FERTILIZERS 131 



Manure, in addition to supplying the much-needed plant ele- 

 ments to the soil, improves the condition of the soil in many ways. 

 It binds together particles of sandy soil, makes dry soils more 

 mellow or porous, and conserves the soil moisture for the use of 

 plants. 



Composts are formed by building up alternate layers of manure 

 and of weeds, marl, leaves, etc. The various layers of material 

 are thoroughly moistened with water as they are built up. The 

 heap is finally rounded off into a cone-shaped pyramid and is 

 covered with a layer of dry soil to absorb and retain all gases that 

 are formed. Whenever possible the compost heap should be 

 opened up occasionally and sufficient water added to make the 

 whole mass thoroughly moist. This will check the destructive 

 fermentation and will facilitate the formation of nitrates. 



Commercial Fertilizers. When the soil is kept in constant 

 cultivation and the crops are sold year after year, the essential ele- 

 ments of plant food become exhausted, and frequently not enough 

 manure is produced on the farm to supply the deficiency; farmers 

 are then compelled to resort to special or commercial fertilizers. 

 These consist of compounds manufactured expressly for use on 

 soils, and they contain plant food in a form more highly concen- 

 trated and more readily available than that found in stable or 

 barnyard manure. 



Classes of Commercial Fertilizers. All special or commercial 

 fertilizers fall naturally into three classes: 



1. Nitrogenous fertilizers, or those furnishing nitrogen. 2. Po- 

 tassic fertilizers, or those furnishing potash. 3. Phosphatic fer- 

 tilizers, or those furnishing phosphorus. 



Hints on Fertilizers. A reckless and indiscriminate use of 

 fertilizers is never profitable. The farmer must know what ele- 

 ments are needed for the successful growth of a crop and the 

 amount that should be applied in each case. Good tillage, proper 

 rotation of crops, and a judicious use of natural manures or fer- 

 tilizers will ordinarily insure successful crops. But it is frequently 

 advisable to supplement the natural manures with concentrated 

 commercial fertilizers that have been found beneficial to that par- 

 ticular crop the farmer is trying to grow. 



Nitrogenous Fertilizers. Since nitrogen is the basis of the 



