Influence of Pecan Biochar on Physical Properties of a Norfolk Loamy Sand

Abstract

Because the southeastern US Coastal Plain has high temperatures and abundant rainfall, its sandy soils have poor physical characteristics and low carbon (C) contents. To increase soil C, we added switchgrass (Panicum virgatum) and nonactivated recalcitrant pecan biochar. Biochar was developed by pyrolyzing ground pecan shells at 700 °C. Biochar had 88% C, 0.4% N (C:N ratio, 220:1); 58% of its C resided in polymerized aromatic ring structures. Biochar treatments were 0, 5, 10, or 20 g kg−1 of soil, which was the Ap horizon of a Norfolk loamy sand, a thermic Typic Kandiudult. Switchgrass was ground to a fine powder and added to the biochar treatments at rates of 0 or 10 g kg−1. Treatments were incubated in 750-g columns for 70 days at 10% (wt wt−1) water content. Biochar decreased soil penetration resistance; adding switchgrass also decreased it by the end of the experiment. Biochar and switchgrass affected aggregation, infiltration, and water-holding capacity; but results were mixed. Although the nonactivated biochar (and switchgrass) improved some soil physical characteristics, other biochar formulations may have more of an effect on soil properties.