New Zealand Journal of
Agricultural Research abstracts
Modelling phosphorus losses
from pastoral farming systems in New
Zealand
R. W. McDowell
R. M. Monaghan
AgResearch Ltd
Invermay Agricultural Centre
Private Bag 50 034
Mosgiel, New Zealand
email: richard.mcdowell@agresearch.co.nz
D. Wheeler
AgResearch Ltd
Ruakura Research Centre
Private Bag
Hamilton, New Zealand
Abstract A
model was developed for incorporation
into the computer model “Overseer®
nutrient budgets 2” to
estimate phosphorus loss from pastoral farms to surface waters. The
model sums potential risk of phosphorus loss from soil (background)
with incidental losses attributed to the application of fertiliser or
effluent to fields or waterways. The overall risk is estimated as the
amount of P lost annually (kg P ha–1
yr–1).
Data
for 23 sites of grazed pasture (sheep, beef, and dairying) ranging from
small plot trials to catchments were used to validate each component of
the model. A good relationship (R2
= 0.97***)
was obtained between measured and estimated soil P losses for systems
without much incidental P loss. Similarly, a good relationship was
observed between measured and estimated overall (soil + incidental) P
losses for all systems (R2
= 0.96***).
The
estimated loss of P is categorised into low, medium, high or extreme
risk to the environment (<1, 1–2, 2–4, and >4,
respectively) and
best management strategies are suggested accordingly. The model shows
promise in directing responsible P management for New Zealand pastoral
farms. However, inadequacies are likely when scaling up the model for
use in large catchments where land use and soils vary greatly.
Keywords nutrient
budget; eutrophication;
incidental; background; transfer
A04006; Received 22 January
2004; accepted 26 July 2004; Online
publication date 21 March 2005
New Zealand Journal of
Agricultural Research, 2005, Vol. 48:
131–141
0028–8233/05/4801–0131 © The Royal Society of New Zealand 2005
PDF file of entire paper: Print-quality
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