CHAPTER XIV 

 LIME 



In the chapter on acid soils, reference was made to lime 

 as a corrective of acidity. Lime is not a fertilizer in the 

 same sense as are the substances that have been discussed 

 in the last three chapters. It is, to be sure, an indispensable 

 ingredient of plant tissue, but as it is generally present in 

 sufficient quantity in arable soils, and as it is rather soluble, 

 there is usually enough lime to fully supply plant growth, and 

 this in spite of the fact that the soil may be greatly in need 

 of liming. It is because of its effect on the soil, rather than 

 directly on the plant, that lime is used as a soil amendment. 



241. Forms of lime. — The forms in which lime is used 

 on soils are (1) ground limestone, (2) marl, (3) air-slaked 

 lime, (4) quick-lime and (5) water-slaked lime. The first 

 three of these are similar in their effects, and are chemically 

 alike, being what is termed carbonate of lime. Quick-lime 

 and water-slaked lime have much the same action on soils, 

 and are called caustic lime. 



Quick-lime is made by burning limestone in a kiln. Quick- 

 lime, when treated with water, forms water-slaked lime. 

 Air-slaked lime is quick-lime that has been exposed to dry 

 air until it has lost its caustic properties. Marl is found in 

 beds in the earth, as is limestone, but it is softer than lime- 

 stone. Like limestone it is ground before being used. 



Owing to the combinations of the lime itself with water 

 and gases in these various forms, there is required a greater 

 weight of some forms than of others to give the same quantity 



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