Near infrared calibration of chemical constituents of Cajanus cajan (pigeon pea) used as forage

Near infrared reflectance spectroscopy (NIRS) was used to predict quality parameters in Cajanus cajan used as forage for animals. Crude protein (CP), neutral detergent fibre (NDF), acid detergent fibre (ADF), acid detergent lignin (ADL), crude lipid (CL) and organic matter (OM) were determined by chemical methods. The set of samples for analysis was selected using the software SELECT on the basis of the NIR spectra of samples from field plots and consisted of branches and leaves of Cajanus cajan, harvested in two contrasting locations in Zimbabwe. The samples were scanned and screened using an NIR Systems Model 5000 monochromator; 48 samples were used to calibrate and to cross-validate the equations derived. Equations for predicting chemical composition of the species under study were calculated using scores from partial least squares (PLS) as independent variables. Cross-validation procedures indicated good correlations between laboratory values and NIRS estimates. NIRS calibrations obtained from this study could be utilised in current and future programmes for evaluating the quality of Cajanus cajan forage for animal nutrition.