Response of organic grain and forage crops to struvite application in an alkaline soil

Abstract

Struvite (NH4MgPO4·6H2O) may be an appropriate fertilizer to address phosphorus (P) deficiencies in organic cropping systems, but field studies assessing crop response to struvite are lacking. Field experiments were conducted over 3 yr on a low-P, alkaline soil in Manitoba to assess the effect of struvite application rate on the yield and P accumulation of organically managed grain and forage crops. Struvite was applied to spring wheat (Triticum aestivum L.) and flax (Linum usitatissimum L.) at 0, 20, 30, and 40 kg P ha–1 in separate experiments each year and to alfalfa (Medicago sativa L.)–grass forage at 0, 30, 60, and 90 kg P ha–1 in a single application in a 3-yr experiment. Wheat grain yield, P concentration, and P accumulation increased linearly with increasing struvite rate, whereas flax showed little to no response. Forage yield, P concentration, and P accumulation also increased with struvite rate. Benefits to forage yield and P accumulation were greatest in the second year, demonstrating important residual effects of struvite application. Struvite application shifted forage composition to become dominated by alfalfa whereas the unfertilized treatment was dominated by grasses. Annual P recovery efficiency was 4–7% for wheat, 1–2% for flax, and 7–12% for forage and did not vary significantly with struvite application rate. Our findings demonstrate that struvite applied at a relatively high rate is an effective P source for wheat and alfalfa-based forage under organic management, but not for flax.