FERTILIZERS 57 



HUMUS FERTILIZERS-NECESSITY OF 

 ORGANIC MATTER. 



86. Humus is decayed organic matter. It is neces- 

 sary for fertility, because all the nitrogen in soils 

 comes from either an animal or vegetable source. 

 (Very minute quantities are absorbed from the air 

 as ammonia and as nitrogen). The nitrates come 

 from humus. They are water soluble and can be 

 taken up by the roots. Thus the plant gets its 

 nitrogen. (15) (29) 



All fertile soils are rich in organic matter. The ex- 

 ceeding richness of new lands is due to the humus 

 deposited by succeeding crops for generations. This 

 is true of both the high mesa and the valley land. 

 It is possible to use some chemical form of nitrogen 

 and raise a plant, but it is expensive, requires close 

 watching and is not practical. The nitrogen from 

 organic fertilizers is yielded to the plant gradually, 

 with greater certainty, and is more lasting. 



87. Organic manures, whether of blood and bone, 

 or stable manure, or green cover crops, not only 

 furnish nitrogen to plant life, but their decay gen- 

 erates several well known acids, notably carbonic, 

 which combine with the soil moisture and dissolve 

 other forms of plant food. Without these acids, 

 phosphorus, potash and other necessary elements 

 would not be so available to the plant. Direct root 

 and water action would then have to do the work 

 alone, and the plant would not thrive so well. Hu- 

 mus influences the availability of the phosphoric 

 acid and potash and converts them into forms more 

 readily utilized by the plant. (49-50). 



