Feasibility of biochar production and utilization at a farm-scale: a case-study in non-irrigated seed production

Despite many demonstrated benefits that biochars can have on agricultural soils, there are few examples of profitable biochar utilization on commercial farms. Barriers to profitable utilization include successfully pairing waste streams, biochar production facilities, and farms where biochar is utilized. Farm-scale biochar systems, which utilize agricultural wastes as feedstocks and produce energy and biochar for on-farm use, may therefore have efficiency advantages over industrial biochar producers in pairing these components. However, two critical uncertainties are 1) whether a biochar can be produced from on-farm feedstocks with appropriate qualities for soil amendment, and 2) whether on-farm feedstocks are sufficiently abundant to meet on-farm demand. Here we evaluate these issues for a farm-scale gasification system in NE Washington State that produces biochar from grass seed screenings and straw. Field trials to evaluate the biochar as a liming alternative found it was highly effective when broadcast at a rate of at least 18 Mg ha-1. Biochar outperformed hydrated lime in the first year of the study, increased soil moisture and microbial abundance, and improved yields by 290% across both years. While the seed screening biochar had an excellent fit for soil requirements, estimated production could provide only enough biochar to amend <3% of the production area annually. Additional biochar produced from straw feedstock could increase the total amended area to 6.3 – 11.8% of the production area annually, translating to a return interval of 9-16 years. We conclude that biochar production from on-farm feedstocks approaches or fully meets on-farm demand for liming amendments.