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Dolomite differs from Lime sand and Limestone in that it contains magnesium as well as calcium. It is used to supply both of these elements and is a very effective neutralising agent.  It is a carbonate limestone product that contains between 8-12% Magnesium as Mg and 18-22% Calcium as Ca.  Dolomite should contain less than 0.2% Sodium as well, so make sure you check this prior to purchasing.

In WA the focus has been to alter the pH of the soil, generally by applying calcium in the form of limesand or limestone.  However it is well documented that the elements of calcium, magnesium, sodium and potassium all influence the pH of the soil.  It is also fact that magnesium is up to 2.5 times more effective as a neutralising agent than calcium.

The ideal amounts of these macro-elements vary slightly, according to soil type, but as a percentage of the cations:

• the level of calcium should be between 64-75%,

• magnesium between 9-14%,

• potassium between 7-10% and

• sodium less than 7%.

Lighter soils generally have lower levels of all elements. It is possible to lock-up certain elements by having either too much or too little of these four macro nutrients in the soil.  For example, magnesium is required in order for plants to access phosphate, so low levels of magnesium can sometimes manifest as a phosphate deficiency!  There may well be sufficient phosphate levels available, but the plant is unable to access it because it requires magnesium to do so.

The application of calcium in isolation can induce a magnesium deficiency, even though calcium is a very important nutrient.  By increasing the amount of calcium in the soil, it effectively reduces the magnesium because it alters the ratio or balance within the soil.  Applying calcium to the soil in isolation can also reduce the availability of potash and phosphate, as well as manganese, boron, zinc and iron.  The balance between these elements is important, from a pH and a nutritional perspective, but also because they influence the soil structure.  Magnesium is quite mobile and deficiencies are more likely in lighter soils. Heavier soils are able to retain more nutrients, demonstrated by a greater cation exchange capacity. Lighter soils are less able to retain nutrients because they naturally have a lower cation exchange capacity.  For all of these reasons, it is essential that farmers undertake comprehensive soil analysis that provides a complete picture of their greatest asset and allow informed decisions to be made.

The best quality dolomite is sourced from limestone type rock, and requires crushing and screening.  End users need to check that the product is screened through fine screens – less than 3mm.  These products are generally considered to be more traditional dolomites.  They contain ratios of calcium and magnesium in line with those in the US and are lower in sodium, often with very high neutralising values.  Good quality dolomite should be talc-like in appearance and a pinkish-white colour.

Some of the dolomite sold in WA comes from lake systems, often salt lakes.  These can contain high levels of sodium, lower neutralising ability and are clay-based products which will turn to slurry when wet. The product is scarified from the lakes during the dry season and sold as is, or sometimes screened to take the larger clods out.

Lime WA Inc. is a group of limesand, limestone and dolomite producers who have developed a voluntary Code of Practice.  This was initiated to introduce clarity and consistency into the market.  This benefits the end user because it enables them to purchase product with confidence and to compare different products based on the same testing results.  It is a requirement of the Code of Practice, that complying pits test according to a strict set of guidelines and to report those results in a specific manner.  This eliminates the common practice undertaken by some pits where the levels of calcium and magnesium in their products are quoted as either a carbonate or an oxide, distorting the appearance of the results.  Complying pits must quote the elements in their products as a pure element. Pits working under the Code of Practice have accredited load cells on their loaders.  This is now a requirement for all pits, under the new weights and measures regulations.

Farmers should check the levels of the Ca and Mg as well as the levels of Sodium (Na), the neutralising values, particle size breakdown and the range for the pit. The particle sizing, combined with the neutralising value, gives an indication as to the speed at which the product will take effect, keeping in mind that the more acid the soil the product is applied to, the faster the reaction. Comprehensive soil analysis, from unbiased specialists with no vested interests, is readily available and not expensive.  When you consider that the land is the basis of your business, it follows that you should know and understand it intimately, as it will allow you to make informed decisions that will improve your land and productivity.

Watheroo Pit

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For any further information or bookings please feel free to email us using the contact form to the right, or by telephone:

Peter Manns - 0428 922 340

Terri Manns - 0418 922 340

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