Data from: Cover crop root contributions to soil carbon in a no-till corn bioenergy cropping system

Crop residues are potential biofuel feedstocks, but residue removal may reduce soil carbon (C). The inclusion of a cover crop in a corn bioenergy system could provide additional biomass, mitigating the negative effects of residue removal by adding to stable soil C pools. In a no-till continuous corn bioenergy system in the northern US Corn Belt, we used 13CO2 pulse labeling to trace plant C from a winter rye (Secale cereale) cover crop into different soil C pools for 2 years following rye cover crop termination. Corn stover left as residue (30% of total stover) contributed 66, corn roots 57, rye shoots 61, rye roots 50, and rye rhizodeposits 25 g C m−2 to soil. Five months following cover crop termination, belowground cover crop inputs were three times more likely to remain in soil C pools than were aboveground inputs, and much of the root-derived C was in mineral-associated soil fractions. After 2 years, both above- and belowground inputs had declined substantially, indicating that the majority of both root and shoot inputs are eventually mineralized. Our results underscore the importance of cover crop roots vs. shoots and the importance of cover crop rhizodeposition (33% of total belowground cover crop C inputs) as a source of soil C. However, the eventual loss of most cover crop C from these soils indicates that cover crops will likely need to be included every year in rotations to accumulate soil C.作物残体（crop residues）是极具潜力的生物燃料原料（biofuel feedstocks），但残体移除可能会降低土壤碳（C）储量。在玉米生物能源系统中纳入覆盖作物（cover crop），可额外提供生物质，通过补充稳定土壤碳库，缓解残体移除带来的负面影响。针对美国北部玉米带的免耕连作玉米生物能源系统，本研究采用13CO2脉冲标记（13CO2 pulse labeling）技术，追踪冬黑麦（Secale cereale）覆盖作物的碳在覆盖作物翻压后的两年内，如何进入不同土壤碳库。留存为残体的玉米秸秆（占总秸秆量的30%）为土壤贡献了66 g C m−2，玉米根系贡献57 g C m−2，冬黑麦地上部贡献61 g C m−2，冬黑麦根系贡献50 g C m−2，冬黑麦根际沉积物（rhizodeposits）贡献25 g C m−2。覆盖作物翻压5个月后，地下部覆盖作物碳输入留存于土壤碳库的概率是地上部输入的三倍，且大部分根系来源的碳存在于矿质结合态土壤组分（mineral-associated soil fractions）中。两年后，地上部与地下部的碳输入均出现显著下降，表明根系与地上部来源的大部分碳最终均被矿化。本研究结果凸显了覆盖作物根系与地上部的碳输入差异，以及覆盖作物根际沉积（rhizodeposition）作为土壤碳来源的重要性，其贡献占地下部覆盖作物总碳输入的33%。但这类土壤中大部分覆盖作物碳最终会发生流失，这表明若要实现土壤碳积累，可能需要每年在轮作（rotations）中纳入覆盖作物。