Management Protocols for Soil Carbon Sequestration

Conservation tillage (CT) and cover cropping are sustainable agricultural practices that may provide solutions for California’s declining environmental quality. This study investigates how CT and cover cropping affect soil organic matter dynamics in a cotton-tomato (Gossypium hirsutum, Lycopersicon esculentum) rotation in California’s San Joaquin Valley. After five years of treatments, the top 30 cm of soil in the CT with CC system had 4,500 kg C ha-1 more C, while C increased by 3,800 kg C ha-1 in standard tillage with cover crop. In CT, the increase occurred in the surface 15 cm; while in standard tillage, it was distributed throughout the top 30 cm. In the treatments without cover crops, soil C was unchanged in the 0-30 cm depth. To refine our understanding of aggregate-protected C dynamics in CT systems, we labeled cotton with 13C in the field and followed the decomposition of both the roots and the shoots through three physical fractions: light fraction (LF) which tends to turnover quickly and two relatively stable C pools: intra-aggregate LF (iLF) and mineral-associated C (m). CT treatments retained more of the cotton residue-derived C in LF and iLF initially. However, these differences disappear after a year of residue decomposition in the field. During the study, more shoot C was retained an