The determination of nitrogen by the Kjeldahl method gives an estimation of the total nitrogen in
. This test, often considered a chemical index, is essentially a test for total soil organic
matter, since the nitrogen concentration of soil organic matter is relatively constant. This measurement
does not estimate the rates of transformations of organic nitrogen into inorganic forms that are
available for plants; hence, many irregularities in predicting available nitrogen occur in its use.
However, considering that transformations depend on the type of organic matter, temperature, aeration,
water supply, acidity, and other factors, total nitrogen is likely as informative as determination
of other availability indexes.
Nevertheless, determinations of availability indexes have been
investigated extensively (96)