Maize and soybean root front velocity and maximum depth in Iowa, USA

•Maize and soybean roots occupy the space between 76cm rows at 480°Cd after sowing.•Root front velocity change rate from slow to fast at 5th maize leaf and 3rd soybean node.•Root front velocity ranged from 0.9cmd−1 (slow phase) to 3.2cmd−1 (fast phase).•Corn and soybean maximum root depth varied from 89 to 157cm.•Groundwater table depth explained 61% of the variation in maximum root depth.