SOILS FERTILIZERS. 621 



above ratio, will be able to measure approximately, before tbe annual crop 

 sowin.ir, the quantities of manui'e which he must still apply to his land. In 

 doing this, however, he must take into consideration the average coetlicients of 

 utilization of the said plant foods and all the other factors which influence the 

 productive capacity of the soil." 



It is recognized that while these suggestions may be extremely helpful, " there 

 exists at present no method at once rapid and entirely free from objection, of 

 determining the manurial requirements — not the plant food requirements — of a 

 soil, and there is not likely to be one until the biological and colloido-chemical 

 actions taking place in the soil have been more clearly defined." 



In dealing with questions of fertilizing it is useful to keep in mind the law of 

 minimum as defined by liebig, or the law of physiological relations as defined 

 by Maz6 and Mitscherlich, and here it must also be borne in mind " that cer- 

 tain factors formerljr regarded as being present in excess, for example, carbonic 

 acid, are now suspected of being present only in the minimum quantity." Ac- 

 count must be taken of the variation in assimilating ix:)wer of different plants, 

 as explained in Strakosch's " law of the variation of work done by plants " 

 and in his idea of assimilative effect (E. S. R., 30, p. 332). 



As shown by Schulze and von Seelhorst, with the roots and stubble or even 

 the whole plant of leguminous crops turned under, the soil can not be depended 

 upon to produce maximum crops. Only about 30 per cent of the nitrogen of 

 green manures has been shown by von Seelhorst (E. S. R., 80, p. 24) to be 

 utilized by a three-course rotation. 



To get the best results solid and liquid manures should be stored separately. 

 " The liquid manure should be kept from contact with the air in a tank with 

 a lid, and should also be covered with a layer of petroleum or oil." 



Experiments which have been carried on for TO years on a farm at Wingen- 

 dorf near Freiberg, Saxony, seem to show that complete replacement of farm 

 manures by commercial fertilizers " can not be continued through several 

 decades without fundamentally impairing the yield, except on good soils con- 

 taining plenty of humus, and even then, only when the remains of the roots 

 and stubble are allowed to accumulate for the enrichment of the soil." How- 

 ever, it is shown that the great increase in the systematic and scientific use of 

 fertilizei's in Germany has been accompanied by a corresponding increase in 

 crop yields. 



In the author's opinion " the quintessence of human art in agriculture lies 

 ... in the correct application of fertilizers to well prepared soil, and in sowing 

 productive varieties." 



Some facts about commercial fertilizers in New York State, L. L. Van 

 Slyke (New York i^tate Sta. Bid. 392 (1014), PP- 585-625) .—This bulletin (1) 

 calls attention to differences in cost of plant food in commercial fertilizers sold 

 in New York, with suggestions as to the more economical purchase of such 

 plant food, (2) discusses the relation of guarantied to actual composition, and 

 (3) shows that the present state fertilizer law " needs amendment in order 

 to limit more carefully the amounts of deficiencies that are absolutely exempt." 



It is shown among other things that " the tendency among farmers at the 

 present time appears to be in the direction of purchasing more high-grade 

 mixtures, [but that] in complete fertilizers as well as in other mixtures and 

 unmixed materials, the variation in .celling price is often wholly out of pro- 

 portion to the amount of plant food present. . . . Plant foo<ls can be pur- 

 chased generally in unmixed materials at less cost than in mixtures." 



The analyses of fertilizers sold in the State in 1014 show that " in the case of 

 each constituent of complete fertilizers, the number of samples showing results 



