CHAPTER VII 

 PLANT-FOOD MATERIALS IN SOILS 



Plants secure their mineral food materials exclusively 

 from the soil. In a state of nature plants at death fall 

 on the surface of the ground and as decay proceeds, their 

 ash constituents return to the soil. The loss of mineral 

 matter, under these conditions, is due almost entirely to 

 its solution and removal in drainage water, or to erosion. 

 Under ordinary farm practice the procedure is different. 

 The aboveground portions of plants are removed wholly, 

 or in part, from the land and the loss of easily soluble min- 

 eral matter is thus greatly increased. The soil supply of 

 those particular elements required for the growth of crops 

 is a matter of great importance, for it is upon this that man 

 must depend for his sustenance, and although he may 

 supplement these elements in the soil by the use of manures, 

 the cost of food is thereby materially increased. 



105. Variations in content of plant nutrients in different 

 soils. — There are wide differences in the quantities of plant- 

 food materials in soils from different localities, although 

 the localities may be near together. This is illustrated by 

 the following statement of the analyses of soils from different 

 parts of the country, the number of pounds of each ingredi- 

 ent being based on the weight of 2,000,000 pounds of soil, 

 which is about the weight of the furrow slice of an acre of 

 land. 



90 



