Quantitative Analysis of Added Ammonium and Nitrate in Silica Sand and Soil Using Diffuse Reflectance Infrared Spectroscopy

Abstract

Diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) in both near infrared (NIR) and mid infrared (MIR) has been previously shown to be effective in quantifying soil nitrogen concentrations when calibrated using numerous field soil samples. However, such an approach incorporates samples that may contain substantial correlations between physical and chemical properties. To address these concerns, the performance of DRIFTS coupled with PLS regression in NIR regions, 5000–4000 cm^− 1 (2000–2500 nm) and 6500–5500 cm^− 1 (1540–1820 nm), and the MIR region, 3400–2400 cm^− 1 (2940–4170 nm), was assessed through analysis of the concentration of ammonium (NH₄ ⁺) (0–50 ppm) and nitrate (NO₃ ⁻) (0–200 ppm) artificially incorporated into a series of silica sand samples with a consistent particle size. The influence of different particle sizes of sand was also analyzed quantitatively. The Pima clay loam soil was then evaluated with concentration ranges of 0–200 ppm NH₄ ⁺ and 180–1000 ppm NO₃ ⁻ added to the soil samples. With sand samples, accurate NH₄ ⁺ measurements could be performed using all three ranges. The MIR region was significantly more useful for NO₃ ⁻ measurement than those of NIR regions. The MIR region also performed reasonably well with soil samples but both NIR regions provided poor results. The detection limits for NH₄ ⁺ and NO₃ ⁻ measurements in sand were 9 ppm NH₄ ⁺ and 39 ppm NO₃ ⁻ with the correlation coefficients (R²) of roughly 97% and 96%, respectively, and in soil were 100 ppm NH₄ ⁺ and 330 ppm NO₃ ⁻ with the correlation coefficients (R²) of roughly 80% and 90%, respectively.

Keywords:

• DRIFTS
• Mid infrared
• Near infrared
• Ammonium
• Nitrate
• Sand
• Soil