Friday, 12 February 2016

Science of lime saves wasting time


Aglime is essential to the sustainable productivity of New Zealand farming systems and vital in optimising soil health and pasture growth.

But lime is in danger of being taken for granted. Without it farmers are faced with an inability to modify soil acidity and alkalinity. This affects the soil’s ability to absorb nutrients and ultimately puts the nation’s fertiliser investment in jeopardy.

As a general guide, maintaining optimum pasture pH between 5.8 and 6.0 means an annual lime application is needed at a rate of 350-500kg/ha for dairy, 250-400kg/ha for dairy support and 100-300kg/ha for dry stock.

While lime is indispensable, it’s worth considering that not all limes were created equal.

To avoid wasting time and money on lime comparisons, there are three factors to consider.

Calcium carbonate content

Calcium carbonate (CaCO3) is the active ingredient when it comes to altering pH. This varies throughout the country from 99% to 65% CaCO3, depending on local geology. A lower CaCO3 lime will be needed in larger amounts to achieve the same effect. Lime with an 80% value will need to be applied at a 12.5% higher rate than a lime with a 90% value. At around $30 per tonne, it pays to know the contents.


The solubility, or dissolution rate of the CaCO3, is largely dependent on the particle size of the lime - the finer the particle the quicker it will react. Hardness or porosity are less important influences.

But fineness itself does not increase the total liming effect; the amount of CaCO3 required to neutralise a unit of acidity in the soil is fixed. A combination of fine and coarse particles will neutralise acidity over an extended period of time.

Moisture content

Many limes have a relatively high naturally-occurring water content level. In the South Island several Ravensdown quarries dry the raw lime, prior to processing, to allow it to be crushed to required specifications. This results in a low water content in the final product, often around 1 to 2%.

Farmers don’t want to have to pay for transporting tonnes of H2O in their lime. And depending on how the CaCO3 level is stated, it could also mean that they are buying water at the expense of the active ingredient.

A Fertmark-certified product has been assessed as having the water and calcium carbonate levels that it declares. So it pays, in terms of time and money, to look at the science behind aglime.

There is a fourth and final factor. Is the lime safely sourced? Lime quarries are investment-intensive operations and, to be safely sourced and processed, they need practical measures like guarding around machinery, geotechnical stability, staff training as well as a safety-first culture.

As owners of eight out of the nation’s 70-80 quarries, we encourage both customers, and quarry managers, to put lime safety on their agenda in order to sustainably deliver this vital soil conditioner long into the future.