Understanding Lime Product Effectiveness

There are various liming products available to growers to raise soil pH with ground calcium and magnesian limestone being the two most common raw materials. Quarried rock is ground and sieved to meet industry standards set by AgLime Quality Standards with limits set on the highest particle size and percentage of dust. 

The effectiveness of a liming product is measured by its Neutralising Value (NV). This is a laboratory determined test which gives the liming value as a percentage calcium oxide. Calcium and magnesian ground limestone is typically 50-55% NV. 

Calcifert and G-lime are examples of a granular lime product and is made from calcium or magnesian limestone flour which is then reformed into a hard spreadable granule with a size range between 2-5mm. The benefit to growers is it can be spread by a conventional fertiliser spreader and allows a grower to apply using their own equipment. The manufacturer claims the hard nature and regular size of the granule allows it to be spread evenly up to 36m. NV range from 52-54%.  

Such granular products are popular for small applications variably spread to address pH hot spots identified by GPS sampling. The can also be used as little and often applications for any crop. They do have a high relative cost per NV percentage and better targeted at high value crops such as vegetables. 

Tables are available to calculate the amount of lime required to raise a soil to a desired pH. Soil texture is an important factor with clay soil requiring more lime product when compared to a sandy soil. 

Lime Requirement Values (tonnes/ha product based on 50% NV) 

It is important to note that a similar total quantity of lime will be required for a granulated product such as Calciprill or G-Lime to raise the pH to target. The lower rates recommended by suppliers for such products are required on an annual basis to raise pH to the same target level over time. Equally the reformed granule does not simply dissolve into the soil. It requires moisture and weathering to break down and in dry conditions will continue to sit on the soil surface.