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Background
information
Standard soil fertility tests can provide a lot of information about your soils and differences between paddocks, no matter what your attitudes and preferences about using fertilisers. Soil nutrient deficiencies and imbalances can have a compounding impact — these soils are likely to have poor plant and root growth, low groundcover and litter levels and, therefore, a lower level of soil organic matter supporting fewer soil organisms such as bacteria, fungi and earthworms.
This procedure deals with the issues of taking a soil test, interpreting the results, and identifying soil health problems such as soil acidity or sodicity. Fertiliser decisions, which are essentially about pasture growth and maximising profit, are dealt with in procedure 7.1 in Grow More Pasture.
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Use soil tests to help monitor nutrient levels and soil health on different areas of your property
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Key decisions, critical actions and benchmarks
Even without a laboratory test, the number of earthworms present, and/or the ‘look, smell and feel’ test can give an indication about soil health. Tool 6.3 explains how to do these tests.
Take soil samples for testing
Tool 6.4 provides the directions for taking a soil sample for analysis at an accredited laboratory.
Standard soil tests provide an analysis of:
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Texture, colour, pH (usually in water and in calcium chloride (CaCI2)) and electrical conductivity (EC)
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Phosphorus (P), potassium (K) and sulphur (S)
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Calcium (Ca), magnesium (Mg), aluminium (Al) and sodium (Na)
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Calculations of cation exchange capacity, Ca/Mg ratio, Al saturation, Na percent of cations and the Phosphorus Buffer Index (PBI).
Sub-soils can also be sampled to monitor pH and aluminium. This is important to determine if sub-soil acidity will affect survival of sensitive species like lucerne or phalaris seedlings. For each soil type/paddock, take six soil samples from a depth of 30–40 cm.
Interpreting soil tests
Interpreting soil tests as part of developing a fertiliser strategy is discussed in tool 7.3 in Grow More Pasture which considers the use of phosphorus, potassium, sulphur and nitrogen.
Tool 6.5 is provided to help interpret soil tests for any soil health problems (acidity, sodicity, salinity and trace elements) on your farm.
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Read
Soil Analysis, an Interpretation Manual: edited by K.J. Peverill, L.A. Sparrow and D.J. Reuter (CSIRO Publishing: Collingwood).
Towards Sustainable Grazing – the Professional Producer’s Guide, Chapter 3, Soil Health and Nutrients: a collation of proven best practices for modern grazing enterprises in southern Australia. Order your copy from MLA by:
View
Making Better Fertiliser Decisions for Grazed Pastures in Australia: use the Farm Nutrient Loss Index tool (on CD) to create a farm map and assess the likelihood of fertiliser applications being lost from the site. Get your free copy of the booklet and software tool by:
Phosphorus for Beef and Sheep Farmers: detailed reports that help producers optimise phosphorus application and monitor soil phosphorus and farm fertiliser needs, which can improve on-farm profitability. Download reports for Tasmania, WA and SA at: http://www.wool.com/Publications.htm?cat=Pastures
Soil Acidity: a wide range of fact sheets covering soil health issues (not just acid soils). Visit the NSW DPI website: http://www.dpi.nsw.gov.au/agriculture/resources/soils/acidity
Identifying Gypsum-Responsive Soils: describes the action and benefits of gypsum in dispersive (erodible) clay soils. Visit the DAFWA website: http://www.agric.wa.gov.au/content/lwe/land/cult/fn057_1990.htm
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