Métodos Kjeldahl, Elementar e o Potencial da Espectroscopia do Infravermelho Próximo para Determinação de Nitrogênio em Solos da Bacia do Acre

Abstract

The Acre basin comprises a distinct geological environment with different environments in relation to Amazon biome, which results in soils with mineralogical and chemical properties different of other soils of this biome. For these environment there are no evaluations regarding the accuracy and precision of analysis methods for nitrogen: Kjeldahl, dry combustion and NIR spectroscopy. The objective of the research was to assess and compare two conventional methods and near infrared spectroscopy to determine the nitrogen content in the Acre basin soil. To evaluate these three methods, were used 176 representative soil samples of Acre basin. To evaluate the applicability of NIR was adopted as reference the levels determined by the elementary method, the NIR spectra are used in the range 1100-2500 nm and 2.0 nm resolution by diffuse reflectance. The Kjeldahl and dry combustion methods showed no differences in determining the nitrogen content in the soil, and both methods showed coefficient of variation of less than 5%, indicating the same accuracy of the two methods for determining the nitrogen contents in the Acre Basin soil. Adopting the elemental analysis to calibrate and validate the estimates of nitrogen in the soil by near infrared spectroscopy, there was obtained the standard error of calibration 0.28 g kg -1 and coefficient of determination of 84%; and the standard validation error model was 0.35 g kg -1 with the coefficient of determination of 77%. This has been interpreted as NIR spectroscopy has potential to be used in the quantification of the nitrogen content in the soil in research that require high-volume data processing. Keywords : soil testing; elemental analysis; Amazon; green chemistry.