Tablelands fertiliser decisions for 2009
From the April 2009 edition of Agriculture Today.
This article is based on the situation facing producers in 2009.
Paddocks must be prioritised due to-cash flow limitations and high fertiliser-prices.
Some decisions, if implemented on a long-term basis, could cause the pasture system to move in the wrong direction.
To help prioritise paddocks and decide on fertiliser use in 2009, a first key action is to take a meaningful soil test to provide quality data.
Take a minimum 30 cores per sample which must be sampled to 10 centimetre soil depth, along a fixed transect, at the same time each year.
It is better to do a smaller number of representative paddocks per year than more on a random basis.
Use the Phosphorus Buffer Index (PBI) to determine the target Colwell Phosphorus (P) level and if the paddock is above target P, don’t fertilise.
If the paddock is at target P (for example, 20) use maintenance fertiliser rates – approximately 90 kilograms per hectare (Paddock Colwell P 18-22).
If below target P, you could use a maintenance fertiliser rate to hold, or if a long way below target, you could do nothing – the decisions here are controlled by stock numbers.
A scenario for doing nothing would be if a paddock is at Colwell P 12-14, and the target P for the paddock is 20.
How many stock will you run in 2009?
This question will determine how much country you need to fertilise.
Paddocks which are near target P level should be running stock at 10-15 dry sheep equivalent per hectare, no lower.
Local trial data has been 12-15 DSE/ha at a target P level of 20.
This decision of the correct stocking rate is made on our soil P level, not the fertiliser rate for the paddock.
As our soil P level drops our stocking rate will drop with it.
Local data, for soil with a PBI in the range 40 to 120, is:
- Four to five DSE/ha on country with no fertiliser history and with a Colwell P of 8.
- Approximately eight DSE/ha on pastures with a Colwell P of 14.
There is no point fertilising to grow more grass if you don’t use it.
If stock numbers are down, then the below target paddock mentioned above does not get fertilised.
Droughts dent our confidence on what we can carry, however don’t become too conservative.
Ground cover with a target of 70 per cent is your monitoring tool to assess if you are over stocked.
Soil depth and aspect – even in paddocks that are above or at the target P level, you should not fertilise parts of the paddock which have shallow soil depth on a harsh westerly aspect.
Forget about treating the whole paddock the same way and focus on the parts which will give you the best payback.
Other factors – the dollar payback from fertiliser decisions is also influenced by the profitability of enterprises.
The variation in profits from one livestock enterprise is greater than the difference between enterprises within a district.
At the lower profit end, the decision to use fertiliser might be questionable because of the lower capacity to generate profits.
In this situation, there are major issues about the enterprise which needs to be addressed with or before the fertiliser decisions.
Pastures respond to soluble P in the soil.
This will come from fertiliser applied and the cycling of nutrients within the soil.
Where you source your fertiliser P is another question.
The plant does not care.
You need to evaluate all products on a soluble P basis spread on the paddock and not on total P.
Some products provide additional benefits which you need to consider (for example insoluble P content, liming effect, other nutrients such as sulphur).
Contact Fiona Leech, district agronomist, or Phil Graham, livestock grazing systems technical specialist, Yass, (02) 6226 2199.
