Kellogg and Orvedal n 



on these soils, but chemical nitrogen will not be enough. The organic 

 matter must also be maintained through the proper use of crop residues. 



Years ago, poor results from experiments with rock phosphate on 

 Chernozems led some to conclude that they would not respond to phos- 

 phate fertilization. Chernozem soils are too rich in calcium and too 

 high in pH for rock phosphate to become available. But later results 

 indicate that strong feeders, like sweet clover and alfalfa, may show 

 some responses even from rock phosphate. Greater increases, however, 

 are obtained from the more soluble phosphates, especially for small 

 grains and corn. This is partly because of depletion caused by long, 

 continuous cropping, but more because of better varieties and better 

 tillage practices that have made it possible for plants to use more phos- 

 phate efficiently. The use of phosphate is increasing and should increase 

 a great deal more. The need, however, is likely to vary a good deal 

 from one local type to another. 



Potassium generally is not needed on Chernozems, although there are 

 exceptions. It cannot be ruled out. Deficiencies of the minor nutrients 

 are uncommon but may be expected here and there, if other fertilizers 

 are used abundantly and especially with supplemental irrigation. 



Desert soils 



The soils of the desert are well supplied with mineral plant nu- 

 trients, except for the very sandy ones, but are low in organic matter 

 and nitrogen. Often the mineral nutrients are poorly balanced, with 

 excesses of some. Without irrigation, these soils are used only for ex- 

 tensive grazing, and moisture is the limiting factor for plant growth 

 rather than fertility. Where irrigated, however, fertility problems be- 

 come highly important. With technically sound irrigation and opti- 

 mum moisture conditions, the ceiling set on nonirrigated soils by the 

 moisture supply is lifted and other factors become limiting. 



Of first importance is nitrogen. With legumes in the rotation, some 

 nitrogen may be supplied by them, but ordinarily commercial fertilizer 

 is also needed. Potassium is usually abundant in desert soils, but phos- 

 phorus is commonly low. Then too, deficiencies of the minor nutrients, 

 like iron and zinc, are common. These conditions are partly stimulated 

 by the high amounts of lime generally present. The fertility problems 



