100 CHEMISTRY OF FARM PRACTICE 



is danger of depleting the organic matter in soils which 

 are not well supplied with it, but this does not hold true 

 for applications of calcium carbonate. In soils moderately 

 well supplied with organic matter, the use of heavy appli- 

 cations of caustic lime may lead to the liberation of more 

 available nitrogen than the plants can use. In this case 

 some plant food, especially nitrogen, will be lost. Exces- 

 sive applications of caustic lime, even to clay soils, may 

 lead to the flocculation of the clay to such an extent that 

 percolation will be too rapid. The flocculating power of 

 lime may be illustrated by adding lime water or milk of 

 lime to water containing clay in suspension, when it will 

 be observed that the clay particles rapidly settle out. 



Caustic lime, when applied excessively, may exert a 

 harmful effect on the soil bacteria, and temporarily arrest 

 to some extent the useful functions performed by these 

 agents; but this form of lime, when applied in moderate 

 amounts, is usually quickly changed to a neutral salt, 

 either calcium carbonate or calcium silicate. The former 

 salt is still effective to correct acidity, but calcium silicate 

 does not exert such an influence. 



The fact that continuous liming without manure makes 

 land less productive than it formerly was, has led many 

 people to object to the use of lime altogether. The initial 

 application of lime produces such marked results, due to 

 its influence on the stored plant food in the soil, that the 

 fact that its effects are indirect is not recognized and there 

 is a temptation to continue its use at the expense of the 

 potential fertility of the soil. It is very unusual for the 

 soil to contain such an insufficient supply of lime that 

 lack of calcium becomes a limiting factor in plant growth. 



76. Shipping Lime. The main forms of lime marketed 

 for agricultural purposes are " quick lime " (CaO), " water- 

 slaked lime " (Ca(OH) 2 ) and " air-slaked lime " (CaCO 3 ). 

 To ship agricultural lime a long distance involves large 

 expense, due to freight charges. A ton of water-slaked 



