Australian agricultural limestone: What’s eating Australia?

By Paul Rackstraw
Published: Monday, 26 September 2016

With soil acidification eating at Australia’s multibillion dollar agricultural market, Richard Flook, Consultant, and Cameron Perks, IM Australian Correspondent,* take a look at what is being done to help farmers improve their productivity and the growth required in the Australian agricultural limestone industry.

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Australia is a large producer of agricultural commodities and ideally situated to supply the expanding food markets in Asia, particularly those arising from the expanding middle classes of China, India and the ASEAN region.

Despite a large land area, agricultural production can be limited by variable rainfall but mainly by the soil quality.

Past farming practices, including inefficient use of fertilisers combined with land clearing and sometimes an inherent fragile soil horizon, have resulted in large areas of acid soils and provided the need for large scale and a growing application of agricultural limestone.

Australian agriculture

Australian agriculture earned Australian dollar (A) $150bn ($114bn**) and made up 11% of Australia’s Gross Domestic Product (GDP) in 2014.  About two thirds of Australian agricultural production is exported mainly to China (20%), Korea and Japan (16%) and ASEAN (14%).

The grain-producing agricultural zone of Western Australia is located in the south-west of Australia. In New South Wales the grain production areas are located in the slopes and plains regions to the west of the Great Dividing Range and on the northern coastal floodplains to the east of the Great Dividing Range. Victoria’s grain farms are predominantly located in western and northern Victoria, with the majority in the Mallee and Wimmera regions. 

In South Australia grain cropping is mainly north and east of Adelaide and on the Eyre Peninsula.  The South East region of South Australia was traditionally regarded as a grazing area but cropping is increasing in this area.  

The grain producing agricultural zone of Queensland is located largely in the south of the state and within 400 km of the coast. However, Queensland crop production by value is predominantly sugarcane followed by cotton, wheat and bananas.

Figure 1 Australian wheat planted area ('000 Ha) 
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Source: Department of Agriculture & Water Resources 


Figure 2 Australian wheat production ('000 tonnes) 
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Source: Department of Agriculture & Water Resources 


Figure 3 Australian canola planted area ('000 Ha) 
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Source: Australian Oilseeds Federation 


Figure 4 Australian canola production ('000 tonnes) 
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Source: Australian Oilseeds Federation 


Wheat

About 60% (12.7m hectares (Ha)) of Australian cropping area is used for wheat production and although Australia only accounts for about 3% of world production, the majority (70%) is exported and Australia holds about 10-15% of the global wheat trade. Similarly, about 70% of barley produced, which accounts for 20% (4.1m Ha) of cropping area, is exported.

The wheat cropping area in Australia has been relatively constant in recent years (Figure 1) although production has varied significantly due to seasonal climate and rainfall (Figure 2). Cropping area rather than production is the prime indicator of fertiliser or agricultural limestone demand.

Canola

Canola is the major oilseed crop in Australia which account for about 11% (2.5m Ha) of total Australian cropping area. Canola plantings commenced in 1993 and grew rapidly due to two decades of successful breeding research (Figures 3 and 4). About 75% of production is exported making up 15-20% of the global export trade.

Sugar

Around 95% of sugar produced in Australia is grown in Queensland and about 5% in northern New South Wales. About 75% of sugar production is exported.

Sugarcane is a vigorous tropical grass and has very high nutrient requirements to produce commercial crops. The majority of cane growing soils are poor, and this combined with the high nutrient removal rates of the crop, mean that a full suite of nutrients must be applied every year to ensure high productivity.

Soil pH for optimum sugar cane production is between 5.5 and 7.5 and addition of agricultural limestone can be used to correct for acidification caused by application of ammonia or urea-based nitrogen and phosphorus fertilisers. Replacement of calcium (Ca) and magnesium (Mg) taken up by the sugarcane is also required and dolomite or limestone/magnesite blends are used to provide the required magnesium.

Figure 5 Surface soil acidity profiles 
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Source: Soil Quality 


Australia’s current soil situation

Only 6% of the total soil in Australia is considered arable. 

