It is capable of leaching or converting to nitrogen gas and lost. Colloid refers to both inorganic and organic matter. Colloids are usually considered to be very small particles of clay size. Atmospheric nitrogen is the N 2 gas in the air we breathe. This form of nitrogen is not available for direct use by plants.
Nitrification is the formation of nitrate from ammonium in soils by soil organisms.
Denitrification is the reduction of nitrate to atmospheric nitrogen gas. It is nitrogen gas freed by soil organisms in the absence of oxygen. The author wishes to acknowledge J.R. Brown, R.G. Hanson, H.N. Wheaton and J.L. Garrett, members of the Soil Testing Committee, for their contributions to this publication. Copyright 1999 University of Missouri. Published by University Extension , University of Missouri-Columbia.