Identifying strategies to improve nitrogen use in grazing dairy systems
Maintaining or increasing milk production whilst simultaneously reducing the environmental footprint of dairying (both from a greenhouse gas and nutrient loss perspective) is a key goal for the long term future of the Irish dairy industry. Perennial ryegrass white clover swards (at 23% annual sward white clover content) have been shown to increase both milk production per cow (+ 48 kg milk solids per cow) and herbage production (+ 1.2 t DM/ha) over a number of years compared with perennial ryegrass-only swards in the Clonakilty Agricultural College systems experiment at a stocking rate of 2.75 cows/ha and high levels of nitrogen fertilizer (250 kg/ha per year). However, the persistency of white clover has been shown to be negatively correlated to high nitrogen fertilizer levels and there is a requirement to further investigate how a reduction in nitrogen fertilizer use will affect performance in intensive dairy systems (i.e. stocking rate > 2.5 cows/ha) utilising perennial ryegrass-white clover swards and also perennial ryegrass-only swards. The objective of this project is to investigate strategies to improve nitrogen use in dairy systems, specifically in relation to sward type (i.e. perennial ryegrass-only and perennial ryegrass-white clover) and nitrogen fertilizer level (225, 150 and 75 kg nitrogen/ha per year).
Overall Project Objective
The objective of this project is to use meta-analytical methods, a systems experiment and component plot work to identify strategies to reduce nitrogen fertilizer use in dairy systems. The specific objective of the systems experiment in Clonakilty Agricultural College is to assess the biological efficiency of perennial ryegrass-only and perennial ryegrass-white clover swards receiving varying fertiliser rates of 225, 150 or 75 kg nitrogen/ha per year, giving 4 grazing treatments a perennial ryegrass-only sward receiving 225 kg nitrogen/ha, a perennial ryegrass-only sward receiving 150 kg nitrogen/ha, a perennial ryegrass-white clover sward receiving 150 kg nitrogen/ha and a perennial ryegrass-white clover sward receiving 75 kg nitrogen/ha.
This experiment will describe treatment effects in terms of:
- Milk production performance (per cow and per hectare)
- Herbage growth and utilization
- Economic performance, greenhouse gas and nutrient footprints
This project will use both a systems experiment and component plot work to identify strategies to reduce nitrogen use in dairy systems. The farm systems experiment will use a randomized design with 4 grazing treatments, a perennial ryegrass-only sward receiving 225 kg nitrogen/ha, a perennial ryegrass-only sward receiving 150 kg nitrogen/ha, a perennial ryegrass-white clover sward receiving 150 kg nitrogen/ha and a perennial ryegrass-white clover sward receiving 75 kg nitrogen/ha., comprised of 28 cows each,. Individual animal error will be used to test for differences between treatments. Animals will be randomly allocated to treatments based on breed, parity, genetic merit (Economic Breeding Index), calving date, body weight and body condition score. Each grazing treatment will have a separate farmlet of 20 paddocks and will be stocked at 2.56 cows/ha. Component experiments will be utilized within the framework of the overall systems experiment to gain a greater understanding of the effect of sward type and nitrogen fertilizer on the soil (e.g. nitrogen mineralization), animal (e.g. dry matter intake) and sward (e.g. nutritive value). A plot study investigating a range of nitrogen fertilizer application rates and strategies on white clover swards will also be undertaken.