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ENVIRONMENT, WELL-BEING, AND BEHAVIOR |


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* College of Engineering, China Agricultural University, Beijing 100083, China;
Industrial Technology Service Center, Chinese Academy of Agricultural Mechanization Sciences, Beijing 100083, China; and
Key Laboratory of Modern Precision Agriculture System Integration, Ministry of Education, Beijing 100083, China
2 Corresponding author: hanlj{at}cau.edu.cn
| ABSTRACT |
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Key Words: near-infrared reflectance spectroscopy modified partial least squares layer manure prediction
| INTRODUCTION |
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Traditional analyses in the laboratory have provided great precision, but these have come at the expense of time and resources and have not been attractive to many farmers, or even practical for farming application of animal manure (Lugo-Ospina et al., 2005). Therefore, there has been a continuing interest in rapidly estimating nutrient concentration of livestock manure. These rapid estimation methods can be subdivided into 2 types: physicochemical models and near-infrared reflectance spectroscopy (NIRS) models. The former relate nutrient concentrations to the physicochemical properties (e.g., specific gravity, electrical conductivity, pH). The latter apply NIRS information to describe nutrient concentrations. Compared with physicochemical models, NIRS models offer the possibility of rapid analysis of samples without generating chemical waste. In addition, the NIRS method often requires little or no sample preparation and can determine several constituent concentrations simultaneously. Once NIR calibration models are obtained from the laboratory, they can be applied to field-portable or mobile NIR instrumentation, which has the potential for real-time analysis during the spreading of manure.
The NIRS technique has been applied extensively for the analysis of constituents in livestock manure. Previous work has demonstrated the potential of NIRS for the rapid evaluation of moisture or DM content, organic matter (OM), total N (TN), ammonium N (AN), total P (TP), and total K (TK) in dairy, poultry, swine, and cattle manures (Nakatani and Harada, 1995; Nakatani et al., 1996; Kinoshita et al., 1997; Smith et al., 1999; Millmier et al., 2000; Reeves and Van Kessel, 2000a,b; Reeves, 2001a,b; Malley et al., 2002; Saeys et al., 2004). Recently, our laboratory also presented an NIRS model to predict nutrient contents in fattening pig manure obtained from floor scrapings (Yang et al., 2006). Because of the differences in the diets and physiology of livestock species, the manure produced by each has different chemical and physical properties. For example, dairy manure is a slurry with a high moisture concentration (80 to 95%), but may also contain large amounts of straw or other bedding materials (Reeves, 2001a). Layer manure, on the other hand, is generally much drier but contains minerals such as Mg and Cu. A study by Reeves and Van Kessel (2000a) indicated that the variation in sample composition had a drastic effect on the spectra. Therefore, further work is needed to determine the feasibility and limitations of using the NIRS method to analyze layer manure. The object of this study was to determine the possibility of NIRS to predict the composition different of layer manure samples quickly and accurately, and then to establish NIRS calibrations on layer manure samples.
| MATERIALS AND METHODS |
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Wet Chemical Analysis
Chemical analysis of the contents included moisture, OM, TN, AN, TP, TK, Mg, Cu, Fe, and Na. Analysis was done by conventional chemical procedures as detailed in Table 1
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Statistical Analysis
Mathematical treatment of the spectral data was performed by using Spectrum Quant+ software (PerkinElmer). Near-infrared reflectance spectroscopy calibration was developed by means of modified partial least squares regression. The following mathematical treatments were applied separately and simultaneously, and then compared to choose the best treatment combination: smoothing, derivative, standard normal variate, and normal multiplicative scatter correction. Cross-validation was carried out to select the optimal number of terms in the equation and so to avoid overfitting. The data set was sorted by composition, and 1 of the 4 samples was removed for the validation sample. The mathematical treatment giving the lowest root mean square error of cross-validation on the whole data set for each parameter was applied to the calibration set, and the resultant equation was used to predict the validation set. The following statistical parameters were considered: the correlation coefficient of calibration (r2), the correlation coefficient of cross-validation (rcv2), the correlation coefficient of validation (rv2), the root mean square error of calibration, and the root mean square error of cross-validation. The ratio of SD over root mean square error of prediction, called the ratio of prediction to deviation (RPD), is the factor by which the prediction accuracy has been increased compared with using the mean composition for all samples. Based on the RPD value, 5 levels of prediction accuracy were considered in this study for a very heterogeneous material such as manure. A value for the RPD below 1.5 indicates that the calibration is not usable. A value for the RPD between 1.5 and 2.0 reveals the possibility of distinguishing between high and low values, whereas a value between 2.0 and 2.5 makes approximate quantitative predictions possible. For values between 2.5 and 3.0, and above 3.0, the prediction is classified as good or excellent, respectively (Saeys et al., 2005).
