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

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 ۵۰°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 ۴۰% to ۹۰%, and no pattern was found related to compost origin, maturity, or stability. The total P concentration of the studied compost ranged from ۱۸۰۰ ppm up to ۱۱۲۰۰ ppm. Almost ۸۰% of the calibration fittings have an R۲ ≥ ۰.۸۹۵. The mean validation error was less than ۲۲% for about ۸۰% of the calibrations, with a mean prediction error bound to ۴۰%. Discarding outliers, the errors were reduced to ۱۹% and ۳۰%, respectively.Conclusion Water content must be considered in addition to other characterizations due to logistic implications. Calibrations with a ۳۰ 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. 

کلیدواژه ها:

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