Developing struvite as a fertilizer for container grown nursery crops

Morgan Camille Fish

Current commercial sources of phosphorus (P) are mined, nonrenewable, and quickly becoming depleted. Known P resources worldwide could become exhausted within the next 50 years. Struvite, magnesium ammonium phosphate hexahydrate (NH4MgPO4·6H2O), is creating interest as a sustainably produced, recycled fertilizer source. Struvite is a precipitate that forms in the pipes of wastewater systems, causing expensive and damaging blockages. By installing special reactors that purposefully induce precipitate formation, companies have capitalized on P-rich wastewaters to produce struvite precipitates. Inducing precipitation in reactors serves a dual purpose of reducing P content in water systems and producing a P-rich byproduct with potential for use as a slow release P fertilizer. The efficacy of struvite as a P fertilizer in outdoor nursery production of woody plants has yet to be demonstrated. In this research, two representative woody nursery crops, lilac (Syringa vulgaris ‘Mademoiselle Lemoine’), a deciduous shrub, and rhododendron (Rhododendron ‘Roseum Elegans’), an evergreen shrub, were grown in typical Douglas-fir bark-based container substrates using struvite as a P source. The experiment was a factorial combination of three pre-plant P treatments (triple superphosphate (TSP) and struvite at the recommended rate of P and struvite at ½ the recommended rate); applied by three different methods (dibble, incorporate and top dress); in two different growth substrates (100% Douglas-fir bark and 80% Douglas-fir bark: 20% peat moss); with liquid P applied during production a two rates (0 and 100ppm). Plants were grown in #1 (1 gallon containers) outdoors on a gravel nursery bed under overhead sprinkler irrigation. Plant response to treatments was evaluated by measuring end-of-season shoot and root growth and evaluating visual quality. Plant growth responses indicated struvite used as a P fertilizer for container nursery production of lilac and rhododendron in Douglas-fir bark substrates was as effective as the traditionally used phosphorus fertilizer, TSP. Application method had no consistent influence on plant growth. Leaf color results were similar to plant growth responses. The results of this study demonstrated struvite, a recycled and renewable, P source could be an effective replacement for the traditionally used, mined P fertilizer source, when growing woody container crops in Douglas-fir bark based substrates.

Developing struvite as a fertilizer for container grown nursery crops

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