“We can no longer afford to think in terms of N P and K; we must include S and Mg.” This statement is from an article titled, Magnesium – Cinderella of NZ Agriculture, written 50 years ago by M.R.J. Toxopeus a scientist at the Ruakura Research Centre.

The continued application of superphosphate containing more sulphur than phosphorus, and the inclusion of elemental sulphur where necessary, has largely attended to sulphur requirements since then, but little has been done to address magnesium deficiencies.

And the cost to dairy farmers continues to mount each year.  Cows showing early symptoms, such as hyperactivity and going down in spring, incur the immediate cost of treatment and lost production. If the animal dies, the value of the cow and her production for the season is an added cost, and often there is also the loss of a valuable calf.

However, the issue most often spoken of by farmers is the frustration of not knowing when a cow may be down out in the paddock, the severity of her situation, and the time required to treat and get her mobile again.

Minutes are precious on a dairy farm in spring, so time spent treating animals is time away from another essential task, and reserves of human energy become increasingly depleted.

A single cow requiring treatment almost certainly means there are several others producing below optimum, and when this cost is also added, the dollars lost through calcium/magnesium related problems in spring become considerable.

Professor Tom Walker of Lincoln University in 1997 wrote, “What New Zealand farmers must appreciate is that Mg, like cobalt and selenium, may be necessary on many soils for the sake of animal health, rather than to improve pasture growth, and it makes good sense to correct animal deficiencies through the soil and the plant….and in my view dolomite is the ideal material to use on acid soils low in Mg.”

There is only one deposit of dolomite in New Zealand, at Golden Bay in the South Island, and although there are an increasing range of magnesium products available to farmers, when it comes to minimising metabolic disorders in milking cows in spring, there’s nothing as effective as dolomite.

The reasons for dolomite being the most effective product available are due to a number of factors.  Both calcium and magnesium are involved in cows suffering in spring and dolomite contains 11.5% magnesium, and 24% calcium, both in the carbonate form.

It’s also a natural product, originally a sea bed deposit containing a wide range of trace minerals, including boron, cobalt, copper, manganese, molybdenum, and zinc.  Although these occur at only very low concentrations, when soils are deficient in trace minerals they are valuable.

The effect of dolomite lasts at least twelve months and is typically applied at a rate between 200kg and 260kg/ha (23kg and 30kgMg/ha). Because of the single source of supply the cost per hectare varies throughout the country.  However, although it has been seen by some  as expensive compared to ordinary lime, the cost benefit in pasture improvement and animal health is far greater.

Because of its purity and compactness dolomite is finely ground, with 62% less than 150 microns, which means that it becomes available for plant uptake within a very short time after application.  Recommended application time is a month prior to calving, which gives a marked improvement in herd health and performance.

Dolomite may be added to most fertiliser products or, as is increasingly common, delivered bulk direct to farm, with a truck and trailer load sufficient for around 100ha.  For more information call Peter on 0800 436 566.

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