Degree Type

Dissertation

Date of Award

1985

Degree Name

Doctor of Philosophy

Department

Agronomy

Abstract

The need for laboratory methods of obtaining an estimate of the amount of nitrogen (N) likely to be made available for crop growth by mineralization of soil organic matter during the growing season has long been evident, and numerous biological and chemical methods have been proposed. However, the methods showing the most promise are too complicated and time-consuming for use in soil testing laboratories, and there is an urgent need for a simple and rapid chemical method of assessing potentially available organic N in soil;Studies reported led to development of two rapid chemical methods of assessing potentially available organic soil N. One involves determination of the NH(,3)-N produced by steam-distilling the soil sample with pH 11.2 phosphate-borate buffer for 8 min. The other involves determination of the NH(,4)('+)-N produced by heating the soil sample with 2 M KCl at 100(DEGREES)C for 4 hours. Both methods are simple and precise, and their results are not significantly affected by air-drying or air-dry storage of the soil sample before analysis. They are well suited for use in soil testing laboratories because they do not require filtration or transfer steps. Studies using 33 Brazilian soils showed that the results obtained by these methods were highly correlated with those obtained by anaerobic and aerobic incubation methods of assessing potentially available organic N in soil;The two chemical methods developed were further evaluated by applying them to 30 Iowa soils and by comparing their results and those obtained by other chemical methods with the results of the aerobic and anaerobic incubation methods considered to be the best laboratory methods thus far proposed for assessment of potentially available organic N in soil. The chemical methods used included the acid KMnO(,4) method, the alkaline KMnO(,4) method, the CaCl(,2)-autoclave method, and the NaHCO(,3) UV method. The data obtained showed that the results of the two chemical methods developed were highly correlated with the results of the incubation techniques used for comparison and that the correlations observed with these two methods were higher than those observed with the previously proposed chemical methods. It is concluded that these two rapid and simple chemical methods are the best chemical methods thus far developed for assessment of potentially available organic N in soil and that they deserve consideration for use in soil testing laboratories.

DOI

https://doi.org/10.31274/rtd-180813-8686

Publisher

Digital Repository @ Iowa State University, http://lib.dr.iastate.edu/

Copyright Owner

Clesio Gianello

Language

en

Proquest ID

AAI8604465

File Format

application/pdf

File Size

96 pages

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