Maize root biomass and architecture depend on site but not on variety : consequences for prediction of C inputs and spread in topsoil based on root-to-shoot ratios

Knowledge about the response of root biomass and root system architecture (RSA) to soil conditions would increase efficiency in selecting high performance crop varieties and predicting the impact of rotations on long-term soil organic matter (SOM) stock. We evaluated the effect of variety and site on maize (Zea mays L.) root growth. Two-dimensional (2D) and 3D techniques were used to quantify changes of RSA. Commercial maize varieties were grown in three sites with typical soil types for maize cultivation in Belgium. We observed that at Merelbeke, above- and belowground biomass and root-to-shoot ratios (R/S) were larger compared to those at Ravels. Both factors interactively influenced an index of biological stability (ISB) based on biochemical quality of the roots. There were also more fine roots at Merelbeke than at Bassevelde and Ravels. Together with a lower ISB value, this suggests that site had an inherent effect on root biochemical quality. We conclude that a strong impact of site exists on both above- and belowground biomass; however, they are not necessarily correlated. With a fixed R/S, predictions of root biomass were misestimated in one half of the cases. This complex response of root phenotyping to varying soil conditions should not be overlooked