144 



CALIFORNIA FRUITS: HOW TO GROW THEM 



Only a very small proportion of the weight of plant substance, there- 

 fore, consists of the other seven essential elements. The amounts 

 of these substances contained in some of our fruits is shown approxi- 

 mately in the following table, taken from analyses made by Pro- 

 fessor G. E. Colby, formerly of the California Agricultural Ex- 

 periment Station : y 



Quantities of Soil Ingredients Withdrawn by Various Fruits 



tincluding hulls. *Estimated. 



Why Such Analyses May Not Be a True Guide in Fertilization. 

 A little calculation on the basis of the data in the foregoing table 

 will make it quite clear that a ten-ton crop of fresh grapes would 

 only remove from the soil about 51 pounds of potash, 5 pounds of 

 lime, 2.2 pounds of phosphoric acid and 25.2 pounds of nitrogen. 

 A very large crop of fresh apricots (about ten tons) would remove 

 from the soil about 60 pounds of potash, 3.20 pounds of lime, 13.20 

 pounds of phosphoric acid and 38.80 pounds of nitrogen. Now even 

 a very poor soil contains in the upper three feet per acre, which are 

 only a portion of the plant roots' foraging area, about 12,000 pounds 

 each of potash and lime, about 6,000 pounds of phosphoric acid and 

 about 3,000 pounds of nitrogen. Moreover, some of the portions of 

 the fruit are frequently returned to the soil, and irrigation waters, 

 where such are used, most commonly carry in solution large enough 

 quantities of the essential elements to more than make up for the 

 losses sustained through the removal of the fruit crop. This kind 

 of reasoning, coupled with the fact that even moderately good soils 

 may contain ten times as much potash and lime, twice as much 

 phosphoric acid, and three times as much nitrogen as the poor soil 

 cited, and also the fact that much more than three feet of soil in 

 depth are frequently available for root development, make it very 

 clear that the essential elements are found in nearly all soils in 

 quantities sufficient to last for centuries. Of course, these are 

 definite quantities and if we consider our obligations to posterity 

 we should contemplate ways and means for preventing unusual and 



