Larger Field than Variety Effect on Belowground Maize Biomass and Root System Architecture

Analysis of multiple field experiments has proven that belowground biomass contributes twice more than aboveground biomass to build-up of soil organic matter (SOM). Alongside, a consensus has emerged that model based predictions are particularly ill-parameterized for amount and degradability of belowground biomass. Root system architecture (RSA) affects uptake of nutrients and water from the soil, thus determining crop performance. However, the changes of RSA in response to soil properties are poorly understood. Our objective was to evaluate the effects of maize variety versus field characteristics on RSA. Eight commercial maize varieties were grown in three experimental trials in North Belgium with different soil texture according to common agricultural practice. Undisturbed soil blocks (10×30×30cm³) with the intact topsoil rooting systems were collected at harvest time. Roots were washed, sieved, weighed and C, N and biochemical component content was measured. Root traits were quantified by 2D and 3D analysis. For 2D analysis, images of dried roots were analyzed by the software of “Root Estimator for Shovelomic Traits”. X-ray µCT was used on intact soil blocks (10×20×20cm³) to perform a detailed 3D model to capture the root-soil interface in situ. A novel segmentation procedure had to be developed to differentiate maize rooting systems from pre-processed CT-volumes as existing software failed to do so. First results indicated that only field impacted belowground biomass although both maize variety and field significantly affected aboveground biomass. Field also significantly influenced convex hull area and depth of rooting systems assessed on 2D images, and convex hull volume, depth, total volume and root diameter distribution in the 3D model. No significant variety effect on root traits could be observed, in neither 2D nor 3D models. Therefore, maize root biomass and RSA to some extent depend on field characteristics and is not necessarily in line with aboveground biomass.