CORN ROOT DISTRIBUTION AS AFFECTED BY TILLAGE, WHEEL TRAFFIC, AND FERTILIZER PLACEMENT

Information concerning early-season corn (Zea mays L.) root distribution is needed so that fertilizer can be positioned to maximize root interception. The objective of this study was to examine corn root distribution as affected by tillage system, wheel traffic, and fertilizer placement. The study site was near Marshalltown, IA, on two silty clay loams, a Muscatine (fine-silty, mixed, mesic Aquic Hapludoll) and a Tama (fine-silty, mixed, mesic Typic Arguidoll). Three tillage systems (no-till, ridge-till, and chisel plow) with controlled traffic and two fertilizer-placement treatments (in-row and midpoint of the 76-cm interrow) were investigated. Root length, root weight, and root weight/length ratio were determined between 36 and 40 d after planting from 10-cm-diam. Soil core samples taken in rows and in interrow centers to a depth of 30 cm. Wheel-traffic compaction and fertilizer placement altered corn root distribution, regardless of tillage system. The upper 15 cm of interrows with wheel-traffic compaction had less than one-half the root length (1.27 km m-3) and root weight (19 g m-3) of untracked interrows (3.88 km m-3 and 49 g m-3, respectively). Root length and weight increased and root weight/length ratio decreased in either interrow or row positions when fertilizer was placed there. Placing fertilizer in an untracked interrow increased root length from 2.57 to 5.20 km m-3. Tillage system affected only root growth in untracked interrows. Because root growth in wheel tracks is restricted, fertilizer-use efficiency might be improved by not placing fertilizer in wheel tracks.