Soil testing is an important task for precision farming and soil quality assessment. However, the standard procedures for soil testing are usually very complex, expensive, and time-consuming. Near-infrared reflectance spectroscopy (NIRS) is a rapid and convenient analytical technique. The main objective of this project was to study the potential of NIRS for analyses of soil analyses. In the study of soil mixtures containing diverse sources of C and N, the results indicated that NIRS can be used to quantify soil C (organic C and inorganic C) and total N, C:N ratios simultaneously. In the study of moist and air-dried soil samples from agricultural fields in Iowa and Minnesota, the results indicated that NIRS predictions of tested soil properties were more accurate for air-dried soils than moist soils; however, the differences were minimal. The overall ability of NIRS to predict soil properties was based on the analyses of 33 properties for over 800 soil samples collected from four Major Land Resources Areas (9, 67, 77, and 105). The results indicated that NIRS can be used to simultaneously estimate soil C and N, moisture, CEC, basal respiration rate, potentially mineralizable N, particle size distribution, and some extractable and exchangeable cations with acceptable accuracy. Based on these studies NIRS has the potential to be used as a fast and nondestructive soil testing technique for both moist and air-dried soils.
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