ESSENTIAL FERTILIZERS 15 



turned under, to decay. Excessive evaporation can be 

 prevented by shallow cultivation after a crop has been 

 planted. After a shallow cultivation the fine soil on top 

 dries out quickly ; and in a loose, dry condition it acts as 

 a barrier to the upward movement of the capillary water 

 beneath. Thus this layer of fine, dry soil, which is called 

 a soil mulch, acts as a blanket to prevent evaporation. 

 When a soil mulch becomes compacted by a rain it no 

 longer acts as a barrier to capillary water and excessive 

 evaporation begins anew. The ground should be given a 

 shallow cultivation after each rain in order to form a new 

 mulch. 



Essential Fertilizers. The elements needed by plants 

 are found in the soil in sufficient quantity with but three 

 exceptions, nitrogen, potassium, and phosphorus. These 

 exist in the soil in very small amounts, and if plants are 

 continually grown thereon and removed, these substances 

 soon become exhausted. They must be supplied to the 

 land by some means if good crops are to be secured. Barn- 

 yard manure is called a complete fertilizer because it con- 

 tains all of these three elements. It is ordinarily the best 

 fertilizer to use when it can be obtained. Nitrogen is 

 furnished by legumes. Other important sources of nitrogen 

 are cottonseed meal and nitrate of soda. Muriate of 

 potash is one of the potassium fertilizers. Bone meal and 

 rock phosphate are added to furnish phosphorus to the 

 soil. 



Lime is used as a fertilizer on some soils, but more often 

 it is used to sweeten sour soils. An acid, or sour, condi- 

 tion of the soil is unfavorable to crops, and therefore this 

 action of lime in destroying soil acidity is extremely im- 

 portant to the farmer. 



