A Long Term Trial Evaluating Nitrogen Recovery of Applied Dairy Manure By Three Forage Species.

Efficiency of manure nitrogen use can best be evaluated in long term trials where N recovery of both newly applied and historically applied manure N can be evaluated. This long-term study compares recovery of N from surface applied dairy slurry and fertilizer by three perennial grasses: perennial ryegrass (Lolium perenne L.), orchardgrass (Dactylis glomerata L.) and tall fescue (Festuca arundinacea Schreb.). The experimental site was established in 1996 with surface-banded dairy slurry and commercial fertilizer applied to a tall fescue stand. Both manure and fertilizer were applied in four equal applications beginning in late March and then after the 1st, 2nd and 3rd of four annual harvests. The original tall fescue stand was ploughed down in 2003 and plots of tall fescue, perennial ryegrass or orchardgrass were seeded. Manure and fertilizer treatments continued from 2004-2010 and included total annual N rates of 194 or 388 kg ha-1 as ammonium nitrate (Fert-low and Fert-high), and 351 or 676 kg ha-1 as dairy slurry (Man-low and Man-high). Apparent nitrogen recovery (ANR) was calculated as ‘(N uptake - N uptake by control)/N applied’. Orchardgrass had significantly higher ANR than tall fescue and perennial ryegrass for both fertilizer treatments, with the highest value of 0.70 for Fert-low. Tall fescue had significantly higher ANR rates than the other two grasses with both manure treatments. Perennial ryegrass ANR was substantially lower than the other grasses and this may be attributed to lower ryegrass yields