Effects of Seed-Placed Hog Manure-Recovered Struvite on Canola Seedling Emergence

Seedling toxicity is a major limitation to P fertilizer rates that can be seed-placed with sensitive crops such as canola (Brassica napus L.). In this growth room bioassay, we tested whether struvite recovered from liquid hog (Sus domesticus L.) manure could improve seedling emergence in canola relative to monoammonium phosphate (MAP) and polymer-coated monoammonium phosphate (CMAP). Twenty canola seeds per pot were planted in two low-P soils (a Gleyed Regosolic sand [Entisol] and an Orthic Black Chernozemic clay loam [Udic Boroll]). The P sources were applied in the seedrow at rates of 7.5 or 15 mg P kg(-1) soil (similar to 25 or 50 kg P2O5 ha(-1)), either at 5.4 or 10.9% seedbed utilization (SBU). Final emergence (percent of seeds planted), emergence rate, and lag were predicted using the Gompertz function. The higher rate of MAP reduced overall seedling emergence by 47% in the clay loam and 34% in the sand while the slow-release P sources, struvite and CMAP, showed no significant evidence of seedling toxicity in either soil. Emergence was 0.6 d faster with struvite than with MAP, regardless of soil or P rate. Averaged across soils, SBUs, and P rates, final emergence decreased in the order: struvite (87%) > CMAP (86%) > MAP (69%), indicating the superiority of struvite and CMAP with respect to seedling toxicity. These results indicate that struvite can be seed-placed at higher rates than those recommended for MAP on canola, with a much lower risk of seedling damage, thereby minimizing yield losses and replanting costs.