Title: Designing relevant biochars as soil amendments using lignocellulosic and manure-based feedstocks Authors
Submitted to: Journal of Soils and Sediments
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 10, 2013
Publication Date: March 21, 2013
Citation: Novak, J.M., Cantrell, K.B., Watts, D.W., Busscher, W.J., Johnson, M. 2013. Designing relevant biochars as soil amendments using lignocellulosic and manure-based feedstocks. Journal of Soils and Sediments. 14:330-343. Interpretive Summary: Biochar is a byproduct of the biofuel processing industry. Biochar has a long history as a soil amendment; however, it doesn’t always work effectively to improve soil fertility. Biochar's effectiveness as a soil amendment varies considerably with feedstock selection and production conditions. It would be a more successful soil amendment if the biochar was engineered to have certain chemical properties that are known before soil application. Here, we conducted a laboratory incubation study using biochars produced from agricultural crop and nutshell waste, along with poultry manures. In addition, we made biochars from blends of several agricultural waste materials by mixing them in known ratios with poultry manure. These biochars were laboratory incubated in a sandy soil for 2 to 4 months, and about every month the soils were leached with water. Soil and the leachates were analyzed for their nutrient concentrations. We found that biochar produced from pine chips did not significantly increase soil fertility or nutrients released into leachates. Biochars produced from poultry litter, in contrast, greatly increased nutrient concentrations in the soil and leachates. We also found that biochar blends cause the soil to contain sufficient soil nutrient concentrations without losing much into the leachate. These results imply that biochars can be produced through blending feedstocks that can more effectively improve soil fertility levels.
Technical Abstract: Biochars contain an assemblage of organic and inorganic compounds; they can be used as an amendment for carbon sequestration and soil quality improvement. Not all biochars are viable soil amendments, however, because of differences in their chemical composition. In this study, we demonstrate how biochars can be designed with relevant properties as successful soil amendments through feedstock selection, pyrolysis conditions, and particle size choices. Biochars were produced by pyrolysis of parent lignocellulosic (peanut hulls, pecan shells, switchgrass, pine chips, hardwood wastes wood), and manure (poultry litter) feedstock sources, as well as blends of these feedstocks at temperatures ranging from 250 to 700 degrees Celisus (°C). Additionally, blended feedstocks were made into greater than 2-millimeter (mm) pellets prior to pyrolysis at 350°C. Dust sized (less than 0.42 mm) biochar was obtained through grinding of pelletized biochars. After chemical characterization, the biochars were evaluated as fertility amendments in a Norfolk soil. Poultry litter biochars were alkaline and enriched in nitrogen and phosphorus (P), whereas biochar from lignocellulosic feedstocks exhibited mixed pH and nutrient contents. Blending poultry litter with pine chips resulted in lower biochar pH values and nutrient contents. In soil incubations experiments, all biochars significantly raised soil pH, soil organic carbon, cation exchange capacity, and Mehlich 1 extractable phosphorus and potassium. Poultry litter biochar added at 20 grams per kilogram resulted in excessive soil P concentrations (393 to 714 milligrams per kilogram) and leachate enriched with dissolved phosphorus (22 to 70 milligrams per liter). Blended and pelletized poultry litter with pine chip feedstock reduced soil pH and extractable soil P and potassium concentrations. Water leachate dissolved P concentrations were significantly reduced through blending. This study revealed that biochars and blended biochars can have different impacts at modifying soil quality characteristics.