Adapting a relatively low-cost reflectance spectrometer for on-combine sensing of grain protein concentration

摘要

An on-combine, near infrared (NIR) spectrometer is now commercially available for mapping grain protein concentration (GPC) within farm fields. Costing > US$20,000, this specialized instrument may not be affordable for all producers. The objective of this study was to adapt and evaluate a moderately priced reflectance spectrometer ( < US$5500, Avantes AvaSpec ULS2048 x 16-USB2) for on-combine sensing of GPC. A "leave-one-out" cross-validation partial least square (PLS) regression model for GPC was developed for flowing grain with the spectrometer's probe-head attached to the lower end of an inclined trough. Good correlation (r(2) = 0.92) was observed between estimated and reference GPC in grain samples when NIR spectra (850-1040 nm) and GPC reference values were used for developing the PLS model. The NIR estimation achieved a standard error of < 5 g of protein kg(-1) of grain. An inexpensive external temperature control system was built that stabilized the temperature of the instrument's input/output converter board within 60 m of activation. Placed on a test stand machine with standard 12.5 cm diameter auger, the instrument predicted GPC to < 5 and < 10 g kg(-1) in two and three of four wheat cultivars thus indicating that the model produced on the trough may be applied into predicting GPC on a combine. When placed on a combine, the calibrated instrument produced a protein map that correlated well (r = 0.88) with a map derived from an expensive reflectance spectrometer (US$32,000, Polytec 1721). Thus, a relatively inexpensive NIR reflectance spectrometer may be adapted for mapping GPC across fields.