CHAPTER XI 

 AGRICULTURAL LIME 



74. Sources of Lime. Lime is found in limestone 

 (mainly CaCOs) which is widely distributed over the United 

 States, principally as calcite, dolomite, marl, chalk, and 

 deposits of the shells of mollusks or other marine animals. 

 Limestone, when burned, yields calcium oxide, called quick 

 lime, which, when slaked with water and mixed with sand, 

 is made into mortar. Dolomite is rock composed mainly 

 of the carbonates of calcium and magnesium. Marl con- 

 sists of calcium carbonate mixed with clay, or peat in 

 varying proportions. Its calcium carbonate content ranges 

 from 5 to 90 per cent. 



75. Effects of Lime on the Soil. Lime is beneficial to 

 the soil on account of its chemical, physical, and biological 

 effects. Lime also acts as a direct plant food; for Cal- 

 cium is one of the ten elements necessary for plant growth, 

 although it is used by plants in less amount than is potas- 

 sium or magnesium. Any of the soluble salts of calcium 

 may serve to furnish the element calcium for plant food. 

 However, only three forms calcium oxide (quick lime), 

 calcium hydroxide (slaked lime), and calcium carbonate 

 (limestone) serve to correct acidity of the soil. The cor- 

 rection of acidity has an important influence on the devel- 

 opment of the bacterial flora, and it also assists nitrification 

 by furnishing a basic material to combine with the nitric 

 acid which is formed when the nitrogen of the air becomes 

 " fixed " or oxidized. 



The different compounds of calcium vary in their chem- 

 ical action upon soil. Calcium oxide, or quick lime, being 

 a caustic, is very active chemically. It decomposes organic 



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