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Background
information
Building up and maintaining soil fertility is one of the most cost-effective investments than can be made in a grazing enterprise. Not only are many Australian soils inherently low in nutrients, these nutrients are constantly removed in animal products (meat and wool) as well as in hay, silage or crops.
Laboratory soil tests, plant tissue tests and the use of fertiliser test strips can all assist in making sure that the right amount of the correct fertiliser is being applied to meet your pasture growth objectives.
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Develop a soil testing program for your property to determine if nutrients are limiting pasture growth
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Use the tools in this module to determine appropriate capital and maintenance fertiliser rates to address soil nutrient deficiencies.
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Introduction
The decisions relating to fertiliser application (such as the type that most suits your operation and the rates you might use) are essentially about pasture growth and maximising profit, and are dealt with in this module.
Tool 6.4 in Healthy Soils contains instructions for collecting soil samples for laboratory testing. Identifying soil health problems, and assessing the need for remedial action or special management are addressed in procedures 6.3 and 6.4 in Healthy Soils.
Poor soil nutrient availability contributes to low pasture growth, low levels of desirable grasses and legumes and poor feed quality across most of the high-rainfall and wheat–sheep zones of Australia.
Key decisions, critical actions and benchmarks
Without gathering some objective information, it is very hard to assess the nutrient levels of the different soil types or management units on your property. There are three ways to get this information:
- A laboratory soil test will identify if the macro elements (phosphorus, P; potassium, K and sulphur, S), are limiting pasture growth. Standard laboratory soil tests are not useful for assessing N or trace element requirements. Tool 6.4 in Healthy Soils outlines the correct procedure for collecting soil for a laboratory test. Soil tests also give you information about soil health (acidity, salinity, sodicity, etc and whether your soil might be responsive to lime, gypsum or added nutrients). These issues are dealt with in procedure 6.3 in Healthy Soils. Use tool 7.3 to help interpret soil tests
- Plant tissue tests are more effective than soil tests if trace elements are limiting pasture growth. Trace elements include molybdenum, copper, zinc and boron. Experienced local farmers, agronomists or veterinarians will know if trace element deficiencies are likely in your district. If you wish to assess the trace element requirements for pasture growth, take a sample of the most dominant clover in the paddock during spring and submit samples to a reputable laboratory (see signposts). You will need to contact the laboratory to get the correct sampling technique for the trace element you are testing for.
- Do it yourself, using fertiliser test strips. You can directly assess the likely response from fertiliser applications by laying out test strips in your paddock(s). Test strips can be used for any fertiliser type and are particularly suited to situations where there is not a satisfactory laboratory test (eg, for N, trace elements or gypsum), where deficiency symptoms are not highly characteristic, or where you want to test non-traditional fertilisers. Use tool 7.2 to set up and monitor your own fertiliser test strip.
Figure 7.2. The effect of fertiliser on average monthly growth rates at Hamilton, Western Victoria (winter rainfall area) and Orange, Central Tablelands NSW (uniform rainfall area). Hamilton data simulated from GrassGro; Orange data from NSW PROGRAZE®.
Understanding pasture responses to nutrients
Two examples of how much extra pasture can be grown, when nutrient deficiencies are corrected, are shown in figure 7.2 for an introduced pasture at Hamilton (Vic) and a native pasture at Orange (NSW).
Phosphorus and native pastures
Native pastures containing some legume (eg, sub clover, cluster clover, medics) will respond to low rates of phosphorus (P) fertiliser. However, native species can decline under competition from clover, annual grasses or broadleaf weeds if fertility levels are raised and the additional feed not utilised. For native pastures, about 20% legume content in spring is the recommended maximum level.
For native grass pastures in high conservation areas or where an increase in native species diversity is desired, do not apply fertiliser or legume seed as both will reduce the conservation value.
Phosphorus and introduced pastures
Introduced (also called exotic or improved) pasture species have a higher requirement for nutrients than native grasses so fertilising paddocks with these species will give a bigger response.
Generally, it is the legume component of the pasture which gives the immediate production and feed quality response to P fertilisers such as superphosphate if there are no other limiting factors such as acid soil. The legumes fix N, which becomes available to the grasses when the legume roots die off.
Nitrogen fertiliser
We usually rely on legumes to supply N to the grasses in the pasture, but applying N fertiliser to supply additional N is economical in some situations. Review the guidelines for the use of N in tool 7.4 to assess whether N fertiliser will be profitable for your sheep enterprise.
