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Lime Quality

 

Given recent increases in fuel costs, the most important lime decision is for growers to choose the best quality lime.  Although some people try to confuse the issue, understanding lime quality is very basic.  There are only 2 key quality issues

 

1. Neutralising value, which is essentially a measure of purity.  Most limes sold in WA range between 70 and 95% pure, and hence have a neutralising value in that same range.  The neutralising value represents the percentage of CaCO3 in the lime, which is proportional to the amount of acid the lime can neutralise.

 

2. Particle size is a most important factor especially in low rainfall WA. The following extract is from a paper titled Particle Size Determines the Efficiency of Calcitic Limestone in Amending Acid Soil by very highly credentialed agricultural scientists in the eastern states (B.J. Scott, M.K. Conyers, R. Fisher and W. Lill) that was published in the Australian Journal of Agricultural Research, Vol. 43 1992.

"The six particle size fractions were derived from a 98% pure calcitic limestone from the Marulan Quarry in New South Wales. At a given rate of application, the finer the particle size, the greater the increase in pH. This trend applies even at the 10 t/ha application rate where we expected the fineness would be of less importance." This was one of the few trials that compared the same product crushed to different fractions of fineness. The greater increases in pH with finer lime lasted for at least three years and were highlighted by increased yields.  Coarse fractions were relatively ineffective, demonstrating the fallacy of a commonly held belief that the larger lime particles impart a longer benefit because they dissolve more slowly.

 

Limes dissolve in soil by acid eating away the surface of the lime particle. When the acid attacks the surface of the lime, carbonate is released and that neutralises the acid. As a result, the soil next to the lime particle is neutralised and can’t dissolve any more lime. The lime particle sits in a pocket of neutralised soil and is no longer effective.  Large particles of lime never dissolve as they are encased in a film of neutralised soil.

 

Lime will not dissolve in a neutral solution. If lime dissolved in water, why would limestone rocks be used for seawalls?

These types of field assessment of lime reactivity have been completed all over the world.  The outcomes are always the same.  Limes with a higher proportion of small fine material have more capacity to dissolve and therefore increase soil pH.  

 

This is why Aglime is the best lime in WA.