An Evaluation of Nitrogen Mineralization Indices for Organic Residues
- B.F. Douglas and
- F.R. Magdoff *
Organic residues without high levels of toxic metal or organic constituents are usually applied to agricultural soils at rates based on assumed contributions of available N to the growing crop. However, there is no accepted test for assessing potential available N supply from residues. Although the actual contribution will depend on soil characteristics and climate as well as residue characteristics, a chemical index might be useful in ranking residues according to potential available N contributions. An experiment was conducted to evaluate a number of chemical indices for N availability. The 19 residues used in the study consisted of seven types of manures, six sewage sludges, and six composted or mixed soil amendments. Organic residues were mixed with sandy top-soil and perlite and incubated in glass tubes in the laboratory for 67 d. Total N, total Kjeldahl N, organic N, and N released into the Walkely-Black acid-dichromate digest (WBN) were significantly correlated with the amount of N mineralized as well as the fraction of organic N mineralized during the incubation. The best relationship for the amount of N mineralized was with WBN (r2 = 0.89 for a quadratic relationship). The strongest of the correlations for fraction of organic N mineralized was also with WBN (r2 = 0.82).Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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