Determinação de amônia volatilizada de solos fertilizados com fotômetro uv-vis portátil e de baixo custo

Abstract

The continuous growth of the world population has increased the demand for more efficient food production systems. In Brazil, the agricultural sector faces significant challenges in meeting both domestic and international markets, especially due to the limitation of available land for cultivation. In this context, the use of nitrogen fertilizers stands out as a widely adopted strategy to increase productivity, as it provides essential nutrients for plant development. Among these inputs, urea (CH₄N₂O) is one of the main sources of nitrogen used in agriculture. After its application to the soil, urea is rapidly hydrolyzed by the action of the enzyme urease, resulting in the formation of gaseous ammonia and bicarbonate. This process reduces fertilizer efficiency, increases production costs, and may cause negative environmental impacts, mainly due to ammonia volatilization. Given this scenario, the present work proposes the development of a portable analytical method capable of quantifying volatilized ammonia in fertilized soils through active sampling and measurements carried out directly in the field. The experimental procedure consisted of collecting air containing NH₃ by bubbling it through a sulfuric acid solution with methyl orange, using a flow rate of 50 mL·min⁻¹. Absorbance readings were performed using a portable photometer produced by 3D printing, equipped with a 490 nm wavelength LED, a digital optical sensor, and an air pump, all integrated into an Arduino microcontroller. The method showed linear behavior in the range of 0 to 3.0 × 10⁻⁶ mol of NH₃, considering a collection time of 20 minutes. In addition, its application allowed the quantification of volatilized ammonia over four days, with collections carried out every 24 hours after fertilizer incorporation into the soil. As a form of validation of the sampling procedure, a parallel test was conducted in the Technical Assistance laboratory of Adfert. In this test, the quantification of ammonia resulting from urea volatilization in the soil was performed by titration of the solution obtained from filter papers used to capture the analyte.