Date of Award

8-2025

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Plant and Environmental Science

Committee Chair/Advisor

Dr. Rongzhong Ye

Committee Member

Dr. Vidya Suseela

Committee Member

Dr. William Bridges

Committee Member

Dr. Carl Trettin

Abstract

Historic intensive cultivation, in addition to the warm and humid climate, has resulted in low soil organic carbon (SOC) and nitrogen (N) concentrations in the southeastern U.S. Coastal Plain soils. Restoring SOC is key to ensuring sustainable production in these soils. This study aimed to evaluate cover cropping as a management strategy to improve soil C and N in this region. Specifically, it investigated how cover crops contribute to SOC stabilization and N availability in the form of living plants and dead residues. Three cover crops (cereal rye, hairy vetch, crimson clover) were tested in the field and laboratory incubations, either individually or in a mixture. The distribution, transformation and fates of root-derived (Chapters 2 and 4.2) and residue-derived C and N (Chapters 3 and 4.1) were quantified along with the soil C and N stocks in the soil profile (Chapter 5). Root-derived C was a significant source of SOC. Notably, cereal rye contributed relatively more assimilated C to subsoil (15-30 cm), whereas hairy vetch retained a greater portion in the topsoil (0-15cm), reflecting species-specific differences in belowground C distribution. Following termination, cover crop residue decomposition was largely governed by their C-to-N ratio and air temperatures, with legumes being decomposed more rapidly. Incorporations of vetch residues and their mixture with cereal rye reduced microbial decomposition of the native SOC but did not stimulate cumulative CO2 and N2O emissions during the main crop seasons. However, such impacts can be modified by mineral N additions, in which N addition enhanced N2O emissions when added together with cover crop residues. Despite their significant contributions to soil C dynamics, integrating various winter cover crops for six years did not increase total soil C and N stocks at one meter depth. However, when integrated with conservation tillage, they did promote C accumulation in the topsoil (0-15 cm) but caused C depletion in the subsurface. This study highlights the importance of complementary management practices to cover cropping in restoring SOC in sandy soils to enhance its productivity and sustainability.

Author ORCID Identifier

0000-0002-8115-2297

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