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<p>Non-destructive, reagent-free, and cost-effective detection of soil macronutrients like nitrogen (N), phosphorus (P), and potassium (K) is vital for precision crop management. Visible (Vis) spectroscopic techniques not only fulfills these but also offer advantages over other spectroscopic methods in terms of cost, simplicity and lesser sensitivity towards water. While conventional Vis spectroscopy-based methods generally rely on colorimetric detection, they often suffer from sample contamination due to the use of chemical reagents and exhibit slower response times. To overcome these limitations, we developed a custom-built Vis spectroscopic system designed for reagent-free detection. The system enhances sensitivity by integrating a high-intensity broadband light (1000&#xa0;W) source, a precision monochromator, a silicon (Si) photodetector, and a lock-in amplifier–based detection scheme. This setup enables precise measurement of absorbance across specific wavelengths, improving signal-to-noise ratio and allowing accurate quantification of N, P and K concentrations in processed soil samples without the need for additional chemical processing. Nonlinear fitting models for N, P and K were developed by correlating the total absorbance (per cm path length) of fertilizer-derived standards with their respective concentrations. These models were subsequently applied to predict NPK quantities in processed soil samples. The models achieved coefficient of determination (R<sup>2</sup>) values greater than 0.9, indicating strong predictive performance and a robust fit between absorbance and nutrient concentration The corresponding sensitivities obtained were 0.00637&#xa0;g/cc, 0.0006&#xa0;g/cc and 0.06703&#xa0;g/cc per unit absorbance for N, P and K respectively. The RMSE achieved were 6.26 × 10<sup>− 7</sup> gm/cc, 2.6 × 10<sup>− 8</sup> gm/cc and 1.46 × 10<sup>− 6</sup> gm/cc for N, P and K respectively demonstrating a high accuracy in nutrient concentration estimation. In near-future, the work may be used for in-situ measurement of soil nutrients concentrations.</p>

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Estimation of soil macro-nutrients using visible optical transmission spectroscopy

  • 期刊论文

  • 发表日期：

    2025年7月17日

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  • Suman Kumar Pal,
  • Syamsundar De,
  • Shyamal Kumar Das Mandal,
  • Pranabendu Ganguly

摘要

Non-destructive, reagent-free, and cost-effective detection of soil macronutrients like nitrogen (N), phosphorus (P), and potassium (K) is vital for precision crop management. Visible (Vis) spectroscopic techniques not only fulfills these but also offer advantages over other spectroscopic methods in terms of cost, simplicity and lesser sensitivity towards water. While conventional Vis spectroscopy-based methods generally rely on colorimetric detection, they often suffer from sample contamination due to the use of chemical reagents and exhibit slower response times. To overcome these limitations, we developed a custom-built Vis spectroscopic system designed for reagent-free detection. The system enhances sensitivity by integrating a high-intensity broadband light (1000 W) source, a precision monochromator, a silicon (Si) photodetector, and a lock-in amplifier–based detection scheme. This setup enables precise measurement of absorbance across specific wavelengths, improving signal-to-noise ratio and allowing accurate quantification of N, P and K concentrations in processed soil samples without the need for additional chemical processing. Nonlinear fitting models for N, P and K were developed by correlating the total absorbance (per cm path length) of fertilizer-derived standards with their respective concentrations. These models were subsequently applied to predict NPK quantities in processed soil samples. The models achieved coefficient of determination (R2) values greater than 0.9, indicating strong predictive performance and a robust fit between absorbance and nutrient concentration The corresponding sensitivities obtained were 0.00637 g/cc, 0.0006 g/cc and 0.06703 g/cc per unit absorbance for N, P and K respectively. The RMSE achieved were 6.26 × 10− 7 gm/cc, 2.6 × 10− 8 gm/cc and 1.46 × 10− 6 gm/cc for N, P and K respectively demonstrating a high accuracy in nutrient concentration estimation. In near-future, the work may be used for in-situ measurement of soil nutrients concentrations.