Utilizing Biochar to Mitigate Nitrate Leaching and Increase Crop Yield in South Central WA

A field study was conducted to analyze the impact of biochar as a soil amendment to corn crop yields in a region where flood irrigating is still commonly practiced. Groundwater nitrate contamination poses health and environmental risks in the Lower Yakima Valley located in south central Washington State, where those disproportionately affected are primarily of American Indian or Hispanic descent in this rural, agricultural community. The dominant agricultural practices in this region (CAFOs, hops, corn, wheat, and spearmint) are thought to be the major contributors to the elevated nitrate levels in groundwater. Biochar is known to adsorb nitrate at a rate of 11 ppm per 0.75 grams of biochar in a laboratory setting. It is unknown how a field test setting will impact crop yields in this regional setting. Ten research plots (each 400 sq ft) were randomly distributed within a 1-acre field planted with sweet corn (2 control plots: no biochar, 4 low biochar concentration plots: 20 gallons/100 sq ft, 4 high concentration biochar plots: 80 gallons/100 sq ft). Biochar was evenly mixed into the upper 4 inches of soil in the high and low concentration research plots. Fertilizer was applied to the entire 1-acre field at a rate of 200 pounds per acre at the time of planting and then a second application when plants reached six inches in height. Root mass development of corn and soil moisture increased while soil pH decreased with increasing concentration of biochar in topsoil. Low concentration plots had a 20% increase in yield and high concentration plots had a 26% increase compared to the control plots (yield defined as total number of ears available and biomass). Biochar is an effective additive for combating excess nitrate leaching that will potentially appeal to agribusiness due to the substantial increases in crop yields documented in this study.