Application Method and Timing Can Increase the NFRV of Cattle Slurry On Grassland.

The trailing shoe application method has been shown to decrease ammonia volatilization from cattle slurry to grassland. The objective of this study was to establish if this translates into increased nitrogen fertilizer replacement value (NFRV) of slurry. We measured the uptake of slurry nitrogen (N) as well as dry matter yield (DMY) in response to mineral N fertilizer in a large scale field experiment for three years on three contrasting grassland sites in Ireland. A randomized block experiment (n=6) was conducted to quantify NFRV as a function of two application timings: April and June; and two application methods: splashplate (SP) and trailing shoe (TS). Grass was harvested seven weeks following SP and TS treatment application. A Michaelis-Menten curve was fitted to the relationship between DM yield and mineral N fertilizer rate on the control treatments. The NFRV of each slurry treatment was calculated from the site, year and timing specific N response curve as the N fertilizer required to obtain a DMY equivalent to that of the slurry treatment, expressed as a percentage of the slurry N applied. Mean NFRVs were higher with TS (April: 32%; June: 15%) than with SP (April: 17%; June: 6%) (P<0.001). Mean NFRVs in April were significantly higher (P<0.001) than in June. We conclude that the expected reduction in ammonia volatilization using TS rather than SP resulted in a measurable increase in the NFRV. However, the timing of slurry application is also an effective way to increase the NFRV.