380 MISCELLANEOUS FARM SUBJECTS 



In maintaining the fertility of the soil it is necessary to return 

 to the soil, in some measure, the elements of plant food removed 

 annually by the crops. The table on preceding page shows the ap- 

 proximate comparative fertilizing value of manure, rough feeds and 

 commercial fertilizing materials. 



RELATION OP CHEMISTRY TO CROP PRODUCTION. 



The investigations made by the Bureau of Soils during the last 

 ten years have shown that the economic distribution of crops is 

 dependent mainly upon the physical characteristics of soils and 

 upon climate. It has been believed that the chemical characteristics 

 of soils have a more or less direct and controlling influence on the 

 yield of a crop on any particular soil ; that is to say, where wheat 

 yielded 10 bushels per acre in one field, and in an adjoining field 

 (the soil of which had the same texture, so far as could be deter- 

 mined, although it might be in a better physical condition) 25 

 or 30 bushels were obtained, this difference in yield would be found 

 to be due to or associated with a difference in the amount of avail- 

 able plant food in the soil of the two fields. It was believed, further, 

 that the better physical condition resulting through loosening up 

 and aerating the soil and exposing it to the weathering influence 

 of the atmosphere by better and more thorough methods of cul- 

 tivation would in itself prepare a larger amount of readily avail- 

 able food material for the use of crops. 



These two subjects, distribution and yield, are both of vital 

 importance to the farmer; but while the yield of crops has been a 

 study for the experimenter and farmer alike throughout historic 

 times, too little attention has been paid by him to the adaptation 

 of particular soils to crops. The yield is today the paramount 

 question with the farmer, and all his energy and resources in the last 

 analysis tend to this end. 



The third object mentioned above, the control of the quality 

 of the crop, while beginning to receive more attention in general 

 agriculture, is a subject which has been of importance up to the 

 present only in special lines of agriculture, such, for example, as 

 the production of the different grades of tobacco. It has been given 

 particular attention by the horticulturist in improving the flavor 

 and coloring of fruits and has been studied in the highly developed 

 industry of floriculture in attempts to control the color, perfume, 

 shape, time of maturity, or other desirable quality of flowers. In 

 such specialized agricultural and horticultural industries, where 

 fertilizers are used to control the quality of crops, it is always con- 

 sidered a necessary prerequisite that the soil be put in the most per- 

 fect physical condition for the crop. The assumption that the soil 

 is in such perfect physical condition in general field culture can 

 never be safely made. 



Plants can and do yield ordinary crops, though growing in 

 media containing very small traces of all 01 the plant foods, while 

 if the amount of these plant foods is increased a thousand times, 

 as in the case of the alkali soils of the West, where potash, lime, 

 phosphoric acid, and nitrates are frequently found in very large 



