Influence of soil temperature during root appearance on the trajectory of nodal roots of field grown maize

Trajectories of maize nodal roots were studied to test the hypothesis that roots which appear on a common internode have similar geometrical characteristics, and to assess the effect of soil temperature on root trajectory. Treatments consisted of three sowing dates, a comparison between mulched and non-mulched soil, a replication of one sowing date for two years in two locations, and a comparison between two cultivars at one sowing date. All these sources of variation, except the cultivar, had an appreciable effect on the trajectories of roots which appeared on the first four internodes. The horizontal component of the trajectory differed significantly between treatments, ranging from 93 to 700 mm in roots which appeared on the second internode, and from 71 to 569 for those on the third internode. The original hypothesis had, therefore, to be rejected. Mean soil temperature during the 100°C.days after root appearance accounted for the differences in trajectory between location, year, sowing date and mulch treatments, and for the differences between internodes within each location. The critical period during which temperature affected root trajectory probably began at root appearance, and ended between 50 and 100°C days after root appearance, i.e. when the root was less than 100 mm long.