146 



CALIFORNIA FRUITS: HOW TO GROW THEM 



the writer's laboratory, which proved that lime and gypsum have 

 very different effects on different soils, depending on the kinds of 

 minerals and other substances which are contained in the soil origi- 

 nally. The addition of calcium in the form of lime increased the 

 amount of calcium in some soils, but not in others. This disposes 

 of the belief so tenaciously held by nearly all, soil and fertilizer 

 experts included, that the chief and only function of a fertilizer 

 consists in its furnishing a certain one or more plant food elements 

 which it contains to the soil solution. We can never really be certain 

 when we apply any fertilizer element to a soil that we enrich the 

 solution of that soil with respect to that element. That may occur 

 in many soils, but may not occur in many others. On the other hand, 

 it is likewise true that when a fertilizer element applied to a soil does 

 not enrich the soil solution with respect to itself, it may do so with 

 respect to another element theretofore insoluble. For example, we 

 may apply sulphate of potash to a soil without enriching the soil 

 solution there with respect to potash, but we may enrich it with 

 respect to calcium, magnesium, sodium or some other element which 

 may or may not be needed by the plant. While all this is true, how- 

 ever, the reader will doubtless readily grasp the significance of the 

 general situation, which may briefly be put in another way for 

 emphasis. If fertilizers carrying essential elements to plant growth 

 when applied to soils do not necessarily furnish those essential ele- 

 ments to the soil solution and still benefit the crop, the improvement 

 may be due to the increased supply, through the agency of the fertil- 

 izer, of some other element not necessarily essential, or an essential 

 element heretofore regarded as of minor importance which stimu- 

 lates the plant, not because it furnishes a lacking element, but be- 

 cause it causes increased cell growth in some other manner not now 

 understood by us. This may mean that we shall be able to use many 

 cheap salts or minerals for fertilizers to set free the essential ele- 

 ments already contained in the soil minerals or to stimulate plant 

 growth otherwise. Certainly, it may mean that in many soils we 

 shall be able to obtain an ample supply of soluble potassium in the 

 soil by applying, not potash fertilizers, but some substance which 

 does not contain potash, but which will set it free from its combina- 

 tions in the insoluble soil minerals. The reader will readily see that 

 this situation may effect profoundly the economics of the fertilizer 

 situation. The question that naturally arises next is how to de- 

 termine in practice the proper procedure in soil treatment by fertil- 

 izers. This will be taken up in detail in a special section below, after 

 a few other essential matters have been discussed. 



THE "SPECIFIC" EFFECTS OF THE ESSENTIAL 

 ELEMENTS ON PLANTS 



The text books on soils and those on plant physiology teach, so 

 far as I know, with a rare exception or two, that the so-called plant 

 food elements of fertilizers nitrogen, phosphorus, and potassium- 

 are not merely essential to plant growth but that each produces a 

 specific effect on the plant which is outwardly visible. For example, 



