Assessment of Soil Nitrogen Availability

Abstract

A limited number of field and laboratory studies have centered on developing definitive methods of assessing soil N availability, involving mineralizable as well as residual mineral N, and rigorous systems of predicting optimal N requirements of crops. Factors that need to be considered in assessing residual mineral N as a guide to N fertilization include scope and intensity of soil sampling, depth of sampling, and time of sampling. The presence of crop residues with high C/N ratios affects the net mineralization that occurs in short-term incubations. Efforts to develop suitable chemical indexes continue to be stimulated by the need for reliable and rapid methods of assessing soil N availability. The cumulative N taken up by a succession of crops in the greenhouse may be treated as a function of initial mineral N and relative soil organic N availability. The net supply of N made available to crops is a resultant of the complex biochemical process.