The evaluation of environmental, agronomic and economic implications of high and low input dairy systems.

End of Project ReportThis report marks the end of the first phase of a long term systems trial on phosphorus. The objective of the work was to define the minimum soil P necessary to ensure optimum production in terms of milk. If phosphorus applications are minimised, the potential damage to the environment is minimised. Three herds (21 cows each) were managed on three separate farmlets. The objective was to have each herd graze on land with it’s own soil P level. The target soil P levels required for herds 1, 2 and 3, were Indices 1, 2 and 3, respectively. At the end of this phase of the work these soil P targets were achieved. These were achieved by using no P fertiliser on treatment 1, application of maintenance P on treatment 2 (14kg p/ha) and 28 kg P/ha on treatment 3. In the course of the four years, grass growth, silage yields, milk yields and composition, cow weights and body scores were recorded. Soil phosphorus levels changed slowly. It took between 20 and 40 kg P/ha to move Morgan’s P by one unit. Silage yields and grazing sward yields were not affected by phosphatic fertiliser treatments. The P status in silage was significantly reduced in the low P treatments in three out of the four years. This resulted in lower P levels in the slurry in the low P treatments. In the fourth year P status in the grazing swards was consistently reduced in the low P treatment. Milk yields and composition were not influenced by P treatment. There was some evidence that cow weight and body score of cows were adversely effected in the low P treatments towards the end of the trial. In the next phase of the work, phosphorus will be applied to all three treatments at similar rates, i.e. maintenance dressings of P will be applied to cows grazing on soils with Indices 1, 2 and 3, respectively. It is concluded at the end of this phase that there may be some scope for modifications to the index system as is currently recommended by Teagasc. It will be in 2001 before the extent of changes that can be made will be quantified and implemented.European Union Structural Funding (EAGGF