Near-infrared reflectance spectroscopy prediction of leaf and mineral concentrations in alfalfa

Rapid and accurate prediction of leaf and mineral concentration of alfalfa (Medicago sativa L.) forage would be valuable for dried research and farm hay samples because current approaches are time-consuming and expensive. Our objective was to study the effectiveness of near-infrared reflectance spectroscopy (NIRS) in determining the leaf concentration in dried alfalfa forage and the concentration of total ash and minerals in leaves and stems. Leaf concentration in sun-cured hay samples from several years was accurately predicted using NIRS with standard errors of cross validation (SECVs) of 34 to 49 g kg(-1), but equations had to be redeveloped with samples representing each year. Equations derived from dried research samples had SECVs of 37 to 39 g kg(-1) but still required equation redevelopment each year. Near-infrared reflectance spectroscopy accurately predicted total ash and Ca, K, and P of leaves and stems of alfalfa hay and research samples but was less consistent in prediction of Mg and S and microminerals Al, B, Fe, Mn, and Si in leaves and stems. We failed to develop any useful equations for Na. Leaves had higher concentrations of total ash and most minerals than stems, except for K, Cd, Cu, Ni, and Cr. Near-infrared reflectance spectroscopy is a rapid and accurate method for determining leaf, total ash, and Ca, K, and P concentration in sun-cured hay and oven-dried research samples. Near-infrared reflectance spectroscopy would be especially useful in an electrical generating facility using large quantities of alfalfa as a biofuel.