Negative relationship between topsoil root production and grain yield in oat and barley

Production and maintenance of vegetative organs is costly for cereal crops, and thus it should be advantageous for crop production to produce no more roots and shoots than necessary to ensure maximum output. Excessive growth of vegetative organs may be genetically determined or triggered by resource deficiency or competition. While aboveground structures have received much attention from breeders, the same is not true of roots, which are not so readily observable. The purpose of this study was to examine the relationship between collective crop yield and vegetative growth parameters under favourable abiotic conditions in densely sown monocultures of oat and barley, with specific focus on root traits in the topsoil. A diverse set of existing varieties, as well as original crosses within both species were sown as monoculture patches in the field. Significant negative relationships were found between several root length-related traits and grain or protein yield in both species. Among oat crosses, we found a significant negative relationship between topsoil root length density and both grain and protein yield. In barley, the negative relationship between root length and yield was tied to shoot biomass - plants that grew longer roots per unit shoot biomass (root length ratio) produced lower grain yields. The results indicate that plants produced longer roots in the topsoil than necessary for maximum yield. While we cannot state with certainty the cause of the observed negative relationships between root growth and yield parameters, the results still suggest that root growth redundancy exists in cereals.