Biochar Addition to a Southeastern USA Coastal Sand to Decrease Soil Strength and Improve Soil Quality

Abstract:Southeastern USA coastal plain soils are sandy, compacted, and exposed to a subtropical environment; they are low in organic carbon and have little aggregation. In the past, increasing organic carbon to decrease compaction and improve aggregation has been ineffective because organic matter vanishes within a few months in the warm, wet environment. However, organic carbon in the form of charcoal or biochar is recalcitrant having remained in tropical Amazonian soils for centuries. In a lab experiment, we added non-activated biochar to the Ap horizon of a Norfolk loamy sand, a coastal sandy Acrisol. The Biochar was produced in a retort at 700 degrees C and added to soil at rates of 0, 0.5, 1, and 2 % (w/w). Switchgrass (Panicum virgatum) was also added at rates of 0 and 1 % (w/w). Switchgrass and biochar amendments did not show any consistently significant improvements for aggregation or water holding capacities. Soils treated with both amendments had higher infiltration rates than those without amendments. Soil cone indices as a measure of compaction were lower for the higher level of biochar added; biochar showed a relationship of decreasing soil strength with increasing biochar content. Biochar also increased soil carbon contents. Though the biochar did not improve all soil properties, it sequestered carbon and reduced soil strength, two of the more difficult problems to ameliorate in coastal plain soils