SOILS AND FERTILIZERS 509 



be produced, which is supposed to be particularly noxious to most 

 agricultural plants, though apparently not detrimental to the growth 

 of the cranberry, watermelon, rhododendron, azalea, and a few other 

 herbaceous plants, trees, and shrubs. Such conditions are liable to 

 occur even in upland and naturally well-drained soils. Liming is in 

 all such cases an effectual and probably the most economical remedy. 



Physical Effects of Liming. Many clay soils when wet by 

 rains are not porous enough to allow the water to pass through them 

 with sufficient rapidity, in consequence of which they become water- 

 logged and the air which is necessary for the healthful development 

 of plant roots within the soil is excluded. In times of drought, also, 

 such soils cake readily, thus becoming more difficult to till and less 

 adapted physically to the growth of plants. Liming is an effective 

 preventive or remedy for all of these unfavorable conditions. Upon 

 certain loamy soils containing considerable clay, liming often ren- 

 ders the surface more friable and less liable to form a crust upon 

 drying. 



The improvement of drainage brought about by liming is one 

 of the most effective means of preventing surface washing. When 

 heavy rains occur on limed soils the water sinks into the soil instead 

 of rushing over the surface, carrying the fine soil particles with it 

 and thus producing galls and washes. Soils which are composed of 

 siliceous sand are frequently benefited by being rendered more com- 

 pact by liming. On such soils pulverized limestone is preferable to 

 ground burnt lime, hydrated lime, or even air-slaked lime, owing to 

 the more powerful action of the latter, and the best material to em- 

 ploy where it is obtainable is a clay marl containing a fair amount 

 of carbonate of lime. The clay, as well as the lime, tends to mate- 

 rially improve the physical condition of the soil. It should also be 

 the aim to increase the amount of organic matter in such soils by 

 the use of muck and stable manures, or by the occasional plowing 

 under of a green crop or of sward. 



Effect of Lime on the Action of Microscopic Organisms in the 

 Soil. Many important changes are produced in the soil by organ- 

 isms so small that they can only be observed by the aid of the most 

 powerful microscopes. Some of the changes of this character in 

 which lime plays an important part are the following: 



(1) The change of ammonia and of nitrogen in organic 

 matter, such as blood, meat, fish, tankage, plants, etc., into nitrates, 

 the form in which it is chiefly assimilated by most cultivated plants. 

 This is known as the process of nitrification and is promoted by the 

 presence of lime in soils. 



(2) The decomposition of organic matter in muck and other 

 soils. In this process the production of carbonic 'acid is much ac- 

 celerated by the use of lime. This carbonic acid in turn so acts 

 upon the inert plant food of the soil as to make it more quickly avail- 

 able to plants. The indirect result, therefore, is to help the plant 

 to draw more potash, phosphoric acid, etc., from the soil than 

 would otherwise be possible. 



