Soil acidity F.A.Q.'s (Frequently Asked Questions)
Soil acidity in Western Australia
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The department recommends that lime is purchased from members of "Lime WA Inc" who practice a voluntary code of practice and supply product information sheets. For a list of Lime WA Inc suppliers please call their executive officer on 9752 3800.
Soil pH is currently used to assess the extent of soil acidity in the top and subsurface soil. When the soil is tested for pH, samples need to be taken from the topsoil and subsurface soil. Standard depths are the top 10cm for the topsoil and 10-20cm for the subsurface. For the soils with deep sandy profiles, an extra sample needs to be taken in the 20-30cm layer to find out the origin of the acidity. Aluminium becomes more soluble under acid conditions inhibitions root growth in plants. A measurement to test for Al has only been calibrated for the Wodjil soils of the eastern wheatbelt. Until a universal test for Al is available, measurement of soil pH is presently the cheapest and most effective way of assessing the extent of soil acidity.
Testing of lime samples can be done through the Chemistry Centre in East Perth or Ultra Trace in Canning Vale. Tests for Neutralising Value (NV) and particle size can be done.
CSBP carry AUSPAC and/or NATA (National Accredited Testing Authority) accreditation for the laboratory tests they conduct. The tests are well calibrated for WA soils and can be viewed as reputable data.
Contract your local Department of Agriculture office.
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Through rural merchandise companies
Dolomite is less reactive in the soil than limesand for the same neutralising value (due to the Magnesium content which reduces the dissolution rate).
The rate at which it dissolves will also depend on the fineness of the product. The finer the particles, the higher the total surface area of the particle exposed to the soil solution and the more rapidly they will dissolve.
For carbonate based liming materials such a dolomite, limestone and limesand, particles greater than 1mm-2mm in diameter will not dissolve quickly enough to affect soil pH within 10 years of application. In most circumstances limesand will be the finer of the three materials and will have a higher Neutralising Value (NV).
No. Lime is only very slightly soluble in water. Going cloudy is not dissolving and does not show how good it is. Ask for neutralising information.
Lime for lime pelleting of seed with Rhizobium should be bought specifically for that purpose.
When using products containing hydroxide caution should be taken. A pH of 9-10 (5g of lime in 50mls of water) or greater will kill rhizobium. The Neutralising Value is not a safe indication of a lime products toxicity to rhizobium.
G-lime is lime kiln dust pelletised with water, then recrushed. It is a mixture of the less reactive calcium carbonate and the more reactive calcium hydroxide, but it typically has an NV of 90.
Generally G-lime, burnt-lime or lime kiln dust, and hydrated lime are too alkaline and will kill the rhizobium being coated on the legume seed.
Gypsum is calcium sulphate and is used as a source of sulphur as well as a soil ameliorant for dispersive soils. Dolomite is used to ameliorate soil acidity and has some levels of magnesium in it but not enough to justify its use solely to build up magnesium levels.
The quality and effectiveness of lime products varies. Quality is measured by the Neutralising Value (NV) and the fineness of the lime. The higher the NV the better and the finer the product the better. After this you have to check the end product cost of each product to get value for money. ie. Cost delivered and spread.
Some industrial sources such as burnt-lime, the off-product from cement production, is more reactive in soils and the atmosphere than natural limestone or lime sand.
Burnt-lime is more reactive because it contains hydroxide forms of calcium rather than the less reactive carbonate forms that are found in limestone and limesand. Calcium carbonate is a more stable, slower reacting lime source needing larger rates of application less often.
Burnt-lime that has been exposed to the atmosphere for long periods may have already reacted with the air to form less reactive compounds of calcium carbonate. Quality tests should be done regularly by the supplier and asked for by the buyer to ensure the product is value for money.
The type of lime isn't as important as when and how much lime is applied. It is more important to start the liming process earlier so that the lime has time to leach down the profile.
Higher rates (up to 2 t/ha of good quality lime (neutralising value more than 75%) incorporated into the top 10cm can be used.
However, caution must be taken where nutrients such as manganese, copper, zinc are marginal as lime can induce deficiencies of these micronutrients.
