Building and maintaining soil fertility
High performing, improved pasture species require
good soil nutrition. Nutrients are removed from the
system over time. See table on right, which shows
typical nutrient removal rates for a range of products.
Nutrient response curves are used to determine the
expected production response to fertiliser applications.
They allow farmers to assess whether they have
adequate soil nutrient levels to reach their pasture
production targets.
For example, consider an extensive sheep/beef
enterprise with a Phosphorus Buffering Index of 130
and a current Colwell P of 17 mg/kg. To achieve 95%
of potential pasture production would require an
increase in the phosphorus status of the soil to around
36 mg/kg. See graph below.
Knowing where each paddock’s soil phosphorus level
sits in relation to these critical values gives graziers
the power to better manage soil fertility, fertiliser
applications, pasture productivity and stocking rates
according to their risk profile.
Your adviser can use this information to determine
appropriate maintenance and capital fertiliser
applications to meet your targeted stocking rates.
To explore these response curves further, take a look at
the handy calculation tool on the Meat and Livestock
Australia website called ‘Five easy steps to ensure you
are making money from superphosphate’.
Typical nutrient removal rates (kg of nutrient/t or kL of product)
Product (1 t or kL)
N
P
K
S
Ca
Mg
Mixed pasture/hay
18
1.8
15
1.6
5
1.8
Lucerne hay
28
2
24
2.6
9.9
2.7
Cattle (live ex farm gate)
26
7.2
2
1.4
12
0.4
Sheep (live shorn ex farm gate)
23
5.9
2.1
1.4
11
0.4
Merino, greasy fleece
119
0.3
15
22
1.8
0.59
Milk (cow)
5.3
0.93
1.6
0.3
1.2
0.10
Source: National Land and Water Resources Audit Project, Nutrient Balance in Regional Farming
Systems and Soil Nutrient Status, Appendix 6, September 2001.
Potential carrying capacity
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Carrying capacity (DSE/ha)
As well as addressing any nutrient deficiencies, graziers
may need to apply phosphorus and sulphur fertilisers
every year to sustain high levels of production.
95% of max.
20
15
10
Your
current
position
5
Colwell P
0
0
10
20
30
40
50
60
70
Soil P fertility level (mg P/kg soil)
Graziers can use the new Five Easy Steps tool to create a soil fertility and carrying capacity
relationship which reflects their farming conditions to see the potential for improvement
on their farm. This tool is intended to assist farmers in determining suitable levels of
phosphorus fertilisation of temperate pastures grazed by sheep and beef cattle on acid
soils in southern Australia. Source: Five Easy Steps to ensure you are making money from
superphosphate, CSIRO and Industry and Investment NSW, 2011.
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