Lime and Calcium Compounds 141 



effects which are not limited to any one field. It affects 

 the soil itself, changes its texture and mechanical proper- 

 ties, such as its power of taking up and holding moisture. 

 It acts upon the supply of plant-food stored in the soil and 

 assists the decomposition of organic matter and mineral 

 substances. Most important of all is the influence which 

 lime exerts upon the microorganic life of the soil, so essen- 

 tial in changing dormant to active forms of plant-food. 

 Hence, the activities of lime in the soil may be said to 

 be threefold, mechanical, chemical and biological. 



Mechanical effects of lime. 



It is often stated that lime makes heavy soils lighter 

 and light soils heavier. This is the apparent effect rather 

 than the actual. Applications of lime upon heavy soils 

 make them less sticky, more crumbly, more friable, more 

 easily cultivated, and water passes through them more 

 rapidly as the result of increased porosity. This condition 

 is brought about by the flocculation or aggregation of the 

 fine clay particles preventing shrinkage in dry weather. 



Upon light soils the reverse is true. An application of 

 lime tends to increase the cohesive power of the soil, 

 resulting in a greater water-holding capacity, as well as 

 increasing the power to absorb moisture from below by 

 capillarity. Light, sandy soils may, however, be injured 

 by large applications of lime, especially if it is in the 

 caustic form which causes a greater porosity and allows 

 water to pass through too rapidly. Upon muck or peat 

 soils, lime should always be mixed with the surface soil. 

 A layer of lime spread over the surface of such soils has a 

 tendency to exhaust the organic matter, and injury may 

 follow especially in case of drouth because the water- 

 holding capacity is decreased. 



