|Abstract or Summary
- Algae have shown great potential as a source for renewable fuels. However, current production schemes have not been able to prove a sustainable energy return on investment due in part to the high costs of nutrient addition and the energy required for drying the biomass. Integrated algae-dairy production systems have been posited as a potential solution for algal production barriers as well as a way to capture environmentally problematic nutrients excreted by animals in concentrated animal feeding operations. As the organic food industry grows, so will the need for organic nitrogen (N) fertilizers. Algal meal, the high protein co-product of algal biodiesel production, could help meet this need. This work has two objectives: 1) to quantify the fertilizer value of algal meal relative to an organic N fertilizer, feather meal, and a conventional standard, urea; 2) to show that utilizing the fertilizer value of algal meal at $800 Mg⁻¹ will allow an integrated dairy-anaerobic digester-algae production facility to be an economically viable manure management system. A laboratory incubation was carried out to characterize carbon (C) and N mineralization of two different algal meal products. The N mineralization rate, C respiration rate, and impact on pH and soluble salts were the same for feather meal and one of the algal meals. A field trial was conducted to assess the overall crop productivity of corn grown with algal meal fertilizer, feather meal, and urea. There was no significant difference in corn ear yield or ear N uptake among any of the algal meal treatment rates (101 kg N ha⁻¹, 146 kg N ha⁻¹, 190 kg N ha⁻¹) and the high rate of feather meal or urea (190 kg N ha⁻¹) application. These results indicate that algal meal is an effective N fertilizer that should be valued relative to feather meal on a price per unit of nutrient basis. Considering environmental benefits and current policy incentives, assigning a fertilizer value of algal meal of $800 Mg⁻¹ for a 7-3-1 product adds enough income to make an integrated dairy-anaerobic digester-algae system an economically viable, sustainable farm-energy production system.