Impacts of Hybrid Selection and Nitrogen Fertilization on Root-derived Carbon Inputs in Maize

Background and Aims Root-derived carbon (C) inputs are increasingly recognized as important precursors to soil organic carbon (SOC). However, the extent to which these inputs can be influenced by nitrogen (N) fertilizer management and plant stature remains poorly understood. This study investigated how N fertilization rate and maize hybrid stature trade off between above- and belowground performance, including investment in root traits, exudation, and soil microbial C pools. Methods Tall- and short-stature maize (Zea mays) hybrids, from Bayer’s breeding pipeline, were grown in a pot experiment in two soil matrices (sandy and loamy), with N fertilization rates of 0, 90, 180, and 270 kg N ha⁻¹. C pools in above- and belowground compartments were assessed, including root exudates, root biomass and length, soil microbial biomass C, and total soil C. Results Soil matrix and maize hybrids of different stature primarily explained differences in root exudation and belowground C inputs. Short-stature maize produced 22% greater dry root biomass than tall maize across N treatments. Loamy soils accumulated higher soil microbial biomass C and peaked at intermediate N rates, where fertilization achieved the greatest response in root biomass and C inputs. The highest N rates resulted in lower belowground C investment (particularly > 180 kg N ha⁻¹ in loamy soil). Conclusion Maize hybrid selection and N fertilization interact to shape root-derived C inputs and soil microbial biomass, with short-stature hybrids and moderate N rates enhancing belowground C allocation. These findings suggest that short-stature maize and avoiding excessive N fertilizer rates can promote root contributions to key soil C pools.