SOIL IMPROVEMENT 83 



nature ; when they have, they do not retain it unless they are prop- 

 erly cultivated. 



Improving Soils. The farmer cannot change the character of 

 a soil, but he can modify and improve it. There are three ways 

 in which soils need to b2 cared for and improved. 



Texture. First : The texture should b3 attended to, so as to give 

 plants the bsst possible conditions with regard to moisture, air, 

 and heat. This is done by proper tillage and by applications of 

 manures which supply humus. Humus is lacking in most of the 

 ' run down ' farms of the East ; it is abundant in the fertile prairie 

 lands of the West. Lime, too, often benefits the texture and con- 

 dition of land. 



Plant Food. Second : There should be supplied the plant food 

 which is naturally lacking, or which is taken out by crops. You 

 know that there are three elements that sometimes need to be 

 supplied, and that they must be in forms which plants can use. 

 Nitrogen is used chiefly in the form of nitrates; phosphorus, of 

 phos phor'ic acid; and potassium, of potash: all three are com- 

 pounds formed -with oxygen. 



All crops do not remove elements in the same amounts or the 

 same proportions. Forage crops, for instance, of which the stems 

 and leaves are used, need much nitrogen to form their luxuriant 

 foliage; grain crops store up much phosphorus in their seeds. 

 Legumes are sometimes called ' lime plants ' because they use 

 so much calcium, which is usually applied to the soil in the form 

 of lime. Whatever is taken from the land must have its place 

 supplied, or the land grows poor. 



Conditions for Bacteria. Third: Conditions should be made 

 favorable for nitrogen-gathering bacteria. You have already 

 learned that these tiny creatures in the soil change nitrogen into 

 compounds which plants can use. These bacteria will not work 



