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The Agricultural Liming Industry And Liming Technology

M. Conyers

Department of Agriculture, NSW Agricultural Research Institute Wagga Wagga. NSW 2650

Liming materials are derived from deposits of the rock, limestone (CaCO3). Most of our deposits of limestone are of organic origin. The calcareous skeletons of marine organisms (coral and shells) are changed into rock by high temperatures and pressures during tectonic upheavals. The south-eastern Australian limestones are generally of Silurian and Devonian age, which is old even on the geological time scale. Their great age has allowed the development of numerous limestone cave systems, most of which are along the western edge of the Great Divide. Perhaps there were once coral reefs along the west of the present mountain range during some inter glacials when there was an inland sea?

Limestone is mined from open cut quarries and undergoes a series of crushing and screening steps until the desired fineness for the end product is achieved. For ameliorating soil acidity the limestone has to be crushed to a size which has a powdery feeling. Under NSW legislation the minimum standard for registration is that 80% of the liming material must pass through a 0.71 mm aperture screen. The percentage passing 0.25 mm must be stated on the label. (If this information is not given, or the material is not even registered, purchase of the material may be ill-advised). In short, agricultural limestone is simply a “biological rock” which is being “recycled” by crushing to a powder.

Alternative materials for liming which are presently sold in this region are the precipitator dusts which are by-products from cement manufacture. These materials may contain varying amounts of CaO (burnt or quick lime) and impurities. They are also subject to the same legislative controls on fineness and purity as the crushed limestones.

The geographical distribution of acid soils is predominantly to the east of the line shown in Figure 3.1. Also shown in Figure 3.1 is the location of commercial limestone deposits and outlets, limestone caves and the two sources of precipitator dust which sell into the Riverina. Two sources of dolomite, at Mt Gambier and Mudgee, are not shown on the map. These tend to be expensive for either production or transport reasons. Also not shown on the map are two potentially commercial sources of limestone which are nearer to our district than the present ones, but neither is within 140 km (road) of Wagga. For the NSW deposit and plant to be opened, it must be approved by the Local Councils involved, the State Departments of Local Governments, Lands, Mineral Resources, Environment and Planning, and the State Pollution Control Commission. The limestone company then has to put in roads, power lines and water before the plant can be built. All this to capture a market which runs from January to May and fluctuates heavily year to year. The capital outlay in developing a new deposit would be huge and associated with a high risk in year one sales. The lime produced would therefore not be cheap. A good example is the attempted reopening of the Tumut deposit in 1984-85, where the ex-works price for a sandy feeling liming material Wd5 barely less than the landed price of Superfine F70 from Moss Vale.

Figure 3.1 Limestone deposits, limestone caves and sources of liming materials.
l Comercial deposits &/or plants
t Limestone Caves
n Precipitator dust sources

Table 3.1 The typical per tonne cost of liming a paddock at Wagga, NSW.


Ex Works

















At an application rate of 2.5 tonne/ha (1 ton/acre) = $150-180/ha

This leaves Wagga in a limestone deposit void. The cost structure of the industry is therefore critical to our collective understanding and decision making.

In this part of the world the profit made by the lime companies for agricultural products is small. Industrial markets for crushed limestone are more attractive both in terms of potential profit margins and consistency of demand.

Transport costs have been relatively steady and in some cases even declined in 1985. The competitiveness of the trucking industry has left them small profit margins. The flow on in reduced fuel prices in early 1986 assisted keeping transport prices low even though the potential for fuel savings was stifled at Federal level. Some trucking companies have now geared up for the liming industry by obtaining regular backloading business out the region, again contributing to steady transport prices.

Spreading contractors generally do not make a big margin either. The machinery required for lime spreading is specialised and the work is only seasonal at present. The potential exists to lime pastures in the winter off-season and to then mix the lime into the soil in preparing for the cropping cycle.

The reseller or agent makes a margin which is sometimes difficult to isolate. Some organise the transport of lime and may even use their own trucks; some organise the spreading contractor for you or provide their own operator and machine; some hire out machines; some do several of the above while others just relay the order from the farmer to the lime company and pick up a margin for carrying the account. In the past, there have been many resellers who have collected significant per tonne margins simply for a phone call and an invoice. That is no longer possible. There are now several companies feeding into the Riverina and each may have several outlets. Major suppliers include David Mitchell Estate (Lilydale, Vic), Southern Limestone (Moss Vale), OMYA Minerals (Bathurst), Slag Lime (Marulan) and the two precipitator dusts from Geelong and from Marulan. With such competition no one can afford to offer inflated prices. However, despite this competition, there will be no price miracles for the Riverina for the reasons I have outlined above. To overcome our acidity problem we will need a combination of lime company competition, acid-tolerant cultivars and sound liming technology (application rates, incorporation methods, etc).

The social cost of continued soil acidification and the relative unattractiveness of our market for lime company expansion means that there is a good case for government intervention by subsidisation; that is, if the paperwork were tolerable, and if we could sell our wheat.

To finish on the bright side, once you apply limestone to an acid soil, the life expectancy of 2-3 tonne/ha in this region (450-600 mm rainfall annually) is easily 10 years before you end up where you started. On some trials of Brendan Scott (the second speaker) there is not even measurable evidence of decline in pH, 5 years after the limestone was applied. It appears that the major hurdle we face is that awesome initial cost, and less than 40% of that cost is the lime itself.

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