Effects of machine-crop parameters on mechanical grain damage in rice threshing

Abstract

Improper mechanical threshing can lead to fissuring and breakage of rice grains, resulting in lower milling quality and increased quantity losses, especially in locally produced rice in Africa due to poor post-harvest practices. This study examined the effects of moisture content (MC), drum peripheral speed (DS) and spike spacing (SS) on grain damage during threshing of three locally grown rice varieties: Shaga, Ediget and Nerica-4. Hand threshing served as the control group. Fissured and broken grain varied significantly by variety, MC, DS, SS and interaction effects. Ediget variety had the highest percentage of fissured grain, while Nerica-4 had the highest percentage of broken grain. As MC increased from 11.44% to 24.01%, fissured and broken grains decreased significantly for all varieties. As DS increased from 17.3 to 24.6 m/s, fissured and broken grain also increased. As SS decreased from 80 to 60 mm, fissured and broken grain increased. Furthermore, the interaction effects also affect grain fissuring and breakage significantly. In general, lower grain fissuring and breakage was observed at highest MC (23.43–24%), lower tip DS (17.3 m/s) and wider SS (80 mm) for all studied varieties. Pre-threshing grain fissuring and breakage had a greater contribution to overall grain damage at lower MC levels. Harvest MC was found to be the most influential factor affecting fissured and broken grain, followed by DS and SS. Overall, these results highlight the importance of proper threshing techniques and highlight areas where improvements can be made to reduce post-harvest losses and improve rice quality.

Keywords

• Rice threshing
• moisture content
• drum peripheral speed
• spike spacing
• grain fissuring
• grain breakage