Keep in mind that pH changes will take at least 4-7 years longer for the lime to move down the profile and changes in pH will be smaller (0.1 to 0.5 units).
The top soil needs to be maintained above pH 5.5 to ensure some downward movement of lime to treat subsurface acidity.
Lupins are moderately tolerant of soil acidity. Applying lime where some of the micronutrients including manganese, zinc and copper are marginal may cause lupins to perform poorly.
Addressing the micronutrient deficiencies particularly manganese will help alleviate the problem.
No, the acid dark grey peaty sands on the swan coastal plain and along the south coast that occur in wet or swampy areas contain low levels of aluminium in comparison to mineral soils. Common vegetation in these areas include tea-tree, bottlebrush or kangaroo grass.
Lime at rates as high as 2 t/ha and rock phosphate fertilisers are useful in improving the establishment of subterranean clover pastures.
Not directly. By improving soil health, lime will increase microbe activity that will help in building and maintaining soil structure over time.
Gypsum is used to improve the structure of dispersive/sodic soils at rates as high as 2.5-5.0 t/ha by aiding in soil aggregation and hence structure and permeability.
The best time to apply lime will depend on your budget and when it best suits getting lime delivered. Because the main cost of lime is the carting cost, times that coincide with back-loading would be ideal. However, storing and applying lime in dry conditions in summer or autumn without incorporating can result in lime being blown by the wind.
In terms of its activity in the soil, the best time would be after a couple of rains which will moisten the soil and make it easier for incorporation by a tine or implement prior to cropping. This moisture would also allow the lime to begin ameliorating soil acidity. However, the benefits of lime are most significant after 2-3 years of application, although with good incorporation, soil moisture and low soil buffering capacities, benefits may be seen after one year.
In summary the sooner the better, but consider cost cutting measures such as back-loading and beware of dry and windy conditions.
Fertiliser recommendation systems in WA have classically used the "sufficiency" method of determining macro-nutrient cation (calcium, magnesium and potassium) requirements of crops. There is a growing controversy in WA agricultural circles on the importance of the "base saturation method" to the extent that farmers are sending soil samples out of the state and even overseas for analysis and advice. There is no dispute that base saturation and its implications for cation availability is a well established principle. However it is open to question as to whether the application of quantitative base saturation targets, established overseas on less weathered soils of higher clay content, is relevant to WA soils.
In WA soils range from highly leached, cation impoverished acid sands to cation-rich alkaline mallee soils where topsoils are Ca-dominant and subsoils Mg-dominant. There is therefore good reason to anticipate that both cation deficiencies and cation imbalances will occur in WA soils and limit plant production. There are no systematic WA data relating soil cation status to plant uptake of cations and grain yield and quality. Overseas experience indicated that soil and foliar testing for cations can be an essential component of monitoring programs for maintaining soil fertility (sustainability).
With cereal and pasture hay crops and assuming no acidifying fertilisers are added, 5t/ha of hay will remove 150kg/ha of lime and 10t/ha hay will remove 300kg/ha.
Firstly you must get your soil tested to determine whether the topsoil pH is the problem or the subsoil pH.
Generally, for managing acidity in the topsoil on a sandy loam (organic matter < 1.5%) in the medium to high rainfall area (> 325 mm/yr) apply 1t of high quality lime (NV 85-95%) per hectare when the pH (in CaCl2) is 4.2-5. This should be done every 7-10 years depending on the pH change over time. Applying 1t/ha will result in a pH rise of 0.5 to 0.7 units in the top 1-10cm of soil.
If soil pH is lower in the subsurface, a liming program must be adopted well before soil acidity reaches critical levels in the topsoil, because lime will take time to leach down into the subsoil.
Applying rates of high quality lime over 1.5t/ha should be done with care. Before embarking on a liming program levels of trace elements must be adequate as liming can induce deficiencies of copper, zinc, and manganese (seen in narrow leafed lupins) and iron (usually only a problem for pastures grown on very sandy soils in very high rainfall areas).
The pH you start liming will depend on your most acid sensitive crop/pasture in your rotation.
