Our study objectives were to quantify genetic gains (GG) in yield plus macronutrient (S, P, K, Ca, Mg) and micronutrient (B, Mg, Zn, Mn, Fe, Cu, Al) contents, and investigate the relationship between harvest index (HI), nitrogen harvest index (NHI), and nutrient HI (NutHI) at physiological maturity in Bayer Crop Science legacy hybrids. Grain nutrients were analyzed in 38 maize hybrids, released between 1983 and 2020 in the US Corn Belt with nearly identical maturity groups. Yield was measured in all hybrids at two locations (Jerseyville, Illinois, and Lebanon, Indiana), while aboveground biomass was measured in a subset of 23 hybrids in 2021, representing both old and modern hybrids. The study spanned two years (2021 and 2022) and two N rates (45 kg N ha^-1 as Low-N in both years, and 205 and 246 kg N ha^-1 in 2021 and 2022, respectively, as High-N). A split-plot design was used, with main plots assigned to N rates and subplots to hybrids. While occasional increases in grain nutrient concentrations under Low-N compared to High-N (e.g., P and K) were observed, these did not alter the overall trends of increasing nutrient content due to yield improvements, plus consistently higher nutrient contents removed at High-N vs Low-N. Average NutHI at High-N was improved for P and Fe, but was lower for Zn, Mn and Cu. Relationships of NutHI to NHI were consistently negative at High-N, but neutral to positive for all nutrients except Fe at Low-N levels. Although increasing maize NHI is a desirable outcome in terms of N fertilizer balance, genetic gains in NHI were generally accompanied by lower NutHI at High-N and little to zero NutHI gain for nutrients other than N at Low-N.

Intensive agriculture has depleted soil carbon (C) stocks globally, necessitating a deeper understanding of soil organic carbon (SOC) formation to develop effective management strategies to rebuild soil carbon losses. Recent advancements in soil science suggest that simple-structured carbon compounds, such as plant root exudates or microbial necromass, may serve as the primary precursors of SOC. Therefore, management strategies aimed at enhancing SOC should focus on promoting the formation of these LMW C compounds. This study examines how corn hybrids (Bayer tall-statured and short-statured), soil types (sandy and loamy), and nitrogen fertilization rates (0, 90, 180, 270 kg N/ha) influence root exudation, belowground C inputs, and soil C pools in a greenhouse setting. By assessing C allocation between above- and belowground plant components, root exudation, and soil C pools (soil microbial biomass C and total soil C), we aim to optimize management practices for enhancing soil carbon storage. Results indicated that soil type and corn hybrid primarily drive root exudation and belowground C inputs, while nitrogen fertilization effects vary based on soil conditions. Additionally, short-statured corn contributed more to root development, averaging 22% greater dry root biomass across N fertilization treatments. The root biomass of corn grown in loamy soils exhibited a threshold where excessive nitrogen hindered root growth. Above all, these findings highlight that plant belowground C inputs are dependent on soil type and can be influenced by management decisions, like N fertilization and hybrid selection.

Corn (Zea mays L.) is a commonly grown crop with high nitrogen (N) demand. Modern hybrids and intensive fertilization practices have increased yields but may have compromised below-ground traits, such as root growth and biological soil health. Newly introduced short-stature corn hybrids are recognized for their lodging resistance; however, limited information is available regarding their belowground benefits. This study aimed to investigate how fertilization rates affect the belowground performance of short-stature corn compared to conventional tall-stature corn hybrids. Field experiments were conducted at two locations in Indiana, encompassing two contrasting corn statures and four nitrogen (N) rates (0, 100, 200, and 300 kg/ha). Root and soil samples were collected at a depth of 0-120 cm during the corn R2 growth stage using a hydraulic Giddings probe, followed by scanning and image analysis to quantify both belowground and aboveground biomass. Root biomass and length in short-stature corn were 1.35 and 1.42 times higher, respectively, compared to tall-stature corn, with greater differences observed in soils with higher organic matter content. Across both soil types, root biomass and length peaked at 200 kg/ha of nitrogen, with the majority concentrated in the top 30 cm layer. Soil microbial biomass, POXC, and PMC levels increased in high-organic-matter soil, but were unaffected by corn hybrids and nitrogen addition. This study demonstrates that short-stature corn hybrids exhibit enhanced root biomass and length, particularly under optimal N fertilization, while soil biological indicators are largely unaffected by hybrid type or N rate. Therefore, these findings emphasize the importance of optimizing nitrogen rates with short-stature hybrids to enhance root traits and soil health, guiding sustainable crop management decisions.

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.