Neutralising Acid Rainfall

Animal feedstuffs frequently contain finely ground calcium limestone as a source of calcium. In general, high purity products with low levels of toxic impurities (e.g. with lead levels below lOmg/kg) are specified [10.4], 

Poultry require grit in their gizzard to help them grind their food. Closely graded limestone and shell products in the size range 3 to 10 mm are generally specified. 

and particularly conifers, do not require liming as they prefer acid soils and can tolerate pH levels below 4. They are, however, more effective at removing acidic pollutants from the atmosphere than shorter crops and are frequently grown on acid and poorly buffered soils. As a result, water draining from forested areas is frequently very acidic (see section 10.6,3.1). 

Applications of agricultural limestone are used to raise the pH of streams draining forested areas. The limestone is spread in a very finely divided form (e.g. 50 % less than 10 pm), at about 15 tonnes per hectare [10.2], over the boggy areas in the headwater regions of sensitive catchment areas. Such areas are generally left unplanted so the limestone does not adversely affect tree growth. Regular repeat applications are necessary. 

While spreading limestone may improve stream water quality, it can have an adverse effect on certain plant species (e.g., mosses and lichens) in the areas in which it is applied. In some areas, therefore, conservation requirements may prevent its use. 

---