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The evaluation of environmental, agronomic and economic implications of high and low input dairy systems.
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1999-11-01
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Culleton, N., Murphy, J., Murphy, W.E., The evaluation of environmental, agronomic and economic implications of high and low input dairy systems, End of Project Reports, Teagasc, 1999.
Abstract
This 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.