harmful bacteria and fungi and excessive shrinkage. When air is forced through a bulk crop, it must travel through narrow paths between individual particles. Friction along air paths creates resistance to airflow. Fans must develop enough pressure to overcome this resistance and move air through the crop. Therefore, knowledge of the resistance to airflow through agricultural products is important in the design of drying, cooling, or aeration systems and fan selection for these systems. The resistance to airflow of grains and seeds is represented by pressure drops across unit depths of a column of the products. The pressure drop depends on a number of the product and environment factors such as airflow rate, bed depth, fill method, presence of foreign materials, moisture content and surface and shape characteristics of the products (Dairo and Ajibola, 1994; Agullo and Marenya, 2005).