SOILS AND FERTILIZERS 445 



natural belief that the proper way to do this is by analyzing a sample 

 of the soil in question. This method would doubtless be satisfactory 

 if it were not for the fact that it is almost impossible to tell by 

 analysis how much of the plant food present is available. The total 

 amount of nitrogen, phosphorus, potassium and other plant food 

 materials can be ascertained by analysis, but as far the greater 

 part of this material cannot be secured by the plants, and the propor- 

 tion that can be obtained varies decidedly in different soils, and 

 with different crops, the determination of the total amount is of 

 rather uncertain value in showing the fertilizer requirements of a 

 soil. 



The beneficial effect of any fertilizer on a particular soil depends 

 on whether the fertilizer in question contains those elements of 

 plant food in suitable quantity and quality in which the soil is 

 deficient. In other words the supply of plant food in soils varies 

 widely and every user of commercial fertilizers must select his fer- 

 tilizer according to the conditions of his soil and the requirements of 

 the crop which he wishes to raise. The question is often asked which 

 is the best mixed fertilizer to use. The consumer can better answer 

 this question for himself by a study of his soil conditions and crop 

 requirements. A general statement may be made, however, to the 

 effect that, all conditions being equal, the consumer should select 

 those fertilizers which give the greatest amount of plant food in 

 suitable and available forms for the least money. 



The most satisfactory, and, indeed, usually the only method 

 by which one can at present determine the needs of a soil is to ask 

 the question of the soil itself by growing a crop upon it with different 

 kinds of fertilizers and noting the result. Such soil tests with fer- 

 tilizers have in many cases given results of much immediate prac- 

 tical value for the locality in which they were undertaken. As a 

 rule, however, farmers have looked upon such experiments as some- 

 thing too costly and complicated for them to undertake and con- 

 sequently they have perforce been content to use fertilizers in a more 

 or less haphazard manner, and in many cases, no doubt, at a great 

 financial disadvantage. 



The best method of ascertaining what is needed in any given 

 case to produce a particular crop is to put the question to the soil 

 itself; and this method, though requiring care at all points, and 

 caution in forming conclusions, is not in reality difficult. Such ex- 

 periments should abundantly repay the investigator in the practical 

 money value of the results. 



Law of the Minimum. Since so many conditions surround and 

 influence the growth of a plant it is important to find out which 

 ones affect the growth of the plant most. It has been found by ex- 

 perimentation that it is not the most favorable conditions but the 

 most 'unfavorable ones which have the greatest influence upon the 

 growth of a plant. There may be one hundred conditions favorable 

 for plant growth, and five or even one, only, which is unfavorable. 

 It is not the many favorable conditions but the few unfavorable ones 

 which influence the growth of the plant, or crop. 



