Phosphorus losses from low-emission slurry spreading techniques

Low emission slurry spreading techniques are known to improve nitrogen use efficiency, but their impact on phosphorus (P) losses in surface runoffhas received little attention. the current study was designed to examine the effect of slurry spreading technique on P losses in runoff. Twelve treatments were examined on 0.5- m by 1.0- m plots in a nominal 2 × 6 factorial design experiment. Treatments comprised grass swards at two different stages of growth, a stubble and a 4-wk regrowth, and six different slurry application treatments: control (no slurry), and slurry applied to simulate splash-plate, injection (across and down slope), and trailing shoe (across and down slope) spreading. Slurry was applied by hand (40 m³ ha^-1). Rainfall simulations (40 mm h^-1) were conducted at 2, 9, and 28 d post-slurry application. When slurry was applied to the stubble, dissolved reactive P (DRP) concentrations in runoffat Day 2 were 47 and 37% lower (P < 0.05) from the injection and trailing shoe treatments compared with the splash-plate treatment. Similarly, at Day 2, TP concentrations in runofffrom the injection treatments were 27% lower (P < 0.05) than the splash-plate treatment. In contrast, application technique had no effect (P > 0.05) on P concentrations in runofffollowing slurry application to the regrowth treatment. Phosphorus concentrations in runoffwere unaffected by direction of slurry spreading (across or down) at both applications. Our results indicate that trailing shoe and injection techniques offer the potential to reduce DRP concentrations in runoffduring the period immediately aft er slurry application.