58 FERTILIZERS 



88. Organic fertilizers lighten soils. Their decay 

 leaves the soil open and porous. More oxygen is 

 thus admitted, which gives more life to the micro- 

 organisms, which, after all, are the cause of all fer- 

 tility. Better cultivation is possible in such soils. 

 Light, porous soils are more retentive of moisture. 

 Thus, organic matter literally builds up a soil. It 

 increases its depth. A "worn-out" soil is simply a 

 soil devoid of humus. It is lifeless. Liberal applica- 

 tions of organic matter restore it and change it from 

 a tax to an income. 



89. Humus forming-materials are, therefore, 

 necessary to successful and practical farming. The 

 best results from inorganic fertilizers, such as rock 

 and acid phosphates, Thomas slag and sulphate of 

 potash, are obtained when they are used with ma- 

 nure, or blood, or blood and bone, or a green cover 

 crop turned under. 



90. "Humus is not only the principal source of 

 nitrogen in soils, but it influences to a marked ex- 

 tent the available potash and phosphoric acid. 

 Humus forming materials, like green manures and 

 yard manure, have the power, when they decompose 

 in the soil, of combining with the potash and phos- 

 phoric acid of the soil and thus converting them into 

 forms which are readily utilized by the plants. "(82). 



CULTIVATION AND FERTILIZERS. 



91. Cultivation increases the availability of fer- 

 tilizers by aiding nitrification and by saving soil 

 moisture. All organic forms must first decay and 

 then be turned into nitrates (nitrification), and 



