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

Abstract

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.

Mild and Moderate Extraction Methods to Assess Potentially Available Soil Organic Nitrogen

“…In Brazil, Otto et al (2013) considered ISNT a promising index for estimating potential responses to N fertilization in sugarcane cropping areas. An alternative method to ISNT is direct distillation (Bushong et al, 2008;Roberts et al, 2009), which exhibited similar extraction capacity and high correlation coefficients with ISNT (Bushong et al, 2008;Roberts et al, 2009;Otto et al, 2013); in addition, direct distillation does not require the use of Mason Jar, a container not readily available in the Brazilian market and which might limit adoption of the method.…”

Predicting Nitrogen Fertilizer Needs for Rice in Arkansas Using Alkaline Hydrolyzable-Nitrogen

“…Khan et al (2001) rekindled the search for a chemical method that could accurately predict crop response to N with the development of the ISNT. Th is simple diff usion method was able to quantify AH-N, primarily in the form of amino sugars (Kwon et al, 2009;Roberts et al, 2009a), and predict when corn (Zea mays L.) would respond to N fertilizer application. Although the ISNT had shown promise Th e immediate profi tability and long-term sustainability of domestic crop production have been threatened by increasing N fertilizer costs.…”

“…Further work by Bushong et al (2008) led to the development of a DSD technique as an alternative. Th e DSD technique has shown a strong correlation with the ISNT diff usion method while reducing analysis time and variability (Roberts et al, 2009a). …”

Field Validation of N-STaR for Rice Produced on Silt Loam Soils in Arkansas

“…Roberts et al (2011) was successful in developing a direct steam distillation method (Bushong et al, 2008;Roberts et al, 2009) that was highly correlated with rice total N uptake as well as RGY per-centage. The successful development of a calibration curve was achieved and resulted in a high coefficient of determination (r 2 = 0.89), but soils had to be sampled to a depth of 45 cm, which appears to be the effective rooting depth of rice grown on silt loam soils in Arkansas (Roberts et al, 2011).…”

“…Soil-water pH was measured with a glass electrode in a 1:2 soil/water (w/v) mixture. The direct steam distillation procedure as outlined by Bushong et al (2008) and Roberts et al (2009) was used to obtain the N-STaR soil test level, which involves a 7 min distillation using 10 mol L −1 NaOH. Nitrogen rate recommendations were determined using the N-STaR soil test value and N rate calibration equations that provided the N rates necessary to achieve 90, 95, and 100% RGY within a given location and correspond to N-STaR 90, 95, and 100% RGY, respectively, adapted from Roberts et al (2011) …”