aspects that their solution can be arrived at only through much study and experiment. 

 To state in a general way what profit, if any, will result from their use is not possible. 

 Fertilizers may be and are used profitably in many instances. On the other hand, 

 their indiscriminate purchase and use is almost sure to result in general loss. 



Experimentation, so far as it has gone, has led to some definite conclusions: 



First : Commercial fertilizers are not a substitute for manure, and it is not possible 

 to maintain soil fertility by their use alone. To attempt it is not sound practice, either 

 scientifically or economically. They are supplements to manure, not substitutes for it. 



Second: In the larger number of instances, where profit has been obtained, it has 

 resulted from the application of a "complete" fertilizer. A compound in which the 

 three elements, nitrogen, phosphoric acid and potash are present is known as a "com- 

 plete" fertilizer. 



Third: The largest profits do not always result from the largest application. 

 Farmers sometimes reason that, if a certain amount of fertilizer is good, more is better. 

 Not at all. That is not the way to look at it. The point to observe is not so much 

 increased yield as increased profit. The increase in yield between the use of 300 

 pounds and 500 pounds of fertilizer may not be sufficient to justify the increase in 

 cost. Speaking generally, the best returns, dollar for dollar, have been obtained from 

 moderate applications. 



Fourth: It is a known fact that the growth of crops is limited by the percentage 

 of plant food that is present in the minimum. If, for instance, there is an excess of 

 available nitrogen and an excess of potash, but only a small amount of phosphoric 

 acid — not sufficient for the needs of the crop — the amount of phosphoric acid will 

 determine results. In this fact will probably be found the chief reason why in the 

 majority of instances a complete fertilizer is desirable. There are occasions, doubtless, 

 where the special requirements of a crop or the deficiencies of the soil call for special 

 applications of one or more of these elements. A knowledge of such facts forms the 

 basis for the economic compounding of a fertilizer. 



Many assume that a chemical analysis of soil and crop should determine require- 

 ments. The complete analysis of a soil is seldom to be justified for this reason: The 

 immediately available elements in a soil mark its fertility. As, invariably, the immedi- 

 ately available elements are present only in very small amounts, it is not easy to dis- 

 tinguish by analysis between the available and non-available. Nor is it possible to 

 predict by this means the return obtainable from any particular fertilizer. There are, 

 however, one or two chemical tests that enable advice to be given in a general way as 

 to soil deficiencies, with the probability that profit will result from supplying the 

 elements that are lacking. We must appeal to the soil itself by actual tests with 

 fertilizers. Perhaps the best way for the farmer to do this is to leave a strip undressed 

 with fertilizer for comparison; but it should be borne in mind that the full result is 

 not always seen in the first crop that follows the application. 



INOCULATION OF LEGUMES 



One of the chief benefits from growing legumes is the nitrogen left in the soil by 

 the decay of the root tubercules or nodules. Every legume in order to have tubercules 

 on its roots must be inoculated with the specific organism that has been isolated from 

 that particular legume, or with soil in which nodulated plants of that legume have 

 been successfully grown. Repeated trials have shown that under ordinary farm con- 

 ditions bacteria that form nodules on one legume will not produce nodules on legumes 

 of any other species. The bacteria left in the soil by the red clover nodules will not 

 provide inoculation for a successful crop of alfalfa nor vice versa. There is one notable 

 exception to this rule: Cross-inoculation is possible between alfalfa and sweet clover. 

 The strain of bacteria that produce nodules upon sweet clover will also produce nodules 

 upon the alfalfa plant, but this is the only practical example of the kind. 



73 