All pH values mentioned below were tested in 1:5 soil/CaCl2 solution. If tested in water the values are approximately 1 pH unit higher.
Acid sensitive crops include Lentils and Faba beans (critical pH 5-6).
Acid sensitive pastures include Strand, Barrel and Burr medic as well as Lucerne (critical pH 5-6).
Moderately sensitive crops include Chickpeas, Albus lupin, Barley, Canola, sensitive wheats and Field peas (critical pH 4-5).
Moderately sensitive pastures include tolerant wheat, Triticale and Oats (critical pH 4-4.5)
Tolerant crops include Narrow-leaf lupin (critical pH 4.0)
Tolerant pastures include Yellow and Cadiz Serradella (critical pH 4.0)
If subsurface pH is the problem, liming should begin before the topsoil pH has reached critical levels. The topsoil in this case would have an approximate pH ( in calcium chloride) >5.5.
Lime incorporated into the top 10cm can affect the subsurface pH with time. Changes in pH will be smaller (0.1-0.5 units), and it may take four to seven years longer for the lime to move down the profile.
To ensure results from test strips there a number of guidelines and steps
Soil pH can be lowered by applying elemental sulphur, aluminium sulphate or sulphuric acid but these methods have not been tested in WA and are unlikely to be economic for broad scale farming systems (as opposed to horticulture). In general, agriculture is an acidifying process through product removal and the use of some nitrogenous fertilisers, although the time scale over which alkaline soils are neutralised could be hundred of years.
Lime will only affect acid-tolerant rhizobium when applied directly through lime pelleting. Lime application done for the purpose of ameliorating soil acidity at rates 1-2t/ha will not affect the rhizobium.
G-lime is lime-kiln dust pelletised with water, then recrushed. It is a mixture of the less reactive calcium carbonate and the more reactive calcium hydroxide, but it typically has an NV of 90.
When using products containing calcium hydroxide caution should be taken. A pH of 9-10 (5g of lime in 50mls of water) or greater will kill rhizobium. The Neutralising Value is not a safe indication of a lime products toxicity to rhizobium.
Generally G-lime, burnt-lime or lime kiln dust, and hydrated lime are too alkaline and will kill the rhizobium being coated on the legume seed.
Gypsum (calcium sulphate) is used to improve the soil structure of dispersive soils and has no ability to neutralise acid in soils. Gypsum and lime blends would suit an acidic and sodic soil with a high exchangeable sodium percentage.. Usually sodicity is linked to alkalinity but not all sodic soils are alkaline. Occasions where there is a need for gypsum and lime blends may be in the dairy industry where heavy traffic causes a loss of soil structure and where pH is low.
Gypsum and lime blends may also be used where there is a requirement for sulphur and it is required for a quick response. Adding elemental sulphur in this case would cause acidification and it will not be as readily available. Crops such as canola require high levels of sulphur.
Lime will ameliorate soil acidity relatively quickly when incorporated into the top soil with a tined or disc implement. The more it is mixed in the soil the quicker the response as more lime is in contact with the soil and soil solution.
Under no-till, the rate at which lime acts in the subsoil could be decreased.
In terms of heat the answer is yes. Lime is a stable substance that requires higher temperatures than stubble burning to change form. Burnt limes and lime kiln dust are the by-products of cement making which involves very high temperatures.
In terms of wind erosion, burning will mean that there is less protection and the risk of losing applied lime is greater if it hasn't been incorporated.
Lime can easily be blown by wind and people have tried different methods of storage to prevent this.
Haybales have been used to contain the lime and provide a buffer to the wind.
There has also been some success by mixing agras or similar fertiliser and water (1 part agras to 5 parts water) and spraying it over the lime heaps.
While it is beneficial to have most of your lime with particle sieve ranges from 0.1-1mm so that it reacts in the soil in useful time, very fine lime material (particles <0.1mm) seen in products such as burnt lime can be difficult to apply evenly due to wind carry.
In this case some moisture in the product will assist in spreading as wind carry is prevented.
Calibration of spreaders is recommended.
Page reviewed November 2006
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