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

2009; Wiley; Volume: 73; Issue: 4 Linguagem: Inglês

10.2136/sssaj2008.0165

1435-0661

Trenton L. Roberts, Robert J. Norman, Nathan A. Slaton, Charles E. Wilson, Jeremy Ross, Jacob T. Bushong,

Plant nutrient uptake and metabolism

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 15 N‐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 15 N 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‐ 15 N 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.