320 SYSTEMS OF PERMANENT AGRICULTURE 



remembered that well-fed plants are usually better able to resist 

 or overcome the attacks of insects and diseases. It is well known 

 that there are some exudations from germinating seeds, and it 

 seems evident that water used repeatedly for 2O-day cultures with 

 'seedling plants becomes stagnant, putrid, or toxic, but can we 

 correlate this with field conditions? 



Alkaline slag phosphate, acidulated rock phosphate, neutral 

 steamed bone meal, and insoluble raw rock phosphate are very 

 different chemical substances, and the very complete data already 

 presented show that any one of these forms of phosphorus may be 

 used to increase crop yields. Sodium nitrate, ammonium sulfate, 

 and dried blood are exceedingly different substances, but they all 

 contain nitrogen, and where nitrogen is deficient in the soil, any 

 one of these materials will benefit the crop. Moreover, with legume 

 plants, essentially the same results are secured whether nitrogen is 

 supplied in dried blood or provided by the nitrogen-fixing bacteria 

 without fertilizer application. 



It may be noted that while Whitney and Cameron in Bulletin 22 

 (1903), of the Bureau of Soils, included nitrogen as distinctly as 

 phosphorus, potassium, and calcium, as being contained in prac- 

 tically all soils in an ample supply which " will be indefinitely 

 maintained," and while Professor Whitney also asserts, in Farmers' 

 Bulletin 257 (1906), that the correction of toxic substances is 

 " the principal office of nitrate of soda, potash, and phosphoric 

 acid," and while Cameron admits in the Hearings before the Com- 

 mittee on Agriculture (1908) that it is never necessary at any time 

 to introduce fertilizing material into any soil for the purpose of 

 increasing the amount of plant food in that soil; nevertheless, 

 Whitney and Cameron are beginning to qualify their theories by 

 saying " mineral elements " or " mineral plant food," presumably 

 because the mathematical opposition is too strong, considering 

 that the soil contains but very small amounts of nitrogen " far 

 below where the roots go." 



On December 9, 1908, the National Conservation Commission 

 presented its report (prepared for the President) to the Conference 

 of Governors and State Conservation Commissioners assembled 

 in Washington, in which great emphasis was laid upon the impor- 

 tance of conserving the supply of natural phosphates, as a result 



