Nitrogen Bacteria and Legumes / With special reference to red clover, cowpeas, soy beans, alfalfa, and sweet clover, on Illinois soils

UNIVERSITY OF ILLINOIS Agricultural Experiment Station.
BULLETIN NO. 94.
(With Special Reference to Red Clover, Cowpeas, Soy Beans, Alfalfa, and Sweet Clover, on Illinois Soils).
By CYRIL G. HOPKINS.
Work and Knowledge are a stronger team than Work and Work.
URBANA, ILLINOIS, FEBRUARY, 1904.


By CYRIL G. HOPKINS, Chief in Agronomy and Chemistry.
The nitrifying bacteria are those which have the power to form nitrates. In the following brief discussion of this subject we include at least three species of bacteria which by their combined or successive action have the power to transform organic nitrogen into nitrate nitrogen, which is a suitable form of nitrogen for plant food. For the exact information which we now have regarding the nitrifying bacteria we are indebted to the researches of Pasteur and Schlösing and Müntz of France, Winogradsky of Russia, Warington of England, and others.
This is the general process of nitrification in which the nitrifying bacteria transform or transfer the nitrogen from insoluble organic compounds into soluble compounds in which it may serve as available plant food. The nitrate which is thus formed may be calcium nitrate or magnesium nitrate or potassium nitrate or even sodium nitrate, depending upon which of these alkaline elements is present in the must suitable form. If no alkaline element is present in available form then no nitrates can be made in the soil. One of the reasons for applying ground limestone to soils which are deficient in lime is to furnish the element calcium in suitable form for the formation of nitrates in the process of nitrification. Ground limestone is calcium carbonate (CaCO₃), a compound containing one atom of calcium (Ca), one atom of carbon (C) and three atoms of oxygen (O₃). This is the same form of lime which is contained naturally in limestone soils—soils which are noted for their great productiveness—and it is generally the most economical form of lime to use for correcting soil acidity and promoting nitrification.