Use of Near Infrared Reflectance Spectroscoppy to Screen Soybean Lines for Plant Nitrogen
Selecting breeding lines of soybean [Gfycine Max (L.) Merr.] for an enhanced ability to support N fixation by Bradyrhizobium japonicum Jordan requires a fast screening method for determining N content in the plants. The objective of this study was to determine if near infrared spectroscopy (NIRS) could be used as such a method. Two cultivars grown at two locations with 10 inoculation treatments were used for field samples. One cultivar grown at two temperature regimes with 40 N fertilizer treatments was used for the phytotron samples. Samples were ground and regressions were run of log (I/relectance) of up to 19 filters (wavelengths) on a Technicon InfraAlyzer 400 (Technicon Instruments Corp., Tarrytown, NY) to laboratory Kjeldahl N determinations. Filters were selected to optimize regressions; overall stage and/or part regressions as well as individual stage and/or part (R2, R8—overall top growth, R8—seeds, and R8—top growth excluding seeds) regressions were carried out. Tests of homogeneity of regressions showed that stages and/or parts could not be combined, but that field and phytotron-grown soybean could be combined. Predictions run on random samples were most accurate for N content in seeds and at R2 and least accurate for R8—top growth excluding seeds. Calibrations based on field and phytotron samples from 1 yr were acceptable for predicting N content in a subsequent year. The NIRS calibrations were on the average more highly repeatable for predicting N content than either one of two Kjeldahl determinations.
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