Recent advancement in soil carbon research indicate that simple-structured, low-molecular-weight carbon (C) compounds, such as plant root exudates or microbial necromass, may serve as the primary precursors of soil organic carbon (SOC). The “surplus plant C theory” suggests that mild nutrient deficiency may stimulate plants to exude more C. However, there is no empirical evidence on whether the “surplus C” can be generated through N fertilization management thus enhancing soil C building. In this study, we aim to investigate how varying nitrogen (N) fertilizer rates affect root exudation quantity and other belowground C inputs, as well as the soil and microbial C pools in a greenhouse study. Different corn hybrids (short and tall statures) are planted in two field soil mixes that represent a high organic matter (OM) soil and low OM, sandy soil under proportional N rate increments (0, 80, 160, and 240 lbs N/acre). Our measurement protocol consists of the following steps: at the V8 growth stage, root exudates are collected both using the (1) pot leaching and (2) hydroponics-hybrid methods and measured by a Shimadzu TOC analyzer. Additionally, root, soil, and microbial parameters are recorded to determine the impact of treatments on belowground parameters and ecological processes. The results of this study will give insight into how plant-soil-microbial interactions respond to N fertilization management and can be managed to enhance soil C building and long-term agroecosystem sustainability.