Investigations into the root:shoot relationship of sugarcane, and some implications for crop productivity in the presence of sub-optimal soil conditions

The relationship between root and shoot growth of sugarcane was studied under nonlimiting conditions, and also using experimental treatments that reduced the growth and effectiveness of the root system. A simple generic relationship was seen between the pattern of above and below ground growth under favourable conditions, with the root:shoot ratio of all varieties declining through ontogeny. When root pruning or defoliation treatments were imposed to alter this relationship, there was a change in the relative growth of the roots and shoot towards the re-establishment of the original trend in root:shoot ratio development. A similar response was seen when half the root-zone was allowed to dry down, with an increase in root growth relative to shoot growth suggesting a re-establishment of the equilibrium between the root system and shoot. The apparently conservative nature of the root:shoot relationship was further demonstrated by the growth response of sugarcane plants to restricted rooting volume. In this study, physically limiting root growth significantly reduced total plant weights, but did not influence biomass partitioning between the roots and shoot. These findings are consistent with existing models of root:shoot relations, and suggest that shoot growth is directly related to the functional capacity of the root system.