Effect of grain density to near infrared spectra and design of a laboratory evaluation system for combine harvester

Abstract. Detection of grain quality on combine harvester in the field by near infrared (NIR) spectroscopy technology, which plays a significant role in grain moisture monitoring for feed quantity control of combine harvester, grain yield evaluation, and precision field management, has attracted more and more attention of farmers and researchers. However, it is difficult to measure the grain quality steadily due to a variety of complicated and changeful on-site factors, for example, grain density, which could not be constant during combine harvesting, may influence the spectral stability. In order to recognize the effect of grain density to the NIR spectra and control these interference factors, a laboratory study for different gradients of paddy samples‘ thickness with NIR reflectance spectroscopy was conducted. In this study, five different gradients, single layer sparse, single layer coverage, 10 mm thickness coverage, 15 mm thickness coverage and 20 mm thickness coverage, were set to illustrate the influence of grain density to NIR spectra. The result showed that 10 mm thickness coverage was the least thickness of grain national accumulation for an acceptable and effective NIR spectroscopy detection. With the enlightenment of the result, a design of a laboratory evaluation system mounted on the unloading device of combine harvester with grain flow thickness sensor was proposed.