New York Agricultural Experiment Station. 57 



Some soils may contain larger quantities than these. But when 

 we consider the total amount of plant food in one acre of soil, the 

 amounts appear large. 



While the weight of soil in an acre of different kinds of land 



varies, we may take the average weight of dry soil in one acre to 



the depth of nine inches as approximating about 3,0ti0,000 to 



3,500,000 pounds. One acre of soil containing the proportions of 



plant-food given above would, therefore, contain the following 



aggregate amounts : 



Nitrogen, 4,500 lbs. 



Phosphoric Acid, 4,500 lbs. 



Potash, 6,(i00 lbs. 



A large portion of the plant-food in the soil is not available. The 

 character of the soil aiiects very considerably the available condition 

 of the plant-food. For example, a sandy soil is rendered fertile by 

 a smaller amount of plant-food than is a clay soil, owing, in part to 

 the greater development of roots in a sandy soil, and, in part, to the 

 different condition in which the mineral food exists in the sandy 

 soil. The insoluble condition of plant-food in the soil prevents its 

 rapid loss by leaching. 



Loss of Fertilizing Constituents from the Soil. — Without 

 going into a detailed explanation in regard to the causes, we will 

 consider briefly the extent to which the three chief forms of plant- 

 food are liable to be lost from soils. 



(a) Phosplioric Acid in Phosphates. — The ordinary form of 

 calcium phosphate being insoluble in water, is not, to any appre- 

 ciable extent, removed from the soil by the drainage water. The 

 soluable form of calcium phosphate would probably be lost to some 

 extent in drainage water, were it not for the fact that it is quickly 

 changed in the soil to the " reverted " or less soluble form and, in 

 this "reverted '' condition, the phosphate is not apt to be carried 

 away in drainage water. 



{])) Nitrogen Compounds. — Since ammonia compounds and 

 nitrates dissolve easily in water, is there not danger of their being 

 carried away in drainage water from the upper soil out of reach of 

 the plants? Experiments have been made to settle the question, 

 and results indicate that ammonia compounds are largely retained 

 in the soil. Nitrates are apt to he loashed out and lost in the case 

 of hare falloio land ; but, when the soil is covered with vegetation, 

 there is little or no loss, for the reason that the roots of growing 



