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 w ere grown in a glasshouse in large (120 x 10.5 x 5 cm) containers whic h allowed continuous observation of root growth and control of soil wa ter contents at all depths. In both species, drying of the topsoil res ulted 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 g rowth in the subsoil preceded the decrease in the topsoil. Drying of t he topsoil decreased shoot P concentrations in both species, whereas t he concentrations of N, K and Ca were not significantly affected despi te enriched fertilizer levels in the topsoil. In both species, after r ewetting, root growth in the topsoil rapidly recovered, and after 5 d exceeded that of the continuously irrigated plants. This increase of r oot growth in the topsoil occurred at the expense of root growth in th e subsoil. The results demonstrate that maize and rape plants may rapi dly respond to drying and rewetting the topsoil by locally increasing root growth in soil layers with the most favourable conditions. This p lasticity in root growth is a factor which contributes to the maintena nce of an adequate nutritional status.