Biochar Soil Amendment to Save Water and Enhance Vegetable Productivity

Biochar is a carbon-based product similar to charcoal increasingly produced and marketed as an organic soil amendment.  Biochar is created through pyrolysis, superheating organic biomass (such as wood) in an enclosed environment with limited oxygen to produce bio oils, heat energy, and biochar.  As pyrolysis industries grow and expand, there is increasing opportunity to utilize locally produced biochar for its value in sustainable agriculture.  In 2014, a greenhouse trial was performed to identify optimal pyrolysis production temperatures and soil application rates to conduct subsequent field studies.  Lettuce (Parris Island Cos) was used due to its short growing season and compact size.  The lettuce was grown in 3-gallon plastic pots filled with silt loam field soil, and amended with 4-4-4 organic fertilizer and biochar made from Utah-sourced cherry wood.  We evaluated three pyrolysis temperatures (375 °C, 475 °C, and 575 °C), three application rates (1%, 2%, and 3% by weight), and two particle sizes.  Mean weight (g) of plants was determined in a single harvest nine weeks after seeding.  Variation in plant weight within and among treatments was high; likely caused by inconsistent irrigation due to emitter malfunction on several occasions, and defoliation by caterpillars.  Lettuce growth was decreased with the addition of biochar in all treatments except 375 °C, which is a common short term observation in similar studies.  Soil amended with biochar produced at 375 °C, pulverized, and applied at the 2% rate produced the largest lettuce.  In 2015, we will test biochar for enhancement of tomato and melon growth and yield at four cooperating vegetable farms and evaluate its protection of tomato roots from a common soil disease, phytophthora root rot.  We anticipate that biochar amendment will enhance plant growth and yield, and may reduce plant water needs in these longer-term field studies.