EFFECT OF DRYING AND REWETTING THE TOPSOIL ON ROOT-GROWTH OF MAIZE AND RAPE IN DIFFERENT SOIL DEPTHS

The aim of the present experiments was to determine how fast maize and rape plants respond to drying and subsequent rewetting of the topsoil by changing their rooting patterns in different soil depths. Plants were grown in a glasshouse in large (120 x 10.5 x 5 cm) containers which allowed continuous observation of root growth and control of soil water contents at all depths. In both species, drying of the topsoil resulted in a rapid (after 6 d) decrease of root growth in the topsoil (0-40 cm) and an increase in the subsoil (80-120 cm). Increase of root growth in the subsoil preceded the decrease in the topsoil. Drying of the topsoil decreased shoot P concentrations in both species, whereas the concentrations of N, K and Ca were not significantly affected despite enriched fertilizer levels in the topsoil. In both species, after rewetting, root growth in the topsoil rapidly recovered, and after 5 d exceeded that of the continuously irrigated plants. This increase of root growth in the topsoil occurred at the expense of root growth in the subsoil. The results demonstrate that maize and rape plants may rapidly respond to drying and rewetting the topsoil by locally increasing root growth in soil layers with the most favourable conditions. This plasticity in root growth is a factor which contributes to the maintenance of an adequate nutritional status.