In 2015, the Australian government established a set of national science and research priorities with corresponding practical research challenges. Soil and water was one of nine priorities and one of the largest recipients of government funding.

The impact of European farming practices on Australian land and soil degradation was particularly severe from settlement up until the 1950s. Erosion control procedures became more prevalent after that period and farming practices and soil management have steadily become more sophisticated and effective. However significant problems still exist; soil erosion is still a problem in some parts of Australia where erosion rates are 1,000 times the rate of soil formation; northern Australia is deficient in nutrients while the southern region has excess; soil compaction is widespread and soil organic stocks are low. 

Finally, soil acidification in a number of cropping regions is a major factor restricting soil use and crop yields.

Figure 6 Western Australian agricultural limestone sales 
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Source: Chris Gazey (DAFWA) & Lime WA 


Figure 7 Victoria agricultural limestone sales 
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Source: Victoria Department of State Development, Business and Innovation 


Figure 8 New South Wales agricultural limestone sales 
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Source: NSW Department of Industry 


Acid soils

Soil acidification is a problem marked by a threshold which if passed becomes a problem where the cost of repair far exceeds the cost of prevention. This threshold or critical value is a soil pH of about five. About 50% of Australian agricultural land or 50m Ha have surface pH values less than this critical value. 

Soil pH in calcium chloride (pH (CaCl2) pHCa or pHCa) is the standard method of measuring soil acidity.  This test is considered to better reflect what the plant experiences in the soil and be more accurate than soil pH in water expressed as pH (w). Roughly pH (CaCl2) values are about 0.7-1.0 pH units below pH (w) values.

The extent of the problem can also be illustrated by the respective regional soil pH profiles (Figure 6). About 75% of surface (0-10cm) soil sample are below pH (CaCl2) 5.5 in Western Australia with about 70% in New South Wales and about 30% in Victoria. In both Western Australia and New South Wales about 30% of surface soils tested are below pH (CaCl2) 4.8, with 45% of 10-20cm and 20-30cm samples in Western Australia below pH (CaCl2) 4.8. 

There is now growing evidence that traditional agricultural limestone application of about one tonne per hectare every ten years is not sufficient particularly for sub-surface soils.

It is estimated 14.25m hectares of WA’s wheat belt soils are already acidic or at risk of becoming acidic. This erodes potential crop yields by about 9 to 12% at a cost of almost A$500m annually. Grain growers are being encouraged to increase application rates from 1-1.5 tonnes /Ha to over 2 tonnes/Ha and to increase testing of acidity in sub-surface soils.

In New South Wales it is estimated that over half of intensively used agricultural land is affected by soil acidity and lost production exceeds $400m annually. Canola farmers were reported to be using 2.5 tonnes of limestone/Ha before initial crops and 1.8 tonnes/Ha after twelve years.

Recent trials in south-west Victoria have indicated that subsurface acidity is a bigger problem than previously thought and that surface application of limestone can take more than three years to increase pH below 10cm if at all.

More than 2.5m Ha are at risk of soil acidification in South Australia with 60% of agricultural land in the Adelaide-Mt Lofty region in South Australia susceptible to soil acidity. Soil pH monitoring and investigation programs through from 2007 to 2012 indicated that in acid prone areas, 40% of topsoils and 48% of subsurface layers (10–20 cm) were below a critical level of pH(CaCl2 ) 5. Subsurface acidity is an established problem that is more difficult to treat. As an example, an estimate of the annual limestone requirement for one part of the region is 28,000 tpa, an increase of 50% from the current rate of about 18,000 tpa.

Acid Sulphate Soils 

Acid Sulphate Soils (ASS) are soils or sediments containing highly acidic soil horizons or layers resulting from the aeration of soils or sediments that are rich in iron sulphides, commonly pyrite. This aeration (oxidation) produces acid (particularly hydrogen and aluminium ions) in excess of the soils or sediments capacity to neutralise the acidity, resulting in soils or sediments with pH (CaCl2) 4 or less.

ASS occur naturally over extensive low-lying areas of Australia’s eastern coastal floodplains and particularly in coastal Queensland and New South Wales. If disturbed, ASS can release large quantities of leachate containing acid and metal contaminants into the environment. 

