14 FERTILIZERS 



17. Soils vary in chemical composition according 

 to depth. The surface foot or two feet usually con- 

 tains the bulk of the nitrogen, due to the fact that 

 the nitrates are water soluble and the evaporation 

 of moisture at the surface leaves the nitrates and all 

 soluble plant foods there for the benefit of young 

 plants whose roots have not gone deep. Young 

 plants must grow first, and nitrogen produces 

 growth. As the plant matures, its roots penetrate 

 lower into the region where the nitrogen is scarce 

 and where the phosphates, silicon, lime and insoluble 

 elements are more evenly distributed. There, fruit 

 production and maturing of tissue take place. 



During the time growth is vigorous, fruit produc- 

 tion is limited or impossible even in the case of 

 mature trees when artificially forced to an abnor- 

 mally vigorous growth. 



18. While nitrogen is the chief element of growth, 

 other elements of the soil favor fruit production. 

 Phosphorus is definitely known to be one of these. 

 (70). If the fruit producing elements of the soil were 

 abundant on the surface, and nitrogen, relatively 

 deficient there, then fruit trees would be heavily 

 laden before they were taken from the nursery. 

 There is abundant evidence of order and design in the 

 methods of nature. "First the blade, then the ear, 

 then the full corn on the ear," and the soil is so 

 arranged as to effect the order. 



19. It is interesting to note briefly that the func- 

 tion of potassium is to mature the growth that 

 nitrogen produces. Where nitrogen is in excess of 

 potassium, as in bogs and peat lands, the growth is 

 soft and watery, whereas if potash is abundant and 