Protect the environment
Ensure the proposed nutrients do not adversely impact on the environment. Given the prevailing conditions in a paddock, eg, proximity to drainage lines, amount of bare ground, etc, nutrients may be easily lost to erosion or leaching beyond the root zone. Use tool 7.4 to quickly assess any potential nutrient losses.
Economics of fertilising pastures
The economic benefit of correcting nutrient deficiencies was evaluated by more than 100 producers (in Vic, NSW, Tas and SA) who participated in the Grasslands Productivity Program (GPP) from 1993 to 1997 (table 7.1). Pasture types ranged from improved perennial to annual to native. The average return was $1.89 for every dollar spent on fertiliser and livestock.
Table 7.1 The economic benefit of correcting nutrient deficiencies, for producers who participated in the Grassland Productivity Project (GPP) from 1993 – 1997. Source: Grassland’s Productivity Program - final report to members (1998) prepared by J. Court. The Grasslands Society of Southern Australia.
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GPP (Vic, NSW, SA, Tas)
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Victorian GPP sites
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NSW GPP sites |
Change in Stocking Rate
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Data unavailable
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+28% |
+34% |
Change in Gross Margin
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+25% |
+25% |
+30% |
| $ Return per $ Spent |
$1.89 |
$2.17 |
$2.28 |
Signposts  |
Read
The MLA Pasture Health Kit: a field kit for producers to assess pasture health in the paddock. The kit can be ordered from MLA by:
Making Better Fertiliser Decisions for Grazed Pastures in Australia: provides soil test – pasture response relationships and interpretations for the major soil tests P, K and S used in Australia, and the Farm Nutrient Loss Index tool (on CD). Get your free copy of the booklet and software tool by:
Five Easy Steps to ensure you are making money from super phosphate tool: combines years of research, data and information and leads readers through a decision making process for investment in P. The tool was developed by CSIRO and Industry & Investment NSW with funding from AWI and Pastures Australia members. Available to download at: https://www.mla.com.au/extension-training-and-tools/tools-calculators/phosphorus-tool/. For background information download the Five easy steps: P tool user booklet.
Soil Analysis, an interpretation manual (1999). Edited by K.J. Peverill, L.A. Sparrow and D.J. Reuter (CSIRO Publishing: Collingwood). Go to http://www.publish.csiro.au and use the search function.
Plant Analysis, an interpretation
manual (1997) Second Edition, edited
by D.Reuter and J.B Robinson (CSIRO
Publishing). Go to http://www.publish.csiro.au and use the search function.
Running a sustainable grazing business. This section of the MLA website provides a variety of resources based on the well known (but out of print) publication Towards sustainable grazing - the professional producer's guide. Go to: www.mla.com.au/research-and-development/environment-sustainability/sustainable-grazing-a-producer-resource
Grazing Best Management Practices website. The Grazing BMP program is a voluntary, industry led process which helps graziers to identify improved practices which can assist the long term profitability of their enterprise. It also helps identify the steps you need to take to incorporate best management practices into your enterprise. Go to: www.grazingbestprac.com.au/index.html
MLA’s More Beef from Pastures – the producer’s manual: the Pasture Growth module, one of eight modules and practical tools to build a more profitable beef business. View online at: https://www.mla.com.au/extension-training-and-tools/more-beef-from-pastures/
View
The Australasian Soil and Plant Analysis Council (ASPAC) website: provides a list of soil and plant testing laboratories that are part of the ASPAC testing proficiency program. Visit: www.aspac-australasia.com
Trace elements for pastures and animals in Victoria: includes background information on molybdenum, boron, zinc, copper, cobalt and selenium requirements. Visit: http://vro.agriculture.vic.gov.au/dpi/vro/vrosite.nsf/pages/trace_elements_pastures
Micro-nutrients (trace elements) for high rainfall pastures: WA Agriculture and Food website. Visit: www.agric.wa.gov.au/high-rainfall-pastures/micronutrients-trace-elements-high-rainfall-pastures
Grazclock: a spreadsheet-based tool that matches animal feed requirements with pasture growth throughout the year. It allows sheep (and cattle) producers to select key management times to correspond with feed demand. Contact NSW I & I by emailing: douglas.alcock@industry.nsw.gov.au
Web-based sources of technical information on soils, fertilisers, pasture species and growth rates, for each state can be found by searching the following state agency websites:
Attend
Paired Paddock Program (PPP)™, formerly called Grasslands Productivity Program: a farm-based course for sheep producers who want to look at the economics of improving soil fertility and the potential carrying capacity of paddocks on their farm. PPP is delivered by:
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