There is a school of thought that dolomite should not be applied in situations where soil calcium levels are near ideal because dolomite as well as containing 11.5% magnesium also contains 24% calcium.
In theory that appears sound, however the reality is quite different. In situations where soils have been limed this autumn it is almost inevitable that plant available magnesium levels will have declined.
In this situation dolomite still remains the most effective magnesium fertiliser available. Scientific studies at Massey University show the release of magnesium from dolomite at the end of twelve month to be significantly greater than magnesium from unreacted serpentine.
The other more soluble magnesium products, calcined magnesite (MgO) and Kieserite (MgSO4) are likely to lift plant available magnesium levels in a short period after application, however due to their solubility, they are also prone to more rapid leaching.
If the purpose of applying magnesium fertiliser is to minimise and eventually eliminate calcium/magnesium related magnesium disorders, particularly in dairy cows just prior to calving and in the three months of peak lactation after calving, dolomite is the most effective magnesium fertiliser available.
In our twenty years of our work with farmers dolomite applied at 220 -250kg/ha has always lifted magnesium levels in pasture plants sufficiently to ensure that when animals are well fed on a balanced diet and the rumen is functioning efficiently few suffer severe calcium/magnesium related metabolic problems in spring.
When dolomite is applied at 250kg/ha, 60kg/ha of calcium is applied. Being in the carbonate form the release rate is steady, with plant tissue calcium levels in rye dominated pastures constant at around 0.60% with magnesium levels rising to between 0.22 and 0.25%.
When soils are well structured and biologically active there is an ongoing demand for calcium. Calcium is a major constituent of milk and bone, so whether the primary requirement is milk production or growth the calcium provided is beneficial in maintaining calcium availability.
The key to optimum performance is the balance between calcium and magnesium. Prior to calving the requirement for calcium is less than when milking. In dolomite treated pastures the demand for more calcium after calving is often met by the increasing percentage of clover in the sward.
Phosphorus is an essential element in animal nutrition and magnesium acts as a carrier for phosphorus. Again dolomite helps ensure a balance of required major elements essential for optimum pasture growth and animal performance.
Keeping a constant ratio of minerals in pasture is an essential part of ensuring optimum animal health and performance. Because dolomite is a carbonate the release rate follows the natural increase of pasture growth in spring.
When soil temperatures are low the release of both calcium and magnesium is sufficient to meet plant requirements, with lifting growth rates due to increasing soil temperatures in spring the rate of release of both calcium and magnesium increases accordingly.
If the aim is to maximise pasture and animal performance this coming season without time spent treating cows down with calcium/magnesium related disorders, dolomite remains the most effective product available. Its local, it’s immediately available, and provides protection for at least twelve months.
As the late Prof Walker wrote “…. individual farmers will have to make their own calculations, but in my view dolomite is the ideal material to use on acid soils low in magnesium….”
For more information call us on 0800 436 566.