Effect of dairy manure slurry application in a no-till system on phosphorus runoff

Incorporation of manure slurry under reduced tillage conditions remains a challenge in the northeastern US. New technologies to directly incorporate slurry are available but their agronomic and environmental benefits have generally not been quantified. This study evaluated the effects of five manure slurry application methods on phosphorus (P) loss in runoff (broadcasting with and without incorporation by tillage, shallow disk injection, banded application and aeration, and pressurized injection) and a control (no manure). Research was conducted over a 2 year period in central Pennsylvania on a well-drained Hagerstown silt loam (fine, mixed, semiactive, mesic Typic Hapludalf) under corn (Zea mays L.) production. Approximately 72 h after dairy (Bos Taurus) slurry application (56,000 l ha(-1)) to 10 x 13 m plots, a single rainfall simulation (68 mm h(-1)) was conducted in triplicate on 10 x 2 m areas within the plots. Trends in total P losses in runoff (kg ha(-1)) from plots varied between years and treatments. Aeration yielded lower losses than all other treatments in 2006 and was amongst the lowest in 2007 with losses statistically similar to shallow disk and pressure injection. Remarkably, few differences were apparent in losses of dissolved reactive P between treatments, reflecting high variability in runoff depths. Indeed, variability in runoff depths resulted in some unexpected trends, including high loads from the unamended control and modest loads from the tillage treatment. Results highlight tradeoffs in alternative manure slurry application practices but point to the potential to significantly lower runoff P losses from reduced tillage systems receiving manure slurry.