Physical rice grain quality as affected by biophysical factors and pre-harvest practices

Varietal purity and proportions of grains with brown spots, fissured grains, chalky grains and whole grains in a rice sample are important grain quality attributes influencing consumer's preference and price but little information exist on how these grain quality attributes are affected by biophysical factors and pre-harvest practices. Several authors have studied in isolation the effect of biophysical factors and pre-harvest practices on rice grain quality but most of these studies neither looked at these within the context of agro-ecological zones nor production systems. The effects of agro-ecological zone (AEZ) (highlands, sub-humid, humid and semi-arid), production system (irrigated lowland, rain-fed lowland and rain-fed upland) and pre-harvest practices on grain quality attributes were investigated in 5 African countries using data collected through on-farm survey. The rice samples were generally characterized by low varietal purity, high proportion of brown spots, fissured and chalky grains and a low proportion of whole grains. Also, they had large variations across and within AEZs and production systems. AEZs and crop establishment method affected varietal purity. AEZ, production system affected chalkiness. AEZ and type of variety influenced percentage of grains with fissures. Percentage of whole grains were affected by AEZ, production system and weeding frequency. While grain quality attributes were strongly affected by biophysical factors, there is also room for improving grain quality through good pre-harvest practices.