218 ANNUAL REPORT OF THE Off. D«c. 



and the crop what is needed,"' and they advocated what are called 

 fertilizer plol experiments. The plot of laud selected was divided 

 into several long narrow strips, one was fertilized with a complete 

 manure containing nitrogen, phosphoric acid and potash; a second 



with the same itting the nitrogen; a third omitting the phosphoric 



acid and a fourth omit ling the potash. It' the removal of any one 

 of the elements caused a decrease in the crop, it showed that the 

 soil was deficient in that element. Many combinations have been 

 tried in addition to those mentioned above and many hundreds of 

 these tests have been carried out in various parts of the United 

 States. Their value to agriculture has been almost nothing and for 

 these reasons. If the tests are successful the most they can tell 

 you is a year later than the information is needed, for the results 

 indicate what the field needed at the beginning of last season, but 

 not what it will need next season, after the present year's crop has 

 drawn its supplies of plant food from the soil. It may indicate 

 what is needed for the special crop grown but it does not show what 

 may or may not be needed by a crop of another kind on the same 

 soil; nor does it offer any solution to the problem of what is 

 needed in another county, on another farm or even on another field 

 of the same farm. 



Nearer a correct theory of farm fertilization were those who have 

 advocated the doctrine: "Add to the soil what you expect the crop 

 to take from the soil." But even this theory does not go quite far 

 enough. The fundamental objection to all the earlier theories is 

 that they were seeking some way by which the addition of a partial 

 fertilizer would produce a full crop. In other words, they sought 

 to add only part of the plant food needed and expected the crop to 

 obtain the remainder from the store of plant food already in the 

 soil. Such theories are not correct, for they violate the rule laid 

 down at the opening of this article. If such a scheme of fertili- 

 zation was carried on for a long term of years, it would eventually 

 impoverish the ground. . 



The correct doctrine is that one which instead of striving to see 

 how much of the needed fertilizer can be secured from the supplies 

 already in the soil, looks on all the plant food in the soil as so much 

 working capital, to be used as needed, but never to be reduced and 

 to be augmented continually for the production of better and larger 

 crops. 



The last theory mentioned is not quite correct, because all plants 

 need at their command a good deal more plant food than is to be 

 removed in the crop. Thus in the case of clover, a crop of two tons 

 to the acre removes about 80 pounds of potash per acre. Never- 

 theless the crop at the beginning of the season must have at its 

 disposal much more than this 80 pounds of potash, for the roots 