| RESULTS AND DISCUSSION |
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Constituent Partial Least Squares Type 1 Calibration (Three-Fourths of the Samples)
The partial least squares results based on three-fourths of the samples are presented in Table 4
. Comparison of the rcv2 on the whole data set with the r2 on the calibration set showed that all calibrations were robust. Both the one-out cross-validation results and the final calibration were quite good for moisture, TN, AN, and OM; moderate for TP; and poor for TK, Cu, Fe, Mg, and Na.
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For TP, the rv2 value (0.80) and the RPD value (2.01) indicated the possibility of making approximate predictions. Phosphorus in the manure arose from 2 major sources: undigested phytate and excess dietary phosphate (Malley et al., 2002). At present, there are different opinions on the predictability of TP by the NIRS method. The reports of some researchers have indicated that P in poultry (Reeves, 2001a), dairy (Millmier et al., 2000; Reeves and Van Kessel, 2000b), and hog (Millmier et al., 2000) manure cannot be predicted successfully by the NIRS method. However, other researchers have demonstrated that the NIRS method can be applied to predict P concentration in hog (Malley et al., 2002) and broiler (Smith et al., 2001) manure. The reason may be attributed to the presence of spectrally active P bonds. Some studies have suggested that P may exist in forms detectable by NIRS, at least in some grasses and legumes (Clark et al., 1987; Saiga et al., 1989). DeBoever et al. (1994) reported that the P in feed-stuffs could be predicted by NIRS, with an rv2 of 0.94 to 0.96 and a standard error of prediction (SEP) of 0.08.
For TK, Mg, and Na, rv2 values between 0.58 and 0.62 and RPD values between 1.5 and 2.0 indicated that only a distinction between low and high concentrations could be made. For Cu and Fe, rv2 values between 0.48 and 0.55 and RPD values below 1.5 indicated that the calibrations were not usable. These results were consistent with previous studies (Reeves, 2001a; Yang et al., 2006). The poor prediction results for TK, Cu, Fe, Mg, and Na could be explained by the fact that there was a lack of spectral absorption for minerals in the NIR region and that calibrations were generally not good because they depended on the relationships between organic components and the minerals, which are indirect or surrogate calibrations (Shenk et al., 1992). The problem with such surrogate calibrations is that they are only as accurate as the correlation between the organic component and the mineral of interest and can easily produce erroneous results (Yang et al., 2006).
In conclusion, this is one of the first studies to use NIRS to predict the constituents in layer manure. Results demonstrated that NIRS analysis of layer manure samples can provide accurate prediction of a wide range of chemical components, including moisture, OM, TN, and AN. This study presented the opportunity to use the NIRS technique to determine the content of layer manure samples. Further efforts with larger data sets are needed to better determine the feasibility of, limitations of, and requirements for developing accurate and robust calibrations of manure constituents by using the NIRS technique.
| ACKNOWLEDGMENTS |
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| FOOTNOTES |
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Received for publication November 18, 2007. Accepted for publication March 26, 2008.
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