Total and permanganate-oxidizable organic carbon in the corn rooting zone of US Coastal Plain soils as affected by forage radish cover crops and N fertilizer

• Published in: Soil & tillage research Vol. 165; pp. 247 - 257
• Main Authors: Wang, Fang, Weil, Ray R., Nan, Xiongxiong
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.01.2017
• Subjects: autumn; Carbon; carbon nitrogen ratio; carbon sequestration; coastal plain soils; corn; corn silage; cover crops; Distribution; exudation; forage; Forage radish; nitrogen fertilizers; Permanganate oxidizable carbon; radishes; Raphanus sativus; rooting; soil depth; soil profiles; Subsoil; United States; United States; Forage radish; Subsoil; Permanganate oxidizable carbon; Carbon; Distribution
• ISSN: 0167-1987; 1879-3444
• DOI: 10.1016/j.still.2016.08.022

•Forge radish cover crops contribute a substantial amount of C to soil.•Forage radish significantly increased POXC and the ratio of POXC to TOC in both surface soil and subsoil.•There was a strong positive relationship between POXC and TOC overall.•POXC in 0–30cm was greater after radish than after no cover where N fertilizer was applied. Forage radish (Raphanus sativus L. var. longipinnatus) is a relatively new winter cover crop becoming widely grown in humid temperate North America. Little is known about how the use of this fall/winter cover crop may influence carbon sequestration and distribution in the soil profile in corn silage production system. The objectives of this study were to determine quantities and distribution in the soil profile of total organic carbon (TOC) and permanganate oxidizable carbon (POXC) as affected by forage radish cover crops and to examine the relationship between TOC and POXC in the profile. While there was no significant difference in TOC between radish (RAD) and no cover crop (NC) treatments for each depth interval at each site, the TOC in RAD (10.3gC/kg) was higher compared with NC (9.3gC/kg) in surface soil depth (0–30cm) when analyzed across all site years. Forage radish impacts on POXC were observed not only for surface horizons (0–15cm), but also for deep horizons (90–105cm). Banded nitrogen fertilizer affected the soil C:N ratio deep in the soil profile at both sites (at 90–105cm in RAD and at 60–75cm in NC). Where N fertilizer was applied, soil POXC in 0–30cm was significantly greater following radish (535.7mg POXC/kg) than following no cover crop (418.2mg POXC/kg). Additionally, strong positive linear relationships between POXC and TOC were observed (P<0.05), with a much steeper regression slope (higher POXC/TOC ratio) in the 60–105cm layer (POXC/TOC ratio=0.22) was much steeper than for the surface soil (0–30cm) with POXC/TOC ratio=0.05. We speculate that the higher POXC levels may have resulted from increased rooting and exudation by both corn and radish where nitrogen fertilizer was placed. Using forage radish cover crops show potential for mitigating against soil C depletion.