New Zealand agricultural limestone: Fertilising middle earth

New Zealand exports over 95% of its total agricultural production and is the world’s largest dairy and sheep meat exporter. The dairy industry exports are mainly milk powder, butter and cheese and predominantly go to China, the US and the UAE and account for about 28% of New Zealand’s total exports

New Zealand agriculture

New Zealand livestock numbers for sheep, dairy cattle and beef cattle currently total about 40 million and are almost equally spread between the north and south island (Table 1). Almost 60% of dairy cattle are located in three regions; Waikato and Taranaki in the North Island and Canterbury in the South Island (Figures 1 and 2). Total dairy cattle numbers was relatively constant between 2002 and 2007 at about five million cattle and then grew to average about 6.5 million cattle between 2012 and 2015.

Table 1: New Zealand major livestock numbers 2015

Source: Statistics New Zealand

About 75% of New Zealand’s 29 million sheep are located in five regions: Manawatu-Wanganui and Hawkes Bay in the North Island and Otago, Canterbury and Southland in the South Island (Figure 3).

New Zealand soils are not naturally calcium deficient. However, it has been estimated that calcium removal from the soil by crops can range from 20kg/Ha for cereals to 150kg/Ha for kale. High producing dairy farms can remove 2.3kg/1000 litres of milk or about 50kg/cow per annum. 

New Zealand soils are said to be inherently deficient in phosphorus (P), sulphur (S), to a lesser extent potassium (K), and sometimes trace elements. Nitrogen fertilisers in particular can lower soil pH and fertiliser companies recommend the maintenance addition of limestone based on the type of fertiliser. Typical recommendations are 1.8 tonnes of limestone per tonne of nitrogen (N) in urea, 3.6 tonnes for di-ammonium phosphate (DAP) and 5.4 tonnes for sulphate of ammonia (SOA).

Initial application of agricultural limestone might be 2-3 tonnes/Ha to achieve a minimum soil pH of 5.5. Maintenance limestone application can vary with factors such as fertiliser type and application, rainfall, stocking and soil type but can be typically between 100-250kg/Ha/year.

Table 2: Ravensdown agricultural limestone quarries

Note: Liming Equivalent (LE) is the equivalent % (w/w) CaCO3 Source: Ravensdown Fertiliser Prices 11th July 2016

Figure 1: New Zealand Regions

Figure 2: New Zealand dairy cattle numbers 2015

Source: Statistics New Zealand

Figure 3: New Zealand sheep numbers 2015

Source: Statistics New Zealand

Most of New Zealand’s limestone deposits were formed in the Oligocene epoch some 22–30m years ago with some older limestones from the Ordovician era (or 450-500m years ago) common in the north-west Nelson area. Many of these older limestones, widespread in north-west Nelson, Takaka, Mount Arthur, have since been converted to marble due to granitic intrusions. Limestone deposits are also widespread throughout the Northland, Waikato, southern Hawkes Bay, Wairarapa, Westland, Canterbury and Southland areas.

In general, New Zealand’s limestones are high in calcite minerals, making them relatively dense and hard, suggesting a temperate origin.

Large resources of marble are present in Northwest Nelson and Fiordland.

Agricultural limestone production and producers

Agricultural limestone production in New Zealand has averaged about 1.6m tpa between 1970 and 2014 and was estimated to be 2.2m tonnes in 2014 (Figure 4). Between 2003 and 2012 annual production declined from 2.5m tonnes to about a million tonnes before recovering in 2013 and 2014 (Figure 5).

Figure 4: New Zealand agricultural limestone production 1970-2014

Source: New Zealand Petroleum & Minerals

Figure 5: New Zealand agricultural limestone production by region 2003-13

Source: New Zealand Petroleum & Minerals

Figure 6: New Zealand agricultural limestone production by region 2013

Source: New Zealand Petroleum & Minerals

Data for application of agricultural limestone data shows a steady decline of over 30% from 1.8m tonnes in 2002 to 1.2m tonnes in 2015 (Figure 7). Both production and application of agricultural limestone show the same overall downward trend. The main difference between the two sets of data may be some misclassification in the production figures.