Soils are divided into two categories: AASS-Actual Acid Sulphate Soils and PASS-Potential Acid Sulphate Soils. Queensland State Planning Policy 1/00 Planning and management of coastal development involving acid sulphate soils is a key document, particularly Annex 3 which specifies the tonnages of agricultural limestone required.

Traditional limestone spreading techniques are not adequate for ASS/PASS and soil recycling is more effective in order to add the very high levels required (reported up to 270 Kg agricultural limestone per tonne of ASS or PASS).

Australian limestone geology 

Limestone is a very common and often impure sedimentary rock consisting of 90% or more of calcite (CaCO3), with the 10% being a mixture of dolomite (CaCO3.MgCO3) and various impurities, such as silica. 

Marble could also be considered 'limestone’, even though it has been recrystallised through metamorphism. In many applications, marble and limestone are interchangeable.

The most common source of calcium carbonate in the world is limestone itself, but in some places other calcareous sediments or other calcareous materials, such as coral, are used.

Western Australia

High quality CaCO3 is available from lime sand, limestone and dolomite sources;  with limesand being the most dominant source. Limestone for agriculture is mined and crushed from the state’s coastal Tamala limestone deposits. This limestone is 1–2 million years old and was formed by cementation of limesand deposits.

South Australia

Marble formed by the metamorphism of limestone is an important source of calcium carbonate in South Australia, as is shellgrit, an unconsolidated accumulation of sea shell debris found in beach ridge deposits along the coastline. 

Tertiary aged limestone is mined for agricultural uses by Sibelco Ltd at their Caroline deposit, 25km southeast of Mount Gambier. Extensive tertiary aged deposits occur in South Australia on the Yorke Peninsula, in the Gambier Embayment of the Otway Basin, the Murray Basin, and in the Eucla Basin. 

Victoria

Limestone in Victoria varies in age from Palaeozoic to Quaternary, with younger limestones often being friable and porous, and older limestones being dolomitised and silicified, or metamorphosed and recrystallised to marble.  

According to the Geological Survey of Victoria (GSV), the state’s Palaeozoic limestones and dolomites are higher grade deposits which formed in marine settings (typically >95% CaCO3), whereas tertiary limestones were formed in a range of subaqueous and subaerial environments (typically 75-95% CaCO3).  

In addition, Victoria is host to Cambrian aged limestones which are yet to be exploited.

Limestone deposits suitable for agricultural use are widespread in the state. Limestones of tertiary age occurring in the southern part of the state (from South Australian border to East Gippsland) have historically been the main source of agricultural lime.

New South Wales

New South Wales (NSW) has abundant resources of limestone. Researchers and companies have taken particular interest in NSW due to its high purity deposits. 

There are over 400 limestone deposits known in NSW scattered across the state. Despite this, most of them remain undeveloped due to the local competitiveness and size of the local market. According to work carried out by the NSW Government’s Geological Survey, the areas with greatest potential for high purity limestone occur south of Yass, northeast of Cooma, near Bathurst, north of Tamworth, around Ashford and from Molong to Canowindra.

Most limestones in those aforementioned areas are biogenic in nature, and tend to form long, comparatively narrow bodies with abrupt margins.

Queensland

Queensland is host to a large suite of regions prospective for economical limestone resources. The Chillagoe Formation, Broken River Province, New England Origin, and Burdekin Basin are all known to contain significant limestone resources.

Agricultural limestone production and producers

Published agricultural limestone application in grain growing areas of Western Australia is approximately 1.6m tonnes pa and has grown rapidly particularly due to increasing canola production (Figure 6). Total agricultural limestone application in Western Australia is estimated to be closer to 1.75m tonnes.

Recent South Australian agricultural limestone production figures are not available. Between 1998 and 2008 average application was 110,000 tpa.  The current application rate is estimated to be still at this level.

Current Victorian agricultural limestone application is estimated to be 500,000 tpa, although much higher levels have been recorded in previous years and the 10 year (2004/05-2013/14) average application rate was about 550,000 tpa (Figure 7). 

