188 Fruit-growing in Arid Regions 



number are considered, ordinarily, in the fertilizing of soil, 

 namely, nitrogen, potassium, and phosphorus, because the 

 others are normally present in most soils or in the air 

 in sufficient amount. 



Nitrogen is essential to vigorous growth, and an over- 

 supply in the soil often promotes a rank growth of twigs 

 and foliage at the expense of fruit-production. 



Potassium or potash is especially important in fruit- 

 growing, since it aids in developing color and is the base 

 in combination with fruit acids. It also forms more than 

 50 per cent of the ash of fruits and constitutes a large pro- 

 portion of the ash of the wood of fruit trees. 



Phosphorus is probably not so important in fruit-grow- 

 ing as in grain production, as it enters largely into the com- 

 position of seeds. " But it is an essential constituent of tree 

 and fruit, and aids particularly in the proper ripening of the 

 latter. 



These three substances are supplied in various forms in 

 commercial fertilizers, and it would seem to be a simple 

 matter to provide any one or all of them as the individual 

 orchard seemed to demand. Such manures are used very 

 extensively by orchardists in the eastern states, but so 

 far as we know, commercial fertilizers have not been tried 

 in the orchards of the inter-mountain states, and we hope 

 that their use will not become necessary for many years to 

 come. In any event, freight rates are so high as to make 

 their use almost prohibitive. Then, the benefit to be 

 derived from their use under our conditions is problem- 

 atical, as the following experience would indicate. 



Potato-growers feel that they should grow two crops 

 in succession after turning under alfalfa sod. The second 



