Response of the root system of a winter wheat crop to waterlogging

This study was aimed at analysing and quantifying the response of the root system dynamics of a wheat crop to waterlogging. Two experiments were carried out in parallel: one under controlled conditions with semi-permanent water tables using lysimeters equipped with oxygen measurers, and the other under conditions of artificially drained plots by continually monitoring their hydraulic functioning. The root system was observed frequently using the root mapping method, and this made it possible to measure the growth of the root front, to estimate root densities, and infer growth indices from them. The results showed that the anoxic medium for wheat roots consisted of a water-saturated soil with an oxygen concentration of below a critical threshold estimated to be 0.12 mol m(-)3 water. The results also showed that the area which was unfavourable to root growth corresponded to the water table topped with a capillary zone of approximately 6 cm. Once the critical threshold had been reached, it was the water-table duration that explained root behaviour and the first effects were perceptible after approximately 48 h. On the basis of these results, two stress variables were analysed: water-table duration in the root zone (WTD) and proportion of roots in the water table (RPWT). The RPWT variable gave the best results within the two experimental contexts. In the case of the permanent regime, this variable made it possible to consider the root proliferation observations made above the saturated zone. Equations linking the stress variable RPWT to the growth indices are proposed that offer new perspectives to modelling waterlogging effects.