Impacts of Soil Organic Carbon on Soil Physical Behavior

Abstract

Management-induced changes in soil organic carbon (SOC) concentration can affect soil physical behavior. Specifically, removal of crop residues as biofuel may thus adversely affect soil attributes by reducing SOC concentration as crop residues are the main source of SOC. Implications of crop residue management for soil erosion control, water conservation, nutrient cycling, and global C cycle have been discussed, but the potential impacts of residue removal-induced depletion of SOC on soil physical properties have not been widely studied. We reviewed published information on the relationships of SOC concentration with soil structural stability, consistency, compaction, soil water repellency, and hydraulic properties with emphasis on crop residue management. Our review indicates that studies specifically assessing relationships between crop residue management-induced changes in SOC concentration and soil physical properties are few. These studies indicate, however, that crop removal or addition can alter SOC concentration and concomitantly affect soil physical attributes with a magnitude depending on the amount of residue removed or returned, constituents of residue-derived SOC, tillage and cropping system, soil type, and climate. Our review also indicates that, in general, management practices that affect SOC concentration can directly influence soil physical properties. Decrease in SOC concentration reduces subcritical water repellency and aggregate stability and strength, increases soil's susceptibility to excessive compaction, and reduces macroporosity, hydraulic conductivity, and water retention. Soil organic matter improves soil physical properties by providing organic binding agents, inducing slight water repellency, lowering soil bulk density, and improving the elasticity and resilience of the whole soil. The numerous benefits of SOC on soil physical attributes suggest that SOC concentration should be maintained or increased through proper management practices. Indiscriminate residue removal for off-farm uses reduces SOC pools and can adversely affect soil and environment. Crop residues not only protect the soil surface from erosive forces but also maintain SOC concentration, which is essential to improve soil physical behavior and sustain soil productivity. Management practices including no-till with high residue input, continuous cropping systems, cover crops, and grass-based rotations should be promoted to further increase SOC concentration and thus improve soil physical behavior.