Deepening Root Inputs: Potential Soil Carbon Accrual From Breeding for Deeper Rooted Maize

Area of Science:

• Agricultural Science
• Soil Science
• Climate Change Mitigation

Background:

• Enhancing root depth and biomass in annual crops is a strategy to increase soil organic carbon (SOC) for climate mitigation and soil health.
• Maize, a high-acreage crop, has shallow roots, presenting an opportunity for genetic improvement.
• Understanding the SOC accrual potential from improved root phenotypes is currently lacking.

Purpose of the Study:

• To quantify the formation and composition of new SOC from maize root and exudate decomposition.
• To simulate the SOC accrual potential of maize ideotypes with enhanced root depth or biomass.
• To assess the scalability and impact of root-based breeding strategies for SOC sequestration in maize.

Main Methods:

• A 2-year field experiment using isotopically labeled maize roots and exudates to track SOC formation and composition (POM, chaOM, MAOM) down to 90 cm.
• Utilized the process-based MEMS 2 model to simulate SOC accrual from hypothetical maize root ideotypes.
• Compared breeding-based root improvements against established crop management practices for SOC accrual.

Main Results:

• Maize root decomposition preferentially formed particulate organic matter (POM), with higher efficiency below 50 cm.
• Root exudates preferentially formed mineral-associated organic matter (MAOM).
• Simulated deeper roots or increased root biomass yielded modest SOC increases (0.05–0.15 Mg C ha⁻¹ yr⁻¹), at the lower end of management practice estimates.

Conclusions:

• Breeding maize for increased root inputs has a limited per-hectare impact on SOC accrual.
• Significant SOC accrual and greenhouse gas reduction in maize-soy systems require broader cropping system changes.
• The study provides a framework for quantifying and forecasting SOC changes driven by crop root input modifications.