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Soil phosphorus and runoff concentrations take a long time to
decline, once they build up from application of phosphorus fertiliser
and are sensitive to application of more.
NSW Department of Primary Industries (DPI) has found that on a soil
with optimal soil phosphorus levels, even though no fertiliser was
applied for four years, runoff concentration did not decline, according
to DPI soil scientist, Dr Warwick Dougherty.
"This highlights the importance of getting soil phosphorus management right," Dr Dougherty said.
"Within the constraints of dairying systems in most of NSW, farmers
can only influence some of the factors affecting phosphorus
concentration in runoff."
Research conducted over several years and recently completed at
Elizabeth Macarthur Agricultural Institute (EMAI), Camden highlighted
two factors that farmers can manage - the rate and timing of fertiliser
application.
"Within pasture systems, it is essential not to apply more than the
minimum amount of fertiliser required to maintain optimal production,"
Dr Dougherty said.
"Excessive rates of application can substantially increase runoff concentrations," he said.
The time lapse between fertiliser application and runoff occurring also has a major effect on runoff concentrations.
If runoff occurs within the week or so after fertiliser is applied, concentrations in runoff can be very high.
Avoiding application in high risk runoff periods is a useful
strategy for reducing runoff losses to waterways in regions with
distinctly seasonal rain.
Whenever possible, farmers should consider the possibility of rain
and subsequent runoff, although Dr Dougherty acknowledged that
predicting when both will occur is difficult in the environments in
which most NSW dairy farmers operate.
Research also revealed that three other key factors - the time
between grazing and a runoff event, pasture biomass, and phosphorus in
dung, influenced runoff.
"Further, the majority of the phosphorus in runoff from pastures is dissolved, not particulate," Dr Dougherty said.
"Hence traditional strategies to reduce phosphorus in runoff such as buffer or filter strips are unlikely to be effective."
The research was jointly funded by Dairy Australia and Land and Water Australia.
Editor's Note:
Original news release can be found here.
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