Nutrient movement on your farm
Sarah Brown, DEPI Echuca
We often consider the movement of nutrients on and off farm but what about the movement of
nutrients within the farm boundaries? There is a redistribution of nutrients which occurs on farm, as
a result of cow movements and time spent within each area, and the feeding out of silage and hay.
We can get a better return from money spent on fertiliser by taking this into consideration.
A large portion of nutrients consumed by cows is excreted in manure and urine. For example,
between 70 to 80 percent of nitrogen consumed is excreted in manure and urine, while up to 66
percent of phosphorous and approximately 90 percent of potassium consumed are excreted in
manure.
The time cows spend in different areas of the farm influences the nutrient distribution. A larger
amount of nutrients are deposited in areas of the farm where cows spend a greater portion of their
time. The management of the cows and the location of water will also alter the distribution of
nutrients (e.g. around water troughs). Research has shown that the amount of time cows spend in
an area is directly proportional to the amount of manure and urine excreted. For example, if the
cows spend 20 percent of the time on the yards before being milked, 20 percent of the nutrient in
the cows manure and urine will be excreted in this area of the farm. In this case the nutrients will be
collected in the dairy effluent ponds and offers the opportunity to redistribute the nutrients over
the farm.
In most pasture based dairy systems, there is often an uneven distribution of nutrients across the
farm as a result of grazing management, fodder conservation and feed out. The paddocks closer to
the dairy are often grazed during the night, so cows are closer to the dairy for the morning milking.
The night grazing is often longer then the day grazing and therefore results in an increase in the
deposition of nutrients on these paddocks. Paddocks closer to the dairy are also utilised more
frequently than those further away also increasing the nutrient deposited. Paddocks where pasture
is cut and the hay and/or silage is not fed back out on the same paddock, but fed out on other
paddocks, become reduced of nutrients. Alternatively, if a large amount of feed is fed out in a
heavily stocked paddock (e.g. a sacrifice paddock), nutrients will build up.
Within a paddock there may also be an uneven distribution of nutrients as a result of cow
movement. Cows tend to spend a greater amount of time at the front of the paddock closer to the
gateway (waiting to get to the dairy shed and often where the water and hay source may be) and in
sheltered areas. This will also result in an increase in soil nutrients.
For farms located in the North east with hills and flats, nutrients are often migrated from the mid
slopes to the tops or bases of hills, this being where they tend to rest. This is compounded by the
fact that the pasture will be more palatable on the slopes when they return next rotation and will
often overgraze these areas and avoid the tainted pastures at the hill tops and bases.
You will need to be mindful of past paddock management when soil testing your farm. Your cow and
feed movement around the farm will have an impact on the nutrient levels across the farm. Soil tests
should be completed for different farm management zones. For example, the night paddocks and
day paddocks should each have a soil test, taken from an area representative of the farm zone. If
there are two or more soil types dominant within a management zone soil tests should be
completed for both soil types as they respond differently to nutrients applied.
To obtain a more uniform representation of soil nutrient status of an area soils samples should be
taken along the same transect each time so needs to be permanently marked at each end. This
reduces variation in soil test results compared to any other method of sampling and will allow more
accurate comparisons between years for tests taken from the same area. If there is evidence of
differing nutrient distribution within paddocks, through pasture growth and distribution of faeces
after grazing, you may wish to take a transect from a high nutrient area and another from a low
nutrient area to better support fertiliser decisions.
Being aware of the nutrient distribution on your farm can allow you to make better use of your
fertiliser which can save you money. To keep the fertiliser bill in check and minimise losses to the
environment without affecting pasture production you may choose to vary your fertiliser application
from a uniform application to lower applications of fertiliser on high nutrient areas and concentrate
on lower fertility areas as identified by your soil test.
Key points:
-
The time cows spend in different areas of the farm influences the nutrient distribution on
farm
There is often an uneven distribution of nutrients across the farm as a result of grazing
management, fodder conservation and feed out
Be mindful of past paddock management when soil testing your farm
Base fertiliser applications off your soil test to maximise efficiency in the use of fertilisers
and production