Determinação colorimétrica de amônia volatilizada de solos fertilizados utilizando fotômetro UV-VIS portátil e de baixo custo.

Abstract

The constant increase in population is proportional to the search for improvements in food production chains. Brazilian agronomy faces several challenges to meet national and international demand, such as the lack of available land for planting, as the territory is limited. One way to increase production is through the use of nitrogen fertilizers, which provide the main nutrients necessary for plant development. One of the most commonly used nitrogen fertilizers is urea (CH₄N₂O), which provides a large amount of reactive nitrogen to the soil. However, urea is affected by the enzyme urease, which is responsible for transforming urea into ammonia and bicarbonate. The ammonia formed is lost to the atmosphere through volatilization, causing excessive use of fertilizers, which can contaminate the soil and the environment. The objective of this work is to develop a portable and low-cost analytical method to quantify the volatilized ammonia from fertilized soils using active sampling and in situ measurements. The method was based on the sampling of air containing NH3 by exposure to filter paper containing 100 µL of a 0.1 mol/L H2SO4 solution with a flow of 50 mL min-1. The colorimetric reaction used in the ammonia determination, with the "Toxic Ammonia for Freshwater" reagent kit, produces indophenol, a blue dye with maximum absorption at 630 nm. Absorption measurements were performed using a portable photometer built by 3D printing and using LEDs and a digital light sensor connected to an Arduino. The developed method provided a linear range in the interval of 64 to 258 ppbv of NH3 with 20 minutes of sampling. Finally, the method was applied to determine volatilized ammonia after 24 hours of fertilizer application.