://doi.org/10.3389/fsufs.2018.00054

Interpretive Summary: Pyrolysis of organic feedstocks produces a solid-product called biochar. Many types of organic feedstocks are suitable materials to produce biochars, including-animal manures, wood waste compounds, green-wastes, and other plant-based materials. Biochars are composed of organic and inorganic compounds, consequently, they can be used as soil amendments to increase organic matter and soil plant nutrient contents. A concern with the use of biochar as a soil fertility amendment, however, are vast differences in their nutrient composition. For example, biochars produced from hardwoods and softwoods generally have lower concentrations of phosphorus (P) and potassium (K) as compared to biochar from poultry litter. This has caused a concern that certain biochar types may not be particularly effective at increasing soil nutrient levels. Thus, we conducted an experiment to compare which biochar-types (hardwood versus poultry litter) will release more P and K amounts, and subsequently increase soil plant available P and K concentrations. After incubating biochars in a sandy soil, we found that biochars produced from poultry litter release much higher P and K contents and increased plant available P and K concentrations compared to hardwood biochar. These results highlight the importance of choosing the appropriate feedstock for biochar production since there were significant differences in P and K released into soil.

Technical Abstract: Biochars pyrolyzed from plant residues and animal manure feedstocks may contain disproportionate amounts of phosphorus (P) and potassium (K). Unequal nutrient characteristics can impact the biochars ability to properly supply as well as improve soil P and K fertility levels. A soil incubation study was performed to test the hypotheses that biochar produced from poultry litter will release more water soluble dissolved P (DP) and K (DK) concentrations and would also increase soil plant available P and K concentrations as compared to lignocellulosic-based biochars. Biochar was pyrolyzed at 500 degrees Celsius from hardwood waste products (HW), pine chips (PC), poultry litter (PL), and an 80:20 pine chip/poultry litter blend, which were then added at 20 grams per kilogram to a sandy soil. Un-amended (no biochar) Norfolk E soil served as a control. During the incubation, all treatments were leached four times with deionized water and the leachate analyzed for DP and DK; their concentration and mass released as a function of total amounts present were then calculated. At the study’s conclusion, soils were extracted using Mehlich-1 reagent for determination of plant-available P and K concentrations. Leachates from soil amended with 100% PL biochar and the 80:20 blend had significantly more DP and DK mass (59 and 1018 mg, respectively) released compared to PC and hardwood biochars (0.07 and 23 mg). Significant amounts of DP were released from PL biochar with additional water leaching, but DK release results were mixed. Soil Mehlich-1 P and K contents were significantly increased using PL biochar compared to lignocellulosic-based biochars. Blending PC with PL feedstocks at 80:20 weight ratio reduced Mehlich-1 soil P concentrations to 35 milligrams per kilograms, which was more aligned with soil test P levels recommended for a corn (Zea mays) production in southeastern USA Coastal Plain sandy soils. These results reveal that 100% PL biochar offers a higher potential to provide more P and K to soils than lignocellulosic-based biochars, and that feedstock blends can be used to create designer biochars that align soil test fertilizer values with plant nutrient requirements.