Submitted to: Journal of Vegetable Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/20/2006
Publication Date: 7/25/2007
Citation: Mulbry III, W.W., Kondrad, S.L., Pizarro, C. 2007. Biofertilizers from Algal Treatment of Dairy and Swine Manure Effluents: Characterization of Algal Biomass as a Slow Release Fertilizer. Journal of Vegetable Science. 12(4):107-125. 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 to evaluate the fertilizer value of algae that had been grown in laboratory (indoor) and pilot scale (outdoor) algal turf scrubbers using raw dairy manure effluent, anaerobically digested dairy manure effluent, and raw swine manure effluent. Results suggest that there are only minor differences in the fertilizer value of algae grown using the difference manure effluents. Soil mineralization tests revealed that only 5% of the algal nitrogen (N)was present as plant available N at the beginning of the experiment. After 21 and 63 days, the total algal N present as mineral N increased to 25-29% and 36-41%, respectively. Approximately 40% of total algal P was present as plant available P throughout the 63-day incubations. Results from corn plant growth studies using potting mixes amended with dried algae showed that 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: An alternative practice to land spreading of manure effluents is to grow crops of algae on the nitrogen (N) and phosphorus (P) present in these liquid slurries. The overall environmental and economic values of this approach depend, in part, on the use and value of the resulting algal byproduct. Among the potential uses of algal biomass from such systems is its use as a slow release fertilizer. The objective of this study was to evaluate the fertilizer value of algae that had been grown in laboratory (indoor) and pilot scale (outdoor) algal turf scrubbers using raw dairy manure effluent, anaerobically digested dairy manure effluent, and raw swine manure effluent for vegetable production. Results from a multifactorial N-mineralization experiment using soil amended with eight algal biomass treatments showed that approximately 5% of total algal N was present as plant available N at day 0. After 21 and 63 days, the total algal N present as mineral N increased to 25-29% and 36-41%, respectively. Approximately 40% of total algal P was present as Mehlich-3 extractable P throughout the 63-day incubations. Results from plant growth experiments showed that 17 day-old corn (Zea mays L.) seedlings grown in algae-amended potting mixes were equivalent to those grown with comparable levels of fertilizer-amended potting mixes with respect to shoot dry weight and nutrient content. There were no differences in the fertilizer value of different batches of algae at the low rate amendment (~ 47 kg of available N per ha). However, at the high rate amendment (~ 93 kg of available N per ha) shoot biomass, and shoot N and P contents were greatest for treatments containing algae grown using indoor laboratory scale ATS units and least for treatments with algae grown outdoors using pilot scale ATS units. Longer term field studies are needed to assess the effect of algal biomass amendment on corn and vegetable yields under a range of growth conditions.