WHAT IS DOLOMITE?
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 neutralizing agent. It is a carbonate limestone type product that should contain 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.
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 preferably 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 neutralizing 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 neutralizing ability and are clay-based products, which will 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 or sticks out.
WHY SHOULD I CONSIDER DOLOMITE?
In WA the focus has been to alter the pH of the soil, generally by applying calcium in the form of lime sand or limestone. However we believe that the pH of the soil is like a temperature gauge – it tells you the acidic state of the soil, but it doesn’t tell you what is causing the problem. It is well documented that the elements of calcium, magnesium, sodium and potassium all influence the pH of the soil. Magnesium is also up to 2.5 times as effective at neutralizing acidity 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 on 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.
WHY WATHEROO DOLOMITE?
Watheroo Dolomitic Lime contains high levels of calcium and good levels of magnesium. It also has some of the lowest sodium levels of any local liming product currently on the market in Western Australia.
It is excavated, then crushed and screened, giving it a greater range of particle sizing than lime sands. Traditionally Watheroo Dolomite has approximately 40-45% of its particles under 125 micron, a size range that is important in determining how quickly the product works. The surface area of a small, irregularly shaped particle is greater than that of a larger, uniform particle, allowing the acid in the environment greater opportunity to break the particles down.
Our product is crushed and screened through 2mm screens for agricultural use, producing a very uniform result. We are an Accredited Lime WA Inc operator and our product is tested regularly, according to the requirements of the Lime WA Inc. Code of Practice. We are also randomly AUDIT tested by the Department of Agriculture at least every second year. A Departmental Officer completely independently of us conducts these tests.
This allows the purchaser to buy with confidence, knowing that the specification sheet they are provided, accurately represents the product that they receive. Code of Practice Members all test according to the same criteria, at the same laboratory, allowing customers to accurately compare products and make better buying decisions.
Appointments are necessary for loading, although we try to be as accommodating as possible. We do ask that trucks are cleaned down prior to coming in to the pit, as it is on an operational farm and we like to remain on good terms with our neighbours! Accounts will be sent out via email or post on thirty day terms to approved customers only. We use trade certified loader scales and the product is weighed into the truck for bulk product. The product is invoiced from the loader dockets.
WHAT SHOULD I BE LOOKING FOR?
Farmers should check the levels of the Calcium (Ca) and Magnesium (Mg) as well as the levels of Sodium (Na), the neutralizing values, particle size breakdown and the range for the pit. The particle sizing, combined with the neutralizing 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.
The lime calculators that are currently widely used by advisors and companies selling products are based purely on pH change and use a weighting system that discounts any larger particle sizes as virtually worthless and calculates all particles under 500 micron at the same effectiveness. We don’t have any problem with the argument that larger particles take a long time to work, but given acid environments and time –particularly if the paddock happens to be cultivated, they will still slowly impact the pH. Our other concern with the calculators is that the very finest particles (which lime sands have very little of) should in our opinion be given a higher weighting on the calculations, which they are not.
Comprehensive soil analysis, from unbiased specialists without 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.
Contact us for further information as to where you can obtain independent, comprehensive soil tests – these have no connection to us and we receive no “kick-back”. (And no guarantee that you will need dolomite either!). We just want to see growers get good information.
WHAT IS LIME WA?
Lime WA Inc. is a group of lime sand, 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 previously 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.