MADISON, WI, May 4, 2009--Contrary to the prevailing view, cereal crops derive the majority of their nitrogen from the soil, not fertilizer. Soils differ considerably in microbial activities that determine nitrogen-supplying power, and these differences must be taken into account if nitrogen fertilizers are to be used efficiently. The Illinois Soil Nitrogen Test (ISNT) was developed for this purpose, and involves estimation of gaseous ammonia liberated by heating the soil with strong alkali in a Mason jar. Several studies have provided evidence that the ISNT is predictive of yield response by corn to nitrogen fertilization, but there have also been negative evaluations in which concern has been raised that test values represent a constant proportion of total soil nitrogen rather than a microbial fraction that would be potentially available.
A study was conducted from 2004 to 2006 at the University of Illinois to clarify the chemical nature of what the ISNT measures and its relationship to microbial growth in agricultural soils. A multifaceted approach was taken, involving recovery tests with pure organic nitrogen compounds, statistical analyses of different nitrogen fractions measured for 26 Illinois agricultural soils, and incubation studies to determine incorporation of labeled nitrogen into soil nitrogen fractions. Results from the study were published in the May-June issue of the Soil Science Society of America Journal. The research was funded by the USDA and the Illinois Council on Food and Agricultural Research (C-FAR).
Recovery tests did not support the concept that the ISNT estimates total soil nitrogen. Rather, the results confirmed that the ISNT is selective for certain forms of microbial nitrogen, and differs from conventional acid-hydrolyzable fractions in the proportions of these compounds that are detected. Specifically, amides and the amino sugars in bacterial cell walls were detected, but not alpha-amino acids or fungal
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| Contact: Sara Uttech suttech@soils.org 608-268-4948 Soil Science Society of America Source:Eurekalert |