Development and evaluation of an organically certifiable growth medium for cultivation of cyanobacteria

Abstract

On-farm cultivation of phototrophic, N-fixing cyanobacteria, grown in raceway ponds, could provide organic farmers an alternative N source to meet crop fertilizer needs. The application of cyanobacterial fertilizer in certified organic agriculture requires a growth medium of certified organic ingredients. This study compared growth and N-fixation of cyanobacteria cultured in two media, Allen and Arnon (AA) and a growth medium of organic-approved ingredients (RB) developed by the authors. A xenic culture of Anabaena sp. was grown for 2 weeks in the laboratory. The RB medium had significantly lower concentrations of P, Fe, B, Zn, and Cu than the AA medium. Cyanobacteria grown in RB had significantly greater exponential growth rate but significantly lower net total Kjeldahl nitrogen (TKN) than those grown in AA. In a follow-up replicated field study, the xenic culture of Anabaena sp. was inoculated into raceways aerated by paddle wheels. There was no significant difference in exponential or linear growth rate between the two treatments though the RB medium had lower concentrations of P, Co, Zn, and B than the AA medium. The lack of difference could be the result of an overarching limiting factor evident in both treatments such as light or C depletion or that the lower nutrient concentrations in RB were still sufficient for growth and N-fixation. There was no difference in net TKN between the two treatments, suggesting similar rates of N-fixation. Since bone meal contributed trace amounts of N to the RB media, it is possible that maximal N-fixation was not achieved. However, RB medium was able to support growth similar to that of the AA medium in raceway cultivation.