Kinetics of ammonium volatilization in the form of ammonia in soils through a textural gradient

Abstract

Objective: To estimate the ammonia volatilization rate, using a texture gradient with increasing doses of ammonium in alkaline soils. Design/Methodology/Approach: The experiment took place in the Análisis Químico de Suelos lab of the Soil Department of the Universidad Autónoma Chapingo. The incubations consisted of 25 g of soil from the former Texcoco lake, with 12.5% clay. The soil was air-dried and sieved with a no. 10 mesh. The soil was mixed with three different concentrations (17.5%, 22.5%, and 32.5%) of bentonite, in order to increase clay content. The mixtures were placed in plastic containers with airtight seals. Twelve-point five mL of an ammonium sulfate solution (with 150, 300, 450, 600, and 750 mg of nitrogen kg soil-1) was added. The ammonia was recovered in a container with a boric acid solution. Volumetry was used to quantify ammonium. A completely randomized design with two factors (clay content and ammonium dose) was used. Data were analyzed with a regression analysis, analysis of variance, and Tukey Multiple Comparison Test, using the SAS OnDemand for Academics software. Results: The ammonia volatilization has a linear trend, with the concentration of the applied nitrogen. The volatilization rate ranged from 0.02 to 0.03 mg of ammonium per milligram of the nitrogen applied per kg soil-1. Significant statistical differences were recorded between the effect of the N dose and the clay content on the ammonia volatilization rate. Study Limitations/Implications: Clay content in the soil and ammonia volatilization rate can be used as an indicator to estimate ammonia losses and the ammonia adsorption capacity of the soil. Findings/Conclusions: Ammonia volatilization is independent from clay content and takes place immediately after its application. It has a linear trend regarding the ammonia dose applied. Ammonia volatilization rate decreases (asymptotic trend) as the clay content increases in the soil.