There is a lot of talk in the market about the effectiveness of granular and prilled lime over normal powdered ag lime.
Given the ag lime is milled down before the prilling or granulating process, it makes the product faster reacting in the soil which will provide a faster response.
This faster reaction doesn’t mean you can use 80% less product to move your soil acidity up the pH scale. Whilst the initial pH change over the first few months will be greater using prilled lime, bulk ag lime applied at a higher rate will continue to neautralise the soil further over the next few years (~70% in 1yr).
Example 1: For slight soil pH adjustments or to maintain soil pH you maybe able to apply 300kg/ha of prilled lime to achieve your result. Sugar cane growers have been getting good results banding 300kg/ha or prilled ag lime, but they are doing it every year compared to broadcasting bulk ag lime once every say 3 years.
Example 2: However a broad example by DPI to move the pH of the top 10cm of soil from 4.0 to 5.3 CaCl2, you would have to apply 2.4t/ha of bulk ag lime with a NV >95 (see table below). To reduce the soil acidity further to 5.5 you would to apply another 0.4t/ha for that particular soil CEC.
Other factors such as incorporation can also increase effectiveness of ag lime. In ideal conditions, lime might move approximately 2cm per year, and will take five years to reach 10cm. Incorporating bulk lime will amend the top 10cm, and therefore, yield increases are likely occur for up five years until surface lime catches up.
If you have Soil acidity constraints it is best to be proactive, especially in clay soils. Correctly sub soil acidity from 4.0 is a substation job to ameliorate and correct the soil pH. For pH adjustments you are best to concentrate and correct the issues in a few paddocks each year, rather than spread a small amounts of lime every year on all your country. Depending on soil type, crops and fertiliser inputs, liming might be required every 5-15 years.
Remember always seek advice from your local agronomist to achieve the best results in correcting soil constraints.
Source GRDC 23th Feb 2022
