Comparison of Techniques for Quantification of Total Inorganic Elements in Biochar.

The use of biochar as soil amendment for production of agronomic and horticultural crops has increased in popularity in recent years because of its potential to increase soil water retention, reduce nutrient leaching and sequester carbon. Often times, routine ashing and acid digestion methods used for plant tissue and soils are utilized for analyzing inorganic elements in biochar. The recalcitrant nature of biochar precludes complete dissolution of the samples when routine soil and plant ashing and digestion procedures are used. Undigested C in the samples interferes with plasma during ICP measurement and results in inaccurate determination of the total elements. Additionally, traditional HF digestion methods occlude certain elements via precipitation. Our objectives are to: 1) compare existing techniques and identify an efficient method that accurately determines the elemental composition of biochar and 2) evaluate the efficiency of methods across various biochar properties. Five different techniques are used: 1) X-ray fluorescence; 2) EPA 3051 microwave digestion method; 3) Ashing at 550 ^oC combined with EPA 3051 microwave digestion method; 4) Nitric + perchloric acid digestion method; and 5) Ashing combined with nitric + perchloric acid digestion method. Ten biochars variously produced from wood, corn stover, switch grass, and alfalfa by both fast and slow pyrolysis at various temperatures are included in the study. Results of the study will be presented and discussed.