The objectives of this work were to determine the effects of initiating application of fertilizer nitrogen (N) to winter wheat at different growth stages (GSs) on grain yield and N use efficiency (NUE). A factorial experiment was carried out in two growing seasons (2011 and 2012) with five timings of first N application (GS 24/26 [tillering], GS 30, GS 31, GS 32 or GS 37) and an unfertilized control, two sowing densities (100 and 400 seeds/m 2 ) and a cattle slurry treatment (with or without slurry). The latter was included to simulate variation in soil N supply (SNS). Delaying the first application of N from the tillering stage until GS 30 had no significant effect on grain yield in either year. Further delaying the initial N application until GS 31 caused a significant yield reduction in 2011, in comparison to GS 30 application, but not in 2012. Differences in efficiency of recovery and use of fertilizer N by the crop among the first three application timings were small. There was no evidence to support alteration in the timing of the first application of N in response to low plant density. Slurry application did not influence SNS, so the interaction between SNS and fertilizer N application timing could not be determined. It is concluded that in order to maximise yield and NUE, the first N application should be applied to winter wheat between late tillering and GS 30 and that delaying the first N until GS 31 can lead to yield reductions compared to the yield obtained with earlier application.

Peatlands are a dominant component of the Irish landscape comprising some 20% of the total land area (Connolly & Holden, 2009). These ecosystems have been greatly impacted by anthropogenic activity with Renou-Wilson et al. (2011) estimating that 80% of Irish peatlands have been disturbed due to peat cutting, horticulture, afforestation and conversion to agricultural use. Bord na Móna (a semi-state-owned company) manages 100,000 ha of peatland (Fitzgerald, 2006) with approximately 4 million tonnes of peat produced per year (Malone & O'Connell, 2009). In 2015, the company produced 547,428 tonnes of horticultural peat from a peatland area of 2,872 ha (Charles Shier, personal communication). Horticultural peat is also produced by private sector companies, and although the extent is uncertain, an estimate of production can be taken from Renou-Wilson et al. (2011) who reported that, in 2003, Irish peat moss producers sold an estimated 650,000 tonnes (assuming a bulk density of 4 t m −3 ) of horticultural-grade peat.Peat extraction is associated with both in situ and ex situ processes and activities that lead to degradation and greenhouse