CHAPTER XIII 



IMPROVING THE CHEMICAL NATURE 

 OF THE SOIL 



116. What Plants Remove from the Soil. The amount 

 of mineral food substances removed from the soil by a 

 bountiful harvest is considerable. The object of fertil- 

 izing is not only to return to the soil the elements that 

 help the growth of the crops, but also to improve the 

 tilth. In applying fertilizers, we should remember that 

 our effort is to bring about a twofold result: (a) to supply 

 mineral food, and (6) to improve the texture of the soil. 

 While, ordinarily, we add substances supplying soluble 

 salts containing nitrogen, potassium, and phosphorus, it 

 should be remembered that equally beneficial results are 

 sometimes secured by applying dressings of substances 

 that do not contain any considerable quantities of these 

 elements, as lime, plaster of Paris, or gypsum. The 

 benefits derived from these substances are due to the 

 effect they have on the physical properties of the soil. 

 The lime may also cause the decomposition of insoluble 

 particles containing potassium or phosphorus. (Fig. 45.) 



116a. Corn contains about 1.58 per cent of nitrogen; 0.37 per 

 cent of potassium; and 0.57 per cent of phosphorus. How much of 

 each does a crop of 50 bushels per acre remove from the soil? 



117. Not All Soils Need the Same Fertilizer. Experi- 

 ments have shown that the chemical analysis of a soil 

 does not give a farmer a satisfactory guide as to what 

 fertilizer to apply to his land. The analysis might show 

 a high per cent of potash, and yet it might be in such 



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