Near infrared reflectance spectroscopy for analysis of turf soil profiles

The evaluation of soil profiles is important in turf management. To characterize soil physical and chemical properties, samples can be sent to a laboratory for analysis. This process is time consuming and expensive, however. The use of near infrared reflectance spectroscopy to predict soil physical and chemical properties was investigated using turf soil profiles and compared with standard laboratory techniques. Turf soil profiles from Michigan State University (East Lansing) were scanned undisturbed and dried-ground with an NIRSystems 6500 monochromator (NIRSystems, Silver Springs, MD) by analyzing four depths each 1.25 cm thick. The reflectance measurements of monochromatic light were made from 400 to 2500 nm at 2-mn intervals. Computer-selected samples were analyzed in the laboratory for water content, organic matter, sand, silt, clay, and some chemical properties. The explained variance ranged from 0.16 for total N to 0.93 for sand. The organic matter, sand, silt, clay, P, Mg, and total N predictions were more accurate for the undisturbed samples than for the dried-ground samples. Expanding the Michigan State University database with turf soil profiles from Pennsylvania resulted in lower accuracies but broadened the application range of the calibration. More research is needed to improve the prediction accuracy of expanded databases before near infrared reflectance spectroscopy can be used to determine soil properties from golf greens or fairways of different locations.