236 THE MONTHLY BULLETIN. 



crop, which is a totally different matter from that here under con- 

 sideration, will depend upon the supply of those essentials above 

 considered, without which there can be no successful plant growth. 



ANALYSIS OF A SOIL AS A CRITERION TO FERTILIZER NEEDS. 



No less tenaciously held than the foregoing misconceptions is that 

 with respect to the indication of fertilizer needs by chemical analysis 

 of soils. This idea comes down to us from the days of Liebig, who 

 with many others believed that analysis of soils and analysis of plants 

 by prevalent methods would, by giving us a cue to amounts of minerals 

 found in soils and in plants respectively, indicate what minerals and 

 in what quantities they should be returned to the soil to maintain 

 fertility'. While this kind of an idea appears logical enough, super- 

 ficially, more careful reflection and numerous experiments prove it to 

 be, if not erroneous, at least of little practical value. To be sure, in 

 soils which are totally deficient in plant foods, like the leached sands 

 and peats of the Atlantic coast and elsewhere, chemical analyses indi- 

 cate in general that fertilizer applications are necessary. But in the 

 large number of soils which do not belong to that class, and especially 

 in those deep soils of this State which are so well supplied with large 

 quantities of the plant food elements, ordinary chemical analysis of 

 soils can not be used as a criterion to fertilizer needs. 



When I speak of analysis in connection with this subject I mean, of 

 course, complete chemical analysis of soil, either by the strong acid 

 digestion method or by the fusion method. 



The reason for the remarks above made is that in the first place the 

 methods described do not show amounts of available plant food; that, 

 secondly, plants take up relatively small quantities of minerals from 

 the soil; that, thirdly, the largest portion of their weight by far consists 

 of carbon, hydrogen and oxygen, which come from the air and from 

 M^ater ; that, fourthly, there are many soils which do not contain enough 

 plant food, as shown by the methods of analysis above named and their 

 standards of interpretation, which nevertheless produce good crops, 

 provided the plant food they contain is made available. 



This remark is particularly cogent in connection with the deep soils 

 of this State, which offer so large a surface to root development as to 

 make up for lack of plant food and sometimes even for a lack of avail- 

 able plant food. By available plant food we mean, of course, that wliich 

 is soluble in soil water and we are powerless, by the method of chemical 

 analysis above referred to, to tell if the plant food is in available form. 

 There are methods of analysis which are of some little value in that 

 direction, but they are not the methods ordinarily carried out, and 

 consist of extracting soils with water or with weak citric acid, or with 

 carbonated water. These solvents, which are presumed to be much 

 like the soil water in solvent effects, do give some indication, as careful 

 experiment shows, of the extent to which plant food is available in any 

 given soil. There is no doubt that these methods will be used more 

 largely in the future or, at least, that methods like them will be used 

 more "largely, where chemical laboratory work is at all called in as a 

 guide to fertilizer needs of soils. 



Moreover, there are other objections than those above named to the 

 validity of complete chemical analyses of soils as criteria to their ferti- 



