Number of maize nodal roots as affected by plant density and nitrogen fertilization : relationships with shoot growth

Abstract

The effect of plant density and N fertilization rate on the number of maize nodal roots was studied. Maize, early maturing cultivar Dea, was grown for two years in Colmar, France, on a deep clay loam at two plant densities (8.5 and 14.4 plants m−2 in 1989 ; 9.0 and 12.4 plants m−2 in 1991) and two N fertilization rates (0 and 14 g m−2 of N).Thirty-six plants per treatment were sampled at six dates until silking, and at harvest. The number of visible and expanded leaves, the shoot biomass per plant and the number of nodal roots per phytomer were recorded. In 1991 the number of root primordia was also recorded.Results showed that shoot biomass per plant was significantly reduced at the higher densities and in the treatments without applied N. On upper phytomers (P6 to P8), there were fewer roots at the higher plant densities and in the treatments without applied N. This reduction was due to fewer root primordia actually elongating. There was a linear relationship between the number of roots on upper phytomers and the shoot growth rate of plants during root emergence on these phytomers. This confirms, in agreement with other results, that root emergence on these phytomers is trophically regulated.