Abstract
Livestock manure is widely applied onto agriculture soil to fertilize crops and increase soil fertility. However, it is difficult to provide real-time manure nutrient data based on traditional lab analyses during application. Manure sensing using near-infrared (NIR) spectroscopy is an innovative, rapid, and cost-effective technique for inline analysis of animal manure. This study investigated a NIR sensing system with reflectance and transflectance modes to predict N speciation in dairy cow manure using a spiking method. In this study, 20 dairy cow manure samples were collected and spiked to achieve four levels of ammoniacal nitrogen (NH4-N) and organic nitrogen (Org-N) concentrations that resulted in 100 samples in each spiking group. All samples were scanned and analyzed using a NIR system with reflectance and transflectance sensor configurations. NIR calibration models were developed using partial least square regression analysis for NH4-N, Org-N, total solid (TS), ash, and particle size (PS). Coefficient of determination (R2) and root mean square error (RMSE) were selected to evaluate the models. A transflectance probe with a 1 mm path length had the best performance for analyzing manure constituents among three path lengths. Reflectance mode improved the calibration accuracy for NH4-N and Org-N, whereas transflectance mode improved the model predictability for TS, ash, and PS. Reflectance provided good prediction for NH4-N (R2 = 0.83; RMSE = 0.65 mg mL−1) and approximate predictions for Org-N (R2 = 0.66; RMSE = 1.18 mg mL−1). Transflectance was excellent for TS predictions (R2 = 0.97), and provided good quantitative predictions for ash and approximate predictions for PS. The correlations between the accuracy of NH4-N and Org-N calibration models and other manure parameters were not observed indicating the predictions of N contents were not affected by TS, ash, and PS.
Highlights
Nutrients contained in animal manure are a valuable resource for crop growth when applied at agronomic rates
Two large broad peaks at approximately 1450 nm and 1950 nm resulting from the absorption by O-H bonds of water were observed in reflectance head sensor (HS) for both NH4 -N and organic nitrogen (Org-N) spiking samples
The reflectance sensor measures a fraction of the incident light that is backscattered at the sample surface and directed to the detection optics, while the transflectance probe is designed for measuring the transmitted part of the incident light through the sample and back to the detector thereafter, and the part of the signal comes from the backscattered light at the sample surface [31]
Summary
Nutrients contained in animal manure are a valuable resource for crop growth when applied at agronomic rates. Variability in manure nutrient concentrations [1] and traditional chemical analysis of manure composition [2] makes precise nutrient application difficult to achieve. It provides an alternative analytical technique to traditional analysis methods for determining the composition of animal manure based on the relationships between spectral and compositional properties of a set of samples. Traditional laboratory manure chemical analysis methods can be expensive ( for large sample numbers) and take significant time to obtain results. This time lag results in concentration data being available after
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