Liming Materials

The Fertilisers Regulations 1990 Group 5(a) describes about 21 types of liming material, and Group 5(b) covers any not specified in Group 5(a). These regulations set limits for the content of MgO and the percentage which will pass through various sieve mesh sizes. They also give the essential value/s that must be declared. This is always the neutralizing value, and sometimes the percentages passing through various sieve sizes. An example is magne-sian (US: magnesic) ground limestone. The meaning of this term is defined as 'Sedimentary rock consisting largely of calcium and magnesium carbonates and containing not less than 15% of magnesium as MgO and of which 100% will pass through a sieve of 5 mm, not less than 95% will pass through a sieve of 3.35 mm and not less than 40% will pass through a 150 micron sieve.' The declared values are 'Neutralizing value', and 'Amount of material as a percentage by weight that will pass through a 150 micron sieve.' The latter value is commonly called a determination of fineness of grinding. The stated values may vary by 5% from the measured values. We will describe the method for determining moisture, neutralizing value, and fineness of grinding as given in the SI 1996 No. 1342, The Fertilisers (Sampling and Analysis) Regulations 1996, Schedule 2 Part II, [5.2. Determination of moisture, 5.6. Determination of the neutralizing value in liming materials, 5.7. Determination of fineness of products other than potassic basic slag], and indicate in brackets where the AOAC method differs. The AOAC methods for agricultural liming materials are given by Johnson (1990a), and include methods for assessing carbon dioxide, silica and oxides of aluminium, iron, phosphorus, and titanium; also elemental aluminium, calcium, iron, manganese, magnesium, phosphorus, silicon and sulphur as sulphide.

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