Submitted to: Bioresource Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 21, 2004
Publication Date: July 2, 2004
Citation: Mulbry, W.W., Westhead, E.K., Pizarro, C.X., Sikora, L.J. 2005. Recycling of manure nutrients: use of algal biomass from dairy manure treatment as a slow release fertilizer. Bioresource Technology. 96:451-458. Interpretive Summary: The vulnerability of aquatic ecosystems and groundwater to nutrient pollution has forced increasingly stringent environmental regulations to be placed on dairy farms. Production of algae on wastewater nutrients could provide a holistic solution to nutrient management problems on existing farms. Algal biomass recovered from such systems has a variety of potential on- and off-farm uses. Although it has primarily been considered as an alternative high-grade protein source in animal feed, algal biomass with a balanced N:P ratio is a potentially valuable organic fertilizer. The objective of this study was evaluate the use of dried algal biomass as a slow release fertilizer. Soil mineralization tests revealed that only 3% of the algal nitrogen (N) and 60% of algal P were present as plant available N and P at the beginning of the experiment. However, approximately 30% of algal nitrogen (N)and 80% of algal phosphorus (P)was converted to plant available N and P within 21 days at 25 C. Results from cucumber and corn plant growth studies using potting mixes amended with dried algae showed that 20 day-old seedlings contained approximately 16 % and 46 % of the applied algal N and P, respectively. Plants grown with algae-amended potting mixes were equivalent to plants grown with a comparable commercial fertilizer with respect to dry weight and nutrient content.
Technical Abstract: Production of algal biomass using nutrients from animal manures is a potential alternative to the land application of manures. One possible use for the harvested biomass is as a slow release fertilizer. The objective of this study was evaluate the fertilizer value of dried algal biomass that had been grown on anaerobically digested dairy manure. Results from a 42 day flask study using Sassafras and Codorus soils amended with two levels of dried algal biomass showed that approximately 3% of algal nitrogen (N) was present as plant available N at the beginning of the experiment. Approximately 30% of algal N was converted to plant available N within 21 days at 25 oC in both soils. Levels of Mehlich 3 extractable phosphorus (P) in the two soils rose with increasing levels of algal amendment but were also influenced by existing soil P levels. In a phosphorus replete Sassafras soil at the highest loading rate, approximately 60% of algal P was present as Mehlich 3 extractable P at the beginning of the experiment. This value rose to 80% within 21 days. In a phosphorus deficient Codorus soil, approximately 45% of algal P was present as Mehlich 3 extractable P at the beginning of the experiment and this value did not increase significantly with 42 days. Based on these results, plant growth studies were conducted using cucumber and corn seedlings grown in ProMix BX potting mix amended with different levels of dried algae or with comparable levels of a commercially available fertilizer (Garden-tone 4-6-6). Analysis of 20 day-old cucumber and corn seedlings showed that the seedlings grown in algae amended mixes contained 13-20%, 40-60%, and 38-54% of the applied N, estimated available N, and P, respectively. Seedlings grown in fertilizer amended mixes contained 26-41%, 42-65%, and 26-37% of the applied N, estimated available N, and P, respectively. Seedlings grown in algae-amended potting mixes were equivalent to those grown with comparable levels of fertilizer-amended potting mixes with respect to seedling dry weight and nutrient content.