Sodium Hydroxide Direct Distillation: A Method for Estimating Total Nitrogen in Soil

Abstract

Soil total nitrogen (N) concentration is commonly measured by Kjeldahl and combustion methods. In this study, a method based on determination of ammonium (NH₄)‐N produced by steam distillation of the soil sample with sodium hydroxide solution (NaOH‐DD) is developed and evaluated for estimating soil total N concentration. The method was evaluated using two sample sets: (A) 44 samples collected from contrasting land uses in central Iran and (B) 344 samples collected from contrasting arable soils across Canada and Maine, USA. Based on this experiment, 10‐min distillation of 5.0 g soil with 20 mL 12.5 M NaOH were selected as the optimum conditions. The NH₄‐N released by the NaOH‐DD method was highly correlated with total N concentration in the sample sets A and B (r  =  0.79 and 0.94, respectively). The NaOH‐DD method provides a simple, rapid means of analysis with reduced measurement cost and better health and safety precautions than the traditional Kjeldahl method.

Current address for Mehdi Sharifi: Nova Scotia Agricultural College, Department of Plant and Animal Science, Truro, Canada.

Keywords:

• Combustion method
• Dumas method
• Kjeldahl method
• NaOH distillation
• soil total N

Notes

Current address for Mehdi Sharifi: Nova Scotia Agricultural College, Department of Plant and Animal Science, Truro, Canada.