108 A YEAR IN AGRICULTURE 



in the soil, large amounts of nitrogen will be supplied to the 

 soil. In addition to this value, the mass of material making 

 up the legume crop will add to the organic matter of the soil 

 and give all the values ascribed above. 



Organic matter and its relation to soil fertility. When 

 barnyard manures, crop residues, legume crops, or any other 

 organic matter are incorporated in the soil and the physical 

 conditions are right, the decay of this organic matter lib- 

 erates directly plant-food elements, helps to dissolve certain 

 mineral elements such as phosphorus and potassium, and 

 makes them available as plant-food. The organic content 

 of the soil provides a more suitable home for the growth of 

 bacteria, which are important factors in soil fertility. 



It must be noted in this connection that barnyard manure, 

 in addition to furnishing excellent organic matter, is also a 

 source of plant-food. Ordinary barnyard manure contains 

 per ton 10 pounds of nitrogen, 2 of phosphorus, 8 of potas- 

 sium, with a value of $2.22 per ton for the plant-food ele- 

 ments. We may see from these figures that it would take a 

 very great amount of barnyard manure to maintain per- 

 manently the fertility of the soil under maximum crop 

 production, as is also shown in the paragraph above on 

 plant-food required for crop growth. 



Nitrogen. Nitrogen is one of the most abundant elements 

 in nature, yet it is the most costly element to the farmer as 

 a plant-food. Some important facts regarding nitrogen em- 

 phasize its value to the farmer: 



a. All growing plants require nitrogen. 



