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NUTRIENT MANAGEMENT & SOIL & PLANT ANALYSIS

Direct Steam Distillation as an Alternative to the Illinois Soil Nitrogen Test

^a Crop, Soil, and Environmental Sciences Dep., 115 Plant Science, Univ. of Arkansas, Fayetteville, AR 72701
^b USDA-NRCS, 4900 Oklahoma Ave. Ste. 300, Woodward, OK 73801

^* Corresponding author (tlrobert{at}uark.edu).

Development of the Illinois Soil N Test (ISNT) has rejuvenated the search for a soil-based N test to measure potentially mineralizable soil N. Accurate quantification of amino sugar N has been achieved using the ISNT, but issues concerning sample variability and analysis time have led to the discovery of a 10 mol L^–1 NaOH direct steam distillation (DSD) procedure. Our primary objective was to determine if DSD could be used as a reliable alternative to the ISNT. Laboratory experiments were conducted to compare the two methods based on recovery of N from pure organic compounds, specificity tests to determine amine group hydrolysis, and recovery of ¹⁵N-labeled glucosamine N added to soils. Both methods recovered appreciable amounts of amino sugar N from pure compounds and the ISNT had a higher recovery of N from all amino sugar compounds. Recovery of N from glutamine and asparagine was higher using DSD. Direct ¹⁵N techniques for recovery of glucosamine N added to six soils showed no significant difference between the two methods within a soil, but resulted in significant differences among soils. Glucosamine-¹⁵N recovery significantly and positively correlated with soil total N. Although the ISNT and DSD measure different amounts of amino sugar N and transition amino acid N, they recover relatively the same amount of hydrolyzable N for a given soil, indicating that differences between the methods may not be that significant as both appear to quantify a pool of potentially mineralizable N. Direct steam distillation appears to be a viable alternative to the ISNT in correlation and calibration of crop response for N-fertilizer recommendations due to the short analysis time per sample (6 min) and the accurate estimation of potentially mineralizable N.

Abbreviations: DSD, direct steam distillation • DT, difference technique • ISNT, Illinois Soil Nitrogen Test

This article has been cited by other articles:

				T. L. Roberts, R. J. Norman, N. A. Slaton, and C. E. Wilson Jr. Changes in Alkaline Hydrolyzable Nitrogen Distribution with Soil Depth: Fertilizer Correlation and Calibration Implications Soil Sci. Soc. Am. J., October 21, 2009; 73(6): 2151 - 2158. [Abstract] [Full Text] [PDF]