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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·ha−1). However, at the high rate amendment (-93 kg of available N·ha−1) shoot biomass, and shoot N and P contents were greatest for treatments containing algae grown using indoor laboratory scale algal turf scrubbers (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.
