Laser-induced breakdown spectroscopy applied to cattle compost for phosphorus quantification

Authors

• Alberto Lencina * ¹
• Gustavo Romagnoli ²
• Andrea Alonso ³
• Noelia Ramos ²
• Cristian D’Angelo ^{4, 5}
• Lina Lett ³
• Silvia Mestelan ^{1, 3}

1. Laboratorio de Análisis de Suelos, Facultad de Agronomía, Universidad Nacional del Centro de la Provincia de Buenos Aires, Buenos Aires, Argentina
2. CRESCA, Facultad de Agronomía, Universidad Nacional del Centro de la Provincia de Buenos Aires, Buenos Aires, Argentina
3. CIISAS, Facultad de Agronomía, Universidad Nacional del Centro de la Provincia de Buenos Aires, Buenos Aires, Argentina
4. Instituto de Física Arroyo Seco, IFAS (UNCPBA) and CIFICEN (UNCPBA-CICPBA-CONICET), Buenos Aires, Argentina
5. Comisión de Investigaciones Científicas de la Provincia de Buenos Aires, Buenos Aires, Argentina

Abstract

Purpose Agronomic and environmental reasons force farmers to know the total P concentration of composted cattle manure. Laser-Induced Breakdown Spectroscopy seems proper to obtain such information. For logistic reasons (carriage, storage, field application, etc.), a dry matter characterization is also needed.
Method Thirty samples of feedlot compost at different stages of stability and maturity were studied. Samples were dried at 50°C for dry matter characterization. As a reference method to determine total P concentration, wet digestion and colorimetry were employed. The area of the P I line emission obtained by laser-induced ablation of the samples was measured to estimate the total P concentration. Randomized calibrations through a modified version of the Kennard-Stone algorithm based on the Mahalanobis distance were performed.
Results Dry matter varied from 40% to 90%, and no pattern was found related to compost origin, maturity, or stability. The total P concentration of the studied compost ranged from 1800 ppm up to 11200 ppm. Almost 80% of the calibration fittings have an R² ≥ 0.895. The mean validation error was less than 22% for about 80% of the calibrations, with a mean prediction error bound to 40%. Discarding outliers, the errors were reduced to 19% and 30%, respectively.
Conclusion Water content must be considered in addition to other characterizations due to logistic implications. Calibrations with a 30 percent of prediction error were achieved, which seems enough as a first approximation to predict the total P content in compost for utilization in farms to recycle nutrients.

Highlights

• Agronomic and environmental reasons force farmers to know the total P concentration of composted cattle manure.
• Laser-Induced Breakdown Spectroscopy seems proper to obtain such information.
• As a reference method to determine total P concentration, wet digestion and colorimetry were employed.
• Randomized calibrations through a modified version of the Kennard-Stone algorithm based on the Mahalanobis distance were performed.
• Discarding outliers, 80% of the calibration fittings have an R² ≥ 0.92 and the mean validation and prediction errors were reduced to 19% and 30%, respectively.

Keywords

• Feedlot compost
• Laser-Induced Breakdown Spectroscopy (LIBS)
• Nutrient recycling
• Total phosphorus concentration