The application of mineral fertilizer nitrogen (N) is a quick and convenient way of supplying N to grassland. It is the primary way in which farmers can manipulate grass DM production within a grazing system, as it ensures an adequate supply of N is available to allow grass to reach its full potential yield. Two field-plot studies were carried out on perennial ryegrass swards at two different sites with different soil types (sandy loam and clay loam) in southern Ireland between 2004 and 2006. Their purpose was to examine the effect of various fertilizer N application strategies on grass dry matter (DM) production in spring and throughout the main growing season and also on N uptake, N recovery and N concentration in grass applied with fertilizer N. Application rate and application date of fertilizer nitrogen (N) are important factors determining grass production response and N recovery by grassland in spring. Study (1) was conducted at two sites in spring 2005 and 2006. In comparison with a non-fertilized (zero–N) control, urea N was applied at rates of 60 and 90 kg N/ha either as single or split applications on eight dates ranging between 11 January and 14 March in both years. Grass was harvested on four occasions between 21 February and 25 April, also in both years. Split fertilizer N applications provided the best outcome in terms of grass DM production, apparent recovery of fertilizer N (ARFN) and cost of additional grass produced compared with single applications. Likewise, in this study the optimum date to commence fertilizer N application was 21 January combined with a second application on 26 February in terms of the cost effectiveness of the fertilizer N input to increase grass DM production. In grassland it is typically recommended that fertilizer N is applied immediately after defoliation in each grazing/cutting rotation throughout the year. In practice, farmers often deviate from this approach with a ‘blanket’ approach on farms where fertilizer N is applied once per rotation; i.e. fertilizer N is applied to swards at different stages of regrowth across the farm. Study (2) was conducted at two sites in 2004 and 2005. Fertilizer N was applied on 24 occasions throughout each growing season. There were three sets of plots at each site with each set receiving applications of fertilizer N eight times and harvested eight times per year. Fertilizer N application to each set was offset by approximately 10 days following the start of the experiment each spring with overlapping harvests of each set throughout each growing season. Two fertilizer N application strategies were compared: (i) application immediately after each harvest (IAH) in each rotation and (ii) a blanket application once per rotation, which was xvi represented by the mean outcome of fertilizer N applied at different stages of regrowth (SOR): IAH, early to mid-rotation (EM) and mid to late rotation (ML). Two types of fertilizer N; Calcium ammonium nitrate (CAN) and urea were applied at annual rates of 200 and 300 kg N/ha. Swards were harvested at four week intervals until mid-August, at five week intervals until mid-September and at six to eight week intervals for harvests from mid-October to late November. Fertilizer application strategy, type and rate all had a significant (P≤0.001) effect on grass dry matter (DM) production. CAN produced higher annual DM yields than urea and differences were greatest during the spring and early summer. Applying fertilizer IAH produced the highest DM yields except where urea was applied at a rate of 300 kg N/ha. A blanket approach to fertilizer N application can be integrated into an annual fertilizer N application strategy between mid-January and mid-March and from July onwards with little or no loss of production provided that fertilizer N is applied IAH at the other time of the year. These studies work in conjunction to highlight some of the advantages and disadvantages of the use of mineral N fertilizer in pasture-based systems of production in Ireland. The results obtained can be used co-ordinate a planned, season long, approach to fertilizer N application that can optimize the return in terms of grass DM production whilst at the same time minimize the loss of N to the surrounding environment. This co-ordinated plan highlights three key aspects, (i) that initial fertilizer N applications in spring should involve two smaller applications spread apart from each other rather than one large one, (ii) that there is an appropriate fertilizer type to use at different times of the year and finally (iii) that fertilizer N can be applied using a blanket approach in the first two rounds in spring and the last two rounds in autumn without any negative impact on productivity.
|Publication status||Unpublished - 2019|
- Irish grassland, Nitrogen fertilizer