Ackerman, J. N., Zvomuya, F., Cicek, N. and Flaten, D. 2013. Evaluation of manure-derived struvite as a phosphorus source for canola. Can. J. Plant Sci. 93: 419–424. There is growing interest in the treatment of swine manure to mitigate water quality issues related to phosphorus (P) from livestock operations. Precipitation of P as struvite (MgNH4PO4·6H2O) is a potential strategy to achieve this. The overall objective of this growth room study was to evaluate the effect of manure-derived struvite (MDS) on canola growth and P recovery efficiency. Pure struvite (PS), monoammonium phosphate (MAP), and polymer-coated monoammonium phosphate (PCMAP) were applied to canola plants in plastic pots containing 2 kg of a sandy loam soil. Biomass yields for MDS and PS were similar at all P rates (mean = 7.6 g pot−1) and significantly smaller than those for MAP and PCMAP (mean = 9.3 g pot−1). Differences in P uptake among P sources were detected at the highest P rate where P uptake was significantly greater for MAP and PCMAP (mean = 22.7 mg P pot−1) than for the struvite forms (mean = 16.4 mg P pot−1). Our results show that although P uptake was similar for the struvites and commercial fertilizers at P2O5 rates of 38 mg pot−1 or lower, biomass yield per unit of P taken up was smaller for the struvites. This may be due to lower initial solubility of the struvites in the alkaline (pH 7.7) soil used in this experiment, which gave an early stage growth advantage to canola fertilized with MAP and PCMAP. These results suggest that it may be necessary to supplement struvite with soluble P fertilizers, such as MAP, if applied on soils such as that tested in this study.
Phosphorus removal from agricultural wastewater streams is an important aspect of managing surface water quality, due to the contribution of phosphorus to eutrophication. Removal of phosphorus through struvite precipitation allows for its recovery as a potential fertilizer, and by determining the best conditions for struvite precipitation the removal process can be optimized. The effects of pH, Mg:P ratio, and time on struvite precipitation from anaerobically digested swine manure effluent were investigated. Effluent with Mg:P ratios from 1.0:1 to 1.6:1 were adjusted to pH values between 7.5 and 9.5 and left to equilibrate for 24 h. Results indicate that phosphorus removal increased with increasing pH and Mg:P ratio; the maximum phosphorus removal achieved was 80% at pH 9.0 and a Mg:P ratio of 1.6:1. The purest struvite precipitate was found at pH 7.5, with calcium carbonate and struvite precipitating at higher pH values. A continuously stirred batch of centrate was adjusted to pH 8.4 to determine the struvite formation rate constant. The rate constant was found to be 1.55 h(-1), with 17% phosphorus removal during the first 20 min. The results indicate that struvite precipitation could be a viable method of phosphorus removal from anaerobically digested swine manure.
Dairy farm operations rely on a continuous supply of bedding material for cow comfort and hygiene. The re-use of liquid manure for this purpose has become possible after solid/liquid separation of the manure stream and 24 h processing of the separated solids through a tumbling drum composter. The finished bedding solids are reported to produce superior bedding to regular straw and the separated liquid stream can be retained as crop fertilizer. Off-farm export as bedding is only possible if the material is stable to prevent reheating if bagged or piled. The nutrient value of the retained liquid and the quality of solids for export were investigated on a Canadian dairy farm by examining nitrogen and phosphorus distribution, as well as the self-heating potential of the composted solids. The effect of curing the solids for an additional 4 weeks during both summer and winter operations was evaluated. Results showed that the solids separation and 24 h drum composting process did not result in a compost that could be classified as mature and stable. However, further curing the solid product in ambient temperature piles for 4 weeks reduced compost reheating from 26.2°C above ambient to 7.7°C (winter curing) and 3.8°C (summer curing). Nitrogen and phosphorus analysis revealed little difference between the liquid stream (post solid separation) and the incoming raw manure on a wet weight basis. The use of either of these products as plant fertilizer is similar and solid separation does not impact the agronomic value of the liquid manure. CITATION
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