158 TwENTT-FlEST BlBNNIAL EePOBX 



food elements in somewhat the same relative proportions 

 as found in the general composition of the earth's rock 

 crust. This embraces about all soils except sandy, muck, 

 and peat soils, which are found in this State in compara- 

 tively limited areas. 



Crops are composed chiefly of ten elements of plant 

 food, all of which are absolutely essential to plant 

 growth. Some other elements occur incidentally in 

 plants, but are not believed to be essential to growth, 

 and in any case the soil contains sufficient quantities of 

 them, so they may be left out of this discussion. 



The ten essential elements are carbon, hydrogen, 

 oxygen, nitrogen, calcium, magnesium, iron, sulphur, 

 phosphorus and potassium. Carbon, hydrogen and oxy- 

 gen constitute about 95 per cent, of the dry weight of 

 crops. The supply of carbon and oxygen is obtained 

 from the carbon dioxide of the air and is not under 

 human control. Hydrogen is obtained from water. 



Nitrogen is obtained entirely from the soil by all 

 non-leguminous crops (com, wheat, oats, grasses^ to- 

 bacco, etc.). Inoculated legume crops (clovers, peas, 

 beans, vetches, alfalfa, etc.) obtain their nitrogen from 

 the air whenever the soil supply is insufficient. 



All the other elements are obtained from the soil 

 by all plants. Of these, calcium, magnesium, iron and 

 sulphur are generally considered to be present in the soil 

 in sufficient quantities for maximum production. At 

 least, they may be assumed to be for the purpose of this 

 discussion, for the fertilizer trade is concerned only with 

 supplying phosphorus, potassium and nitrogen in fertil- 

 izers and prices are made on the basis of the content of 

 these elements. 



Manufacturers of complete fertilizers commonly as- 

 sume a deficiency in the soil of an available supply of 

 all three of these elements. As to the deficiency of phos- 

 phorus and nitrogen in most soils, we can readily agree, 

 for both chemical analyses of soUs and field tests support 

 this conclusion. As to the deficiency of potassium in 

 most soils, we cannot agree. Both chemical analyses 

 and field tests show normal soils to contain suffident 

 potassium for very large or maximum yields, provided 

 the content of organic matter is kept up to the necessary 