The published New South Wales agricultural limestone application rate is currently about 300,000 tpa (Figure 8). However the actual application rate averaged 450,000 tpa in the 10 years to 2006/07 and is estimated to be currently much higher at about 600,000 tpa.

Agricultural limestones application rates in Queensland and Tasmania have been estimated at approximately 300,000 tpa and 110,000 tpa respectively.

Total Australian production

The total agricultural limestone application in Australia will vary annually but is estimated to be currently about 3.4m tonnes and,  based on estimated purity levels, this is equivalent to about 2.9m tonnes at 100% CaCO3 (Table 1 and Figure 9).

Major Australian producers of agricultural limestone are listed in Table 3.

Table 1 Estimated Australian agricultural limestone application 
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Source: R Flook estimates 

Figure 9 Australian agricultural limestone
application (2.9m tonnes @ 100% CaCO3 tonnes) 
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Source: R Flook estimates 

Figure 10 Effect of limestone particle size on soil pH 
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Source: North Carolina State University 2003 

Table 2 Agricultural Limestone Physical Effectiveness scales 
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Source: Grains Research & Development Corporation (Project Code SFS 00026) 


Product Specifications

Purity and sizing of the agricultural limestone are the key factors influencing liming efficiency. Available neutralising value and calcium level are important and some magnesium is beneficial in the agricultural limestone. Smaller agricultural limestone particles will react more quickly than larger particles which may provide pH control (buffering capacity) over a longer period of time. The biggest pH change will occur within 3-4 months and the pH may continue to increase for 6-12 months (Figure 10).  

Producers of agricultural limestone in Australia commonly publish calcium carbonate analysis and neutralising value (N.V.) which is the acid neutralising ability compared to 100% CaCO3. 

However, N.V. can also vary by size fraction and the more sophisticated producers take this into account by expressing an Effective Neutralising Value (E.N.V.). E.N.V. takes into account both the acid neutralising ability and the liming physical effectiveness of the different size fractions preferably based on actual field trials.  

Trials in New South Wales have shown that the minus 75 micron fraction is most effective and this rapidly decreases to less than half the physical effectiveness at 250 microns. 

On the other hand, many producers in Western Australia use a scale that gives equal maximum effectiveness for all particles less than 500 microns. In South Australia and Victoria, particles below 300 microns are given equal maximum effectiveness. 

Some other producers in other regions of southern Australia do not publicly acknowledge the effect of particle size at all. A national physical effectiveness (PE) scale and mandatory reporting of particle sizes and E.N.V. would obviously be preferable to the current situation. The New South Wales scales which are based on field trials with commercially available limestone products have been recommended (Table 2).

A further refinement in the E.N.V. calculation incorporates an allowance for particle surface area due to limestone morphology and enables the farmers to have an even more practical comparison of competitive sources in the first 12 months after application.

Market - developments and outlook

Correct soil pH is important for the health of a variety of crops, with barley, canola, faba beans and lucerne being most sensitive to soil acidity, and wheat, peas and phalaris not being far behind.

A recent survey in central-west New South Wales has shown that between 2000 and 2015 soil pH has declined even further in the majority of locations. An estimated A$1bn is lost in crop production each year due to acid soils in Western Australia and NSW alone, and agronomists agree that more needs to be done.

Lisa Miller, research and extension officer at Southern Farming Systems Victoria suggests that while application of limestone is on the increase, further increases are required. 

"We’ve been concentrating a lot on the top soil (top 10cm), however there has been acidification occurring from 10-20cm in Victoria in particular. How we get limestone down there is a bit of a concern because we’ve been surface supplying it, which doesn’t seem to get down to where it’s needed," Miller told IM

Dr Guangdi Li, principal research scientist at the NSW Department of Primary Industries, said that "for those areas that soil is acidic to depth, probably deep ripping with limestone is a good option" adding that "limestone should be incorporated into soil for the better results. It is better put into the ground during the crop phase in mixed farming areas."

Both Miller and Li agree that not enough limestone is being applied in general, but that the right amount of limestone for deep acidification is currently unknown, with laboratory and glasshouse experiments now underway to give better insight within the next few years.

