148 



CALIFORNIA FRUITS: HOW TO GROW THEM 



a deficiency of a given mineral element may induce. For example, 

 it is pretty well established now that it is necessary not only to have 

 the nutrient solution of a plant of a certain concentration but also 

 that there be a proper balance among the various constituents there- 

 of. It is clear, therefore, that a plant may show an unthrifty con- 

 dition, due to too low a concentration of its nutrient medium or to 

 an improper balance of the different elements, without giving us 

 leave to correlate the unthrifty condition with a specific effect of a 

 given element. To put it another way, for emphasis, we may assume 

 that a plant will show a stunted condition or an abnormal color 

 which will be removed and the plant brought to a normal condition 

 by the application, let us say, of phosphorus or of potassium. This 

 does not argue that a deficiency of the element applied specifically 

 and characteristically causes the abnormal condition in question, but 

 may merely mean that a deficiency of any element by bringing about 

 an unbalanced condition in the nutrient solution may induce ab- 

 normal growth and development. 



This statement is intended not merely to deny and disprove the 

 statements on the subject which appear in text-books but also those 

 pernicious assumptions to the same effect which constantly appear 

 in the literature of the fertilizer trade. It is well to understand the 

 following clearly : 



(1) Certain chemical elements in the soil solution, including at 

 least nitrogen, phosphorus, sulphur, calcium, magnesium, iron and 

 potassium, are essential to normal plant growth. 



(2) These elements must be present in sufficient concentration 

 and the whole nutrient solution must be sufficiently concentrated. 



(3) Those elements must, regardless of the total concentration of 

 the solution, be in a proper balance among themselves. 



Beyond these conditions, we know little about the soil solution 

 which is above question. This is particularly pertinent regarding 

 the specific effects of the individual elements or the characteristics 

 of plants which the human senses can discern. 



WHAT ARE FERTILIZERS AND WHAT THEIR SOURCES? 



The problem of fertilizers and their application to soils, as it 

 stands today, is essentially a practical one. The truly scientific 

 phases of it which are being studied have not yet progressed far 

 enough to allow of much application of their results. Of necessity, 

 therefore, most rules and standards in fertilizer practice and in the 

 fertilizer industry must be more or less arbitrary. This includes, 

 of course, the determination of what constitutes a fertilizer material. 

 Nevertheless, it remains true beyond a peradventure that the final 

 decision in such matters must remain with the scientific investigator 

 of soil-and-plant problems. The reason for this is that he has delved 

 so deeply into the subject as to be cognizant of the numerous diffi- 

 culties and pitfalls which inhere in it, and thus knowing the limita- 

 tions of it can prescribe with much greater precision and justice 

 what should be adopted as a guide or guides. In accordance with 



