Optical-Mechanical System for On-Combine Segregation of Wheat by Grain Protein Concentration

Published in Agron. J. 105:1529–1535 (2013) doi:10.2134/agronj2013.0206 Available freely online through the author-supported open access option. Copyright © 2013 by the American Society of Agronomy, 5585 Guilford Road, Madison, WI 53711. All rights reserved. No part of this periodical may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. G protein concentration is an important factor that determines the value of various cereal crops with premiums paid for high quality grain that meets the specific requirements of end users. In the United States, for example, brewers offer price premiums for malting barley (Hordeum vulgare L.) <120 g kg–1 (12%) GPC and millers may offer price premiums for soft white wheat <95 g kg–1 GPC. For the dark northern spring (DNS) subclass of hard red spring wheat, a premium is typically added to the price for each 2.5 g kg–1 change in GPC above a standard GPC of 140 g kg–1 whereas a discount is subtracted for each 2.5 g kg–1 in protein below this standard. For instance, premiums were U.S.$2.57 Mg–1 above 140 g kg–1 whereas discounts were U.S.$3.30 to U.S.$5.87 Mg–1 below 140 g kg–1 (14 June 2013 exporter bids for DNS wheat, Pacific Northwest Grain Market News, www.ams.usda.gov/mnreports/ lswpnwgrain.pdf). Analogous pricing structures exist in other grain-producing countries. Wheat protein varies significantly with position on a single head with greatest GPC at the base and least at the top (Bramble et al., 2002). Protein variability also occurs at larger scales within fields due to site-specific differences in soil fertility (Delin, 2004), topography (Fiez et al., 1994), plant available water (Stewart et al., 2002), and previous year’s cropping inputs (Long et al., 2008). However, growers tend to bin the grain together that is produced in a farm field based on an assumption that the wheat is homogenous. Conventional harvesting systems, which mix the grain together, lessen the ability of growers to capture premiums for high protein grain found in DNS wheat fields. By segregating grain by protein concentration, growers might be able to maximize revenues in markets that offer protein premiums. Thylén and Rosenqvist (2002) assumed that grain could be segregated either on the combine, hauling vehicles, or on-farm grain drier. They found that the size of protein premiums and magnitude of within-field GPC variability influenced the scale of production needed to cover equipment costs. Stewart et al. (2002) found that segregating durum wheat into two batches would have increased profits by AUS$34 ha–1 over conventional harvesting. Meyer-Aurich et al. (2008) investigated site-specific N fertilization and grain segregation for different price structures that varied as a function of GPC. Grain segregation, which isolated and sold valuable grain at higher prices, increased marginal returns by €50 ha–1 (U.S.$67 ha–1) over that of conventional harvesting. Martin (2012) found that revenue gains from segregating grain by GPC on the combine would vary with size of a price step in a price schedule with potential profits of more than U.S.$0.02 kg–1 for soft white winter wheat grown in Oregon. Whole grain analyzers based on the near infrared (NIR) spectroscopic techniques pioneered by Norris (1964) have been developed for combine harvesters and used for continuous in-line measurement of GPC across fields (Maertens et al., 2004; Long et al., 2008). These systems are reported to be accurate in ABSTRACT