Soil-root-canopy interactions

When supplies of water and mineral nutrients are adequate, crop growth is d etermined by the amount of solar radiation intercepted over the season and the efficiency of its conversion into dry matter. Soil factors such as drou ght, nutrient availability, salinity, waterlogging, mechanical impedance an d root-infecting pathogens can be a serious constraint to yield and operate through effects on the growth, photosynthetic activity and duration of the canopy, and on the partitioning of biomass to harvested parts. One approac h to overcome restrictions on the canopy and enhance yield is to modify roo t systems so that they are better suited to the prevailing soil conditions. This might be achieved through genetic improvement or by cultural practice s. A better understanding of the physiology of root systems is required to identify appropriate root traits for selection or management. Not only shou ld this encompass considerations of the function of roots in the capture of water and nutrients and the provision of anchorage, but also new concepts about the role of chemical signals in the regulation of the canopy. Greater emphasis must be placed on field-based research. The growth, development a nd activity of roots in the field can differ markedly from those in most la boratory experiments, because field soils are more complex in structure and differ in their biological, chemical and physical properties. It is argued that a decline in field-based research of crop root systems, as seen in th e UK over the last 15-20 years, could, if allowed to continue, generate a s kills gap which may undermine future exploitation of discoveries made at th e cell and molecular level.