Determination of macro elements in alfalfa and white clover by near-infrared reflectance spectroscopy

Near-infrared reflectance spectroscopy was used to assess the mineral composition of both alfalfa (Medicago sativa L.) and white clover (Trifolium repens L.). Alfalfa (n = 230) and white clover (n = 97) plant samples from different locations in Uruguay representing a wide range of soil types were analysed. The samples were scanned for reflectance in a NIRSystems 6500 monochromator (NIRSysterns, Silver Spring, MD, USA). Predictive equations were developed using modified partial least squares (MPLS) with cross validation to avoid overfitting. The coefficients of determination in calibration (R-cal(2)) and the standard errors in cross validation (SECV) were 0.93 (SECV: 1.6), 0.95 (SECV: 1.3), 0.93 (SECV: 1.9), 0.88 (SECV: 2.7), 0.82 (SECV: 0.3) and 0.75 (SECV: 4.7) for alfalfa and 0.98 (SECV: 0.8),0.52 (SECV: 0.8),0.97(SECV:2.7),0.83(SECV:3.1),0.82(SECV: 1.9) and 0.45 (SECV: 2.6) for white clover, for N, Ca, K, P, Mg and S in g/kg on a dry weight respectively. Calcium, nitrogen and potassium were well predicted by NIRS in both alfalfa and white clover samples.