Compositional analysis of cattle manure during composting using a field-portable near-infrared spectrometer

Composting of livestock manure is an effective method for managing the nutrients for agronomic purposes and reducing environmental and human health risks. Capability to analyze the biowastes on-site at the start of, periodically during, and at the end of composting could facilitate managing the composting process and increase the value of the end products. Near-infrared spectroscopy (NIRS) is well known for its capability to analyze organic substances rapidly and cost-effectively. This study was conducted to explore the capability of a field-portable NIR spectrometer to determine nutrient composition of beef feedlot manure when raw, stockpiled (not turned), and composted (windrowed and turned). Over a 2-yr period, beef feedlot manure mixed with bedding (wheat straw) was sampled annually at cleanout, after storage for some months in a large stockpile, and from windrows subjected to active thermophilic composting. Samples were dried and ground and scanned with the field-portable Corona 45 VIS NIR (visible/near-infrared) spectrometer (Carl Zeiss, Germany) from 360 to 1690 nm. NIRS was found useful in two ways. Classification analysis (Soft Independent Modeling of Class Analogy [SIMCA]) using the spectral data alone showed that stockpiling the manure did not change in composition significantly whereas compost was significantly, different from and less variable than raw or stockpiled manure. Second, by combining spectral and compositional data representing raw, stockpiled, and composted manure for both years, useful calibrations were developed for total C, organic C, total N, C:N, S, K, and pH. These calibrations can be used to rapidly predict these constituents in new samples. The calibration for P may be useful for screening, but those for nitrate + nitrite, available P, and Na were not successful. On the basis of analysis of dried samples, the field-portable NIR spectrometer was found successful for the rapid determination of C, N, and several other parameters in raw, stockpiled, and composted manure. For application of the technology on-site, these results need to be confirmed in further studies using moist, "as is" manure and compost samples.