What is the role of soil organic carbon in carbon sequestration on rangelands, and what practices help increase SOC?

• A. Soil Organic Carbon stores atmospheric carbon; practices include rest-rotation grazing, perennial forage systems, residue retention, reduced disturbance, and diverse species.
• B. Soil Organic Carbon releases atmospheric carbon; practices include heavy tillage.
• C. SOC only accumulates in forests.
• D. SOC decreases with residue retention.

Answer: (A)

Soil organic carbon serves as a major store of carbon that has been drawn down from the atmosphere into the soil as plant residues and root material decompose and become part of soil organic matter. On rangelands, increasing this carbon storage strengthens the soil’s structure, fertility, and resilience while contributing to climate change mitigation.

The listed practices boost SOC in several linked ways. Rest-rotation grazing reduces continuous, intense disturbance, allowing plants to grow more and produce more litter and roots. That additional plant material becomes soil organic matter, feeding soil microbes and contributing to a thicker, more stable carbon pool, while less compaction preserves soil pores for water and air, supporting biological activity that builds SOC.

Perennial forage systems provide consistent, year-round root networks and above-ground growth. Deep or persistent roots deposit carbon deeper in the soil profile and over longer periods, creating continuous inputs to the soil organic carbon pool and enhancing its persistence.

Residue retention means leaving plant leftovers on the ground rather than removing them. This surface cover protects soil from erosion, moderates temperature and moisture, and supplies substrates for microbial processing, all of which help convert plant residues into stable soil organic carbon rather than rapid loss.

Reducing disturbance, especially avoiding frequent tillage, slows the breakdown (mineralization) of existing soil organic carbon. With less soil turning and aeration, carbon remains in the soil longer and contributes to a larger SOC pool.

Diversity in plant species enhances both above- and below-ground biomass, increasing the quantity and diversity of carbon inputs through roots and litter. Different species also improve soil structure and microbial communities, supporting slower decomposition and greater SOC stabilization.

Together, these practices create a system where carbon inputs exceed losses, leading to greater soil organic carbon and enhanced sequestration on rangelands.