Figure 7: New Zealand production and application of agricultural limestone 2002-15

Source: New Zealand Petroleum & Minerals & Statistics New Zealand

In the last decade one major change in the agricultural production sector has been the amalgamation of a number of limestone quarries by Ravensdown Fertilizer Co-op Ltd who, together with Ballance Agri-Nutrients Ltd, dominate the fertiliser supply industry in New Zealand. Ravensdown acquired their first limestone quarry in 1998 and now offer agricultural limestone from six quarries (Table 2). In 2012, the company claimed to be selling nearly 400,000 tpa of agricultural limestone or about one quarter of the current estimated total market of 1.5m tonnes (or 1.35m tonnes at 100% CaCO₃).

In July 2015 Graymont from Canada acquired the lime assets of Holcim (McDonald’s Lime and Taylors Lime) and became the second largest supplier of agricultural limestone from quarries at Opapure in the North Island and Makareao in the South Island. Total output of agricultural limestone from the two quarries is thought to be about 300,000 tpa.

Other major agricultural limestone producers are listed in Table 3 and the estimated market share of agricultural limestone producers are given in Figure 8. 

Figure 8: New Zealand agricultural limestone market share

Source: R Flook

Table 3: Other New Zealand agricultural limestone producers

Note: Liming Equivalent (LE) is the equivalent % (w/w) CaCO3 Source: Company reports, Fertmark

Product Specifications

The Fertmark Code of Practice, updated last in February 2016, for agricultural limestone specifies particle size with a minimum of 95% below 2mm and a minimum 30% below 0.5mm and a Liming Equivalent (L.E.) greater than 65%. For aerial application the size specification is changed; limestone with more than 95% below 2mm, more than 40% passing 1mm and no more than 2.5% below 0.5mm is deemed to pass the Civil Aviation Authority requirement that more than 80% of the load can be dumped in under five seconds.

It has become increasingly recognised that limestone particles above 1mm are essentially useless in a practical time scale but also conversely that fine particles below 0.5 mm are potentially hazardous in aerial applications. There have even been suggestions for removal of all particles below 0.5mm for aerial agricultural limestone application.

Bert Quin from Group One calls for finer limestone particle size specifications such as 100% below 1mm, 50% below 0.5mm and 25% below 0.25mm for normal spreading application.  However this may still be conservative. Field trials in Australia have shown that the minus 75 micron size fraction is twice as effective in acid soils as the 75-500 micron (0.075-0.5mm) fraction and three times as effective as the 500-1000 micron (0.5-1mm) size fraction. Despite differences in soils, climate, usage and so on it would not be surprising to see similar results in New Zealand.

Some agricultural limestone producers have already responded and introduced a fine spreading limestone with 100% of particles below 500 microns.

Prilled fine ground limestone (<100 micron) is also gaining popularity particularly for aerial application in hill country. It has been estimated (2010) that 40% of fertiliser in New Zealand was applied by fixed wing aircraft over an area of between 600,000 to 1.2m Ha mainly in hill country. The area of hill country which is mainly used for sheep and cattle farming is also increasing as more level land is increasingly converted to dairy farms. Sales of prilled fine ground limestone are estimated to have grown from their introduction in 2005 to be about 60,000 tonnes in 2015.

The increasing use of DAP, which has no calcium, rather than superphosphate in dairy farms is also prompting recommendations to apply 100kg/Ha of limestone with each P application which could be twice a year or 200kg/Ha/year of agricultural limestone which is twice the typical average application.

Application of 'dicalcic’ super (lime –reverted superphosphate) has also increased in popularity and although this material includes calcium there are doubts as to whether it is more cost effective than blends. One such proposed blend by Quin of reactive phosphate rock (RPR), elemental sulphur (S) and fine (<100 micron) limestone applied as a wetted mixture was estimated to be over 20% cheaper for the farmer.

All trends point in the same direction. Whether it is for spreading or aerial application, finer grades of limestone will be required to optimise their addition.

The second trend is the increasing closure of small quarries mainly due to increasing legislation relating to on-site qualifications and more rigorous quarry safety requirements particularly following the introduction of the new Health and Safety at Work Act in April 2016.