One solution put forward by the Western Australia’s State Limestone Strategy was a network of regional quarries in the South West approximately 50km apart to supply limestone into the agricultural areas. However, serious doubts have been raised as to whether there are enough undeveloped deposits. The solution may be simply to increase output from existing quarries. 

Extra quarries are also needed in Victoria according to Miller, who said that "some pits have virtually run out of agricultural limestone", adding that she is concerned that producers will struggle to keep up with demand.

Cameron Weeks, Regional Cropping Solutions Networks facilitator, added that many cropping paddocks in Western Australia’s northern wheat belt now had good phosphorus (P) levels, so P investments could also start to be diverted to limestone.

He estimated growers could save about $15 per hectare per year by not applying standard P rates on paddocks that had sufficient levels.

Miller adds that the grazing industry is "very much lagging behind the cropping industry in terms of limestone application" and that "we are moving towards a crunch time where a lot of grazing farms will struggle to maintain production levels".

Omya Australia have introduced 2-6 mm Calciprill® a fine ground (< 100 micron) limestone which is pelletised with molasses. The pellets can be direct drilled or air seeded or sown or spread with fertilisers and seeds. 

Initially marketed into high value applications such as aerial spreading, golf courses and turf farms, the product is being tested in pasture applications. 

Some initial tests have shown that pellets drilled with phalaris seed at an effective rate of 150Kg/Ha was equally as effective as three tonnes per hectare of broadcast agricultural limestone. 

However, the benefits may have come from the micro-environment around the seed rather than broad acid soil remediation.

Outlook

Chris Gazey, senior research officer at the Department of Agriculture and Food Western Australia (DAFWA) has estimated that 2.5m tpa agricultural limestone (up from the current level of 1.6m tpa) would be needed over the next ten years to recover acidic soils in Western Australia alone.

The increasing need for agricultural limestone as well as the rise of limestone quarry production throughout Western Australia and inevitably the rest of southern Australia implies that the Australian agricultural limestone industry could potentially grow by 50% or an additional 1.7m tpa (1.5m tonnes at 100% CaCO3) in the near future. 

The potential cost benefits are also compelling. Assuming an average cost of spread agricultural limestone of A$55/tonne the additional cost of about A$100m pa represents less than 10% of the potential benefit of over A$1bn pa from improved crop production.

Table 3 Australian agricultural limestone producers 
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Note: Neutralising Value (N.V.) of 100% CaCO3 is 100
Source: Company reports, Lime WA, Limestone Association of Australia, Victorian Limestone Producers Association 

**Conversions made September 2016


*About the authors

Dr Richard Flook has worked for both suppliers and consumers of minerals with global companies including Steetley plc, Anglo American, Commercial Minerals (now Sibelco), Normandy Mining Ltd, Omya AG and Shinagawa Refractories.

Richard has been CEO, Managing Director & Director of Asian and Australasian companies. He has specialised in new business opportunities including strategic planning, trading, market development and acquisitions in the industrial minerals industry and has been involved in managing and developing mineral operations and businesses in Asia and Australasia.

Richard is a Fellow of the Australasian Institute of Mining & Metallurgy (FAusIMM (CP)), the Australian Institute of Company Directors (FAICD) and the Australian Institute of Energy (FAIE). He is a graduate of Sydney University (BSc First Class Honours, PhD) and the University of NSW (Master of Commerce).

Since 2014, Richard’s has been the Managing Principal of Mosman Resources, a private consulting business, specialising in the production and marketing of industrial minerals and chemicals. 

Cameron Perks 

Cameron (BSc Hons I) is currently industrial minerals’ (IM) Australian Correspondent, as well as the Managing Principal of CPIM Consulting, Australia. Cameron performs market analysis and research as well as the writing and research of news and feature stories, making a point to communicate extensively with all stakeholders. 

Previously, Cameron was an Industrial Minerals geologist (and geophysicist) for the Geological Survey of NSW (GSNSW), a State Government body, where he took the lead on various industrial mineral projects at the same time as performing a regulatory role.

Before joining the GSNSW, Cameron worked on SQUIDs at CSIRO, Australia’s federal government agency for scientific research.