FERTILIZERS. 31 



mineral elements contained in the soil and rocks, that are rendered soluble through the 

 agencies of the atmosphere, water, heat, and cold all these, though silent and gradual in 

 their working, affect the productiveness of soils in a remarkable degree. The washing of the 

 fertilizing properties from the mountains and hills is one great reason why the valleys contain 

 usually the most productive soils. 



The food of plants is derived from two sources, viz., the soil and atmosphere. The 

 elements obtained from these two sources, though greatly varying in proportionate quantities, 

 are equally essential, as far as the plant-growth is concerned, and no excess in the amount 

 furnished from one source can make up or counterbalance the deficiency in the quantity 

 furnished from the other, both being equally necessary. 



Elements of Plant-Food. The elements of plant-food necessary to produce plant- 

 growth are called organic and inorganic elements, and, in a general sense, embrace every 

 material which, if added to the soil, will tend to increase its fertility. Organic elements 

 embrace animal and vegetable substances which have a certain proportion of nitrogen ; 

 inorganic elements comprise those that are purely mineral or earthy, and which generally 

 contain no nitrogen. The organic elements, to be in the proper proportion, should be about 

 ninety-five per cent., the inorganic the remaining five per cent. By burning a plant, the 

 organic elements will be converted into gases, while the inorganic elements remain in the 

 form of ashes, called in analysis the ash of plants ; thus the organic element, or the ninety- 

 five pounds out of every one hundred pounds of the dried plant that is burned, and which is 

 derived mainly from the air, disappears, while the inorganic, or the five pounds out of every 

 one hundred pounds that are left behind in the form of ashes, are obtained from the soil. 

 Different plants differ somewhat in the proportion of the organic and inorganic elements 

 contained in them. The tobacco plant, for instance, having a larger proportion of ash than 

 many others, but, on the average, every plant that grows will have about ninety-five per cent, 

 of organic matter and five per cent, of inorganic matter, the organic matter being furnished 

 by the air, the inorganic by the soil. This, in the main, is the unchangeable law of nature. 



Since the atmospheric elements are found present in the soil, in a greater or less degree, 

 according to its texture and degree of porosity, it has been estimated that about one-half of 

 the material furnished to plants is derived from the earth. It was formerly believed that 

 plants depended for their nutrition upon the organic matter (or what is called humus) in the 

 soil. This humus theory was set aside by chemistry, which proved that certain soils were 

 extremely fertile with but two or three per cent, of humus in their composition, while certain 

 other soils were sterile with from twenty to forty per cent, of humus contained in them. 

 Afterward it was advocated by even the noted Liebig, that plants for nutrition required only 

 the application of the mineral elements. This theory was met by the nitrogen theory, 

 between which two (the mineral and nitrogen theories) a long contest ensued, until it was 

 discovered that in some respects both theories were right, and in others that both were 

 wrong. Then followed the theory, that in order to ascertain the wants of plants and provide 

 them with proper nutriment, we had only to analyze the soil and determine its wants, also 

 the structure and composition of plants, and by supplying the soil with the elements necessary 

 to certain plants, and in which it was deficient, a perfect supply of nutriment would thus be 

 furnished the plant. Although this theory seemed to approximate nearer the truth than 

 either of the preceding ones, still it had its objections, and its advocates were disappointed in 

 not meeting with that success in its practical application that had been anticipated ; for it 

 was soon found that the acids of the chemist, in analysis, would take from the sample of soil 

 certain elements which the plant never could find and appropriate from the soil, owing to its 

 being in such a state that it rendered it impossible to extract it from the soil. For instance, 

 the analysis of the soil might prove an abundant supply of phosphoric acid contained within 



it, but it might not be in such a solvent state as is necessary for the tender roots- to derive 

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