The Effect of Biochar on Root Growth of Large Crabgrass

Biochar is a carbon-rich residue similar to charcoal that is incorporated into the soil to increase nutrient retention and water holding capacity, which in turn increases crop productivity, as well as to sequester carbon. Biochar can increase plant productivity but relatively little is known about the effect of biochar on root growth. We assessed the effect of biochar on large crabgrass (Digitaria sanguinalis L. Scop.), a common weed, grown in rhizotrons under growth chamber conditions. Soil mixed with or without biochar was placed between two clear acrylic sheets in either a full or split design. In the full design, rhizotrons were filled with unamended soil or soil amended with 2% biochar (wt/wt). In the split design, amended and unamended field soil, each occupying half of the rhizotron vertically, was used. Biochar produced at 450°C from two different feedstocks was used. The nutrient rich biochar was produced from a mixture of loblolly pine and switchgrass. The nutrient poor biochar was produced from a mixture of pine, fir, and spruce. At 38 days after transplant, the rhizotrons were scanned with a flatbed scanner, and plants were harvested. Plant height, tiller number, and component dry weight (root, leaf, shoot) were measured. In the solid design, both types of biochar increased the number of tillers produced by large crabgrass. The nutrient rich biochar reduced the partitioning of biomass to roots relative to the nutrient poor biochar and the unamended soil. When grown in the split design rhizotron, large crabgrass root dry weight was greater in the side amended with biochar, regardless of the type of feedstock. These results suggest that biochar can have a significant effect on root growth.