FOURTEENTH ANNUAL YEAR BOOK— PART X. 711 



tions, spend their entire time on such work, only a small part of the 

 samples annually received could be analyzed. Therefore such analyses 

 are out of the question for financial reasons. 



But there are further and more important reasons why such analyses 

 are not made. In the first place, samples of soil taken at random 

 without regard to their representative character may be so very local 

 in nature that their analyses would be of practically no use to the 

 farmer, and of absolutely no general value. Furthermore, complete 

 chemical analyses of soils give only their total plant food content. Such 

 analyses may show lack of nitrogen, phosphorous or potassium, or an 

 abundance of these elements, but they give no idea of the rate at which 

 they become available, and hence merely indicate the ability of the 

 soil to support plant growth. For instance, nitrogen, phosphorous and 

 potassium may be shown by chemical analyses to be present in abun- 

 dant amounts, but an application of a nitrogenous, as phosphate, or a 

 potassic fertilizer might yield astonishing returns. On the other hand, 

 very small amounts of these constituents might be present and yet 

 additional applications might give a very small, or even no increase 

 and therefore represent an actual money loss. 



The reason for this is simple. All plant food in the soil does not 

 exist in a form available for plants. That is, it must be prepared for 

 them just as human food is prepared in kitchens. The raw materials 

 are acted upon by various agencies and changed into forms which are 

 of use to plants. The bacteria may be called the cooks in charge of 

 the plant kitchens. When these cooks are inefficient there is a decrease 

 in the production of. prepared food and the plants are inadequately fed. 

 When the cooks go out on a strike, because of improper working con- 

 ditions, such as lack of air, water, or food (organic matter), no food 

 is prepared and the plants starve. 



In all soils there is a certain relation between the raw food known 

 as potential, or total plant food, and the prepared material, known as 

 active or available plant food, and this relation is determined by the 

 efficiency of the bacteria (the cooks). That efficiency is secured by keep- 

 ing conditions in soils satisfactory for bacterial growth by providing 

 the proper amount of air, maintaining the best moisture conditions, and 

 supplying food material, or organic matter. These conditions may be 

 kept right by proper tillage, drainage or irrigation, and the addition 

 of manure. 



Chemical analyses do not show whether or not conditions are right 

 for bacterial activity. Chemical analyses, as has been pointed out, 

 give only the total or potential plant food content of soils and hence 

 merely indicate the needs of the soil, unless the total food supply is 

 very small, in which case it is safe to assume that more should be 

 added. 



It has been well said that "the chief value of a chemical analysis is 

 to serve as an absolute foundation upon which methods of soil treat- 

 ment can be safely based for the adoption of systems of permanent soil 

 enrichment, not for one crop or one year, but for progressive improve- 

 ment." 



