64 Report of the Department of Agronomy of the 



solubility of limestone. 



Under natural conditions limestone (calcium carbonate or calcium 

 and magnesium carbonates) is more soluble than most other soil 

 constituents and is easily leached away. The easy solubility of this 

 material is illustrated by the fact that the lime carbonate in many 

 feet of limestone has often been leached away to form one foot of 

 soil, which is made up mainly of the impurities contained in the 

 lime rock. Also the caves and sink-holes found in limestone regions 

 are due to the dissolving away of the rock by underground waters. 

 In an even more forceful way the solubility of limestone is illustrated 

 by the large quantities of it contained in spring and well waters, it 

 being the material which makes such waters hard and which is 

 deposited as a crust in kettles and boilers when the water is evap- 

 orated. As a consequence of the comparatively easy solubility of 

 lime carbonate the great majority of soils in eastern United States 

 not naturally well stocked with lime, and, especially those long 

 cultivated, are now deficient in that material. The processes of 

 cultivating and cropping tend to cause a more rapid leaching of 

 lime from the soil as well as removing it in crops. Even limestone 

 lands when long cultivated often respond favorably to an applica- 

 tion of ground limestone. 



FUNCTION OF CARBONATES IN SOILS. 



The chief function of carbonates in the soil is the neutralizing of 

 acidity. In natural soil processes acids are produced from the decay- 

 ing of organic matter just as acid is formed in the souring of milk, in 

 the production of sauerkraut, in the fermenting of silage and in the 

 manufacture of wine and vinegar from fruit juices. Also by the 

 process of nitrification nitrogen in the organic matter of the soil is 

 converted into the strong mineral acid — nitric acid. It is important 

 to have in the soil at all times a material like limestone which will 

 keep these acids neutralized, but otherwise produce a neutral or only 

 faintly alkaline reaction. Lime carbonate also gives to soils a better 

 tilth by tending to produce a flocculated or crumb structure; while 

 acids have the effect of causing the soil to run together in a more 

 or less compact mass, which is just the opposite of tilth. Some soils 

 actually contain an insufficient amount of calcium and magnesium 

 for use as plant food, and in such cases limestone has the important 

 function of furnishing these elements in easily available form. Many 

 farm crops use an insignificant amount of calcium and magnesium 

 as plant food; but a few, notably clover and alfalfa, use them in 

 relatively large amounts. One ton of cured alfalfa hay contains 

 these elements in a total amount equivalent to as much as 100 pounds 

 of limestone. 



Nearly all farm crops are sensitive to an acid condition of the soil, 

 but clover, alfalfa, vetch, bluegrass, timothy, beets and others can 



