CHAPTER XII 



LIMESTONE 



CALCIUM carbonate, in the form of chalk or marl, has been used 

 for soil improvement since the beginning of agricultural history. 

 Large use has been made of these natural materials in England and 

 France, especially. An English record of 1795 mentions the " pre- 

 vailing practice of sinking pits for the purpose of chalking the 

 surrounding land therefrom," and states that " the most experi- 

 enced Hertfordshire farmers agree that chalking of lands so circum- 

 stanced is the best mode of culture they are capable of receiving." 



On the famous Rothamsted Experiment Station it has been found 

 that the fields that had received liberal applications of this natural 

 limestone a century ago are still moderately productive, while 

 certain fields remote from the chalk pits which show no evidence 

 of such applications are extremely unproductive. Director Hall 

 of the Rothamsted Experiment Station states that many of the 

 farmers in that vicinity are still reaping profitable crops from 

 lands enriched by the heavy applications of chalk made by their 

 ancestors many years ago. 



There appears to be no record that these easily pulverized lime- 

 stone materials have ever been burned in order to increase their 

 agricultural value. The productive power and durability of the 

 natural limestone soils is indicated by the time-honored truth, 

 " A limestone country is a rich country." 



Where such natural materials as chalk and marl have not been 

 accessible, more or less use has been made of water-slacked or air- 

 slacked lime; because, by burning and slacking, limestone rock may 

 be reduced to powdered form and thus distributed over the land. 



With the development of rock-crushing and rock-grinding 

 machinery, fine-ground natural unburned limestone can be had, 

 and where this material can be gotten at reasonable cost, it 

 replaces all other forms of lime used for the improvement of nor- 

 mal soils. 



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