Agricultural lime... some facts and recommendations

Waimarino Bulletin, Volume 2, Issue 1, 5 June 1984, Page 6

Agricultural lime... some facts and recommendations

There are several factors about agricultural lime that are not often fully understood. This article is the first in a series on the different types of lime, what the buyer should look for regarding quality, the effect of lime application and a brief summary of results of lime trials. In the North Island there are three major types of lime deposits. The North Auckland limestone in the main is softer, and easier to quarry. The majority of suppliers have a lower than average price for their lime but this is cancelled out by lower calcium carbonate levels. The deposits stretching from north of Raglan down

the western-coast to south of Pio Pio are difficult to work due to the requirement for drilling and explosives. In the South Eastern (Southern Hawkes Bay to the Wairarapa) area the limestone deposits are of a broken shell type which are easy to extract but difficult to grind. Most deposits were formed over 20,000,000 years ago. There are no commercially worked deposits in the Bay of Plenty, Taranaki or Manawatu areas. Since the inception of transport subsidies the Ministry of Agriculture has insisted on all lime that subsidy is paid out on is to a certain standard. One requirement sets out calcium carbonate levels and the other the fineness of grinding. Firstly let us look at the calcium carbonate (CaC03) standard. To meet MAF standard a quarry in the South Auckland to King Country area must reach a level of 80%. Random samples taken by MAF officers are sent to Ruakura for official sampling. The last four recorded from Waitomo and Wairere Lime Companies were from 9097%. This is a very high level but good news for the purchaser. The vital neutralising element is calcium carbonate. A purchaser of lime should look at the landed cost on the paddock

then work out his unit cost with the percentage. An example: Cost per tonne say $30. Level of calcium carbonate 92% =$32.60 for 100% as against at say 82% lime = $36.58 for 100%, obviously the higher quality is the better buy. The second major factor with the MAF standard is fineness of grinding. No more than 5% by weight is permitted of a size of 2mm or moref 1/12 inch). At least 50% must be able to pass a 0.5mm sieve size. This is a fine dust. There are very good reasons for this size

standard. Limestone becomes useful in the soil when the moisture becoming acid comes in contact with the alkali particle. The finer the particle size the more contact there is with the soil. Large particles remain in the soil completey useless for years. Basically the finer the lime the better it is. Unfortunately very fine lime is difficult to handle and to spread. The MAF standard is a compromise which has already had minor alterations. To sum up look for a high calcium carbonate level with a fine particle size.