REPORT OF THE SECRETAEV. 153 



the effect left by these crops which influences succeeding crops, and 

 that for the highest development of the soil crops must succeea crops 

 in a certain general order, which order of rotation is dependent upon 

 the nature of the soil as well as upon climatic conditions and cultural 

 treatment. 



COMMERCIAL FERTILIZERS. 



The subject of the use of commercial fertilizers, which has de- 

 veloped to so large proportions in the last 50 years, has also been 

 investigated by the bureau, and it has been found that tliey have 

 very important functions in addition to their value as mineral plant 

 foods. 



The soil is not static, as was formerly supposed, but is dynamic, 

 with many functions continually at work producing changes and 

 always mutually atfecting one another, and these changes can also 

 be profoundly influenced by the substances ordinarily used as soil 

 amendments. 



It has further been shown that the United States has within its 

 borders ample supplies of the raw materials which experience has 

 proved to be most useful as fertilizers to supply the Nation's needs 

 for an indefinite period into the future. 



There is in this country enough high-grade phosphate rock to sup- 

 ply three times the present demands for 12 centuries or more. The 

 giant kelps of the Pacific coast and Alaska, if properly conserved 

 and cropped on scientific principles, can probably surpass in yield of 

 potash salts the famous Stassfurt mines, and there is reason to 

 expect that commercial production of potash from feldspar will 

 soon be a reality. With many sources of nitrogen carriers yet to be 

 utilized to their fullest extent and with practicable methods of 

 " fixing " atmospheric nitrogen already finding a home in this coun- 

 try, the future may be faced with equanimity so far as problems of 

 supply are concerned. 



All of the results of fertilizer experiments that have been made 

 and published in this country have been summarized in a series of 

 bulletins, which, together with the laboratory investigations now 

 going on, will ultimately, it is believed, lay the foundation for a 

 rational system of fertilization. 



FUTURE PRODUCTIVITY. 



With intelligence and care in the cultivation of the lands already 

 under agricultural occupation and in the taking up of idle lands 

 with increasing density of population, it is estimated that the soils 

 of this country will be in about the same state of development as the 

 soils of France and Germany, and that they will produce many times 

 as much as they do to-day. 



