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NUTRIENT MANAGEMENT & SOIL & PLANT ANALYSIS

Evaluation of Distillation and Diffusion Techniques for Estimating Hydrolyzable Amino Sugar-Nitrogen as a Means of Predicting Nitrogen Mineralization

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

^* Corresponding author (Jacob.Bushong{at}ok.usda.gov).

A rapid method to estimate soil N mineralization to improve N fertilizer recommendations has long been sought. Over the years, numerous methods to predict N mineralization have been proposed, but no one method has been widely accepted. Recently, researchers observed the concentration of hydrolyzable amino sugar-N in the soil correlated with crop N response. The objective of this study was to determine if developmental methods that quantify hydrolyzable amino sugar-N accurately predict N mineralization when compared to net-N mineralization by anaerobic incubation. Methods evaluated to predict hydrolyzable amino sugar-N were the Illinois soil nitrogen test (ISNT) by diffusion, and 2, 5, and 10 M NaOH direct steam distillation procedures. It was observed that the hydrolyzable amino sugar-N was a somewhat accurate predictor of N mineralization (R² = 0.38). However, when the hydrolyzable amino sugar-N concentrations were combined with the hydrolyzable NH₄–N concentrations, the ability to predict N mineralization improved (R² = 0.61). Suggesting more labile soil organic N forms along with amino sugar-N are potentially mineralizable. Rapid analytical procedures like the ISNT diffusion method and the 2, 5, and 10 M NaOH direct steam distillation techniques accurately predicted hydrolyzable amino sugar-N as well as hydrolyzable (NH₄ + amino sugar)-N. These methods also accurately predicted NH₄–N mineralized after anaerobic incubation. It could be assumed that this predictability may increase when soils are analyzed based on soil management, geographic area, and crop rotation. Glucosamine recovery was significant ( >85%, P = 0.05) for both methods showing their ability to quantify amino sugar-N in the soil as well as estimate the amount of potentially mineralizable-N. Lastly, in soil-testing facilities where the ISNT is already implemented as a procedure, the much quicker and equally reliable 10 M NaOH distillation technique may be used to achieve near identical test values.

Abbreviations: ISNT, Illinois soil nitrogen test