Phosphorus (P) is an essential crop nutrient. Dwindling phosphate rock reserves essential for P fertilizer manufacture are increasingly necessitating P recovery from waste and its recycling in fertilizer products. Struvite (MgNH4.PO4.6H2O), which is a slow-release fertilizer recovered from wastewater, holds potential as an alternative P fertilizer helping to close the P loop, particularly in organic crop production where soil P deficiency is pronounced. Research is needed to explore options for enhancing the dissolution dynamics of struvite and improving crop response, particularly in alkaline soils. Therefore, this thesis evaluated struvite for its capacity to supply plant-available P as affected by soil and different crop species in common crop rotations in the Canadian prairies. Field experiments conducted on alkaline soils in southern Manitoba under organic management examined the effect of struvite application timing and preceding green manure crop species on wheat crop response. A complementary growth room bioassay examined mechanisms controlling struvite-P mobilization as affected by struvite application timing and the presence of a buckwheat crop. Results from the field study demonstrated variability in responses of green manure species to struvite and the yield of a subsequent spring wheat crop. Response to struvite application was greater for buckwheat compared to field pea and faba bean. However, this differential response did not translate to a greater subsequent wheat crop response following struvite application to buckwheat. Applying struvite to the preceding green manures, compared to applying to the wheat crop did not produce a significant agronomic response in the wheat crop. Results from the growth room bioassay indicated no significant impact of a buckwheat crop on the availability to a subsequent crop of struvite-P applied to the buckwheat. Pre-seeding P application led to decreased cumulative P uptake by buckwheat from MAP relative to the at-seeding application of MAP but had no impact on P uptake from struvite. Our results suggest a lower agronomic response to struvite relative to MAP, regardless of timing of application. Although buckwheat appeared to be efficient in mobilizing struvite P, it may not effectively transfer sufficient P to support the growth of a following crop.

Keywords: Soil phosphorus, organic farming, alkaline soils, monoammonium phosphate