Nitrogen (N) fertilization affects bioenergy crop growth and productivity and consequently carbon (C) and N contents in soil, it however remains unclear whether N fertilization and crop type individually or interactively influence soil organic carbon (SOC) and total N (TN). In a three-year long fertilization experiment in switchgrass (SG: Panicum virgatum L.) and gamagrass (GG: Tripsacum dactyloides L.) croplands in Middle Tennessee USA, soil samples (0–15cm) were collected in plots with no N input (NN), low N input (LN: 84 kg N ha^-1 yr^-1 in urea) and high N input (HN: 168 kg N ha^-1 yr^-1 in urea). Besides SOC and TN, the aboveground plant biomass was also quantified. In addition to a summary of published root morphology data based on a separated mesocosm experiment, the root leachable dissolved organic matter (DOM) of both crops was also measured using archived samples. Results showed no significant interaction of N fertilization and crop type on SOC, TN or plant aboveground biomass (ABG). Relative to NN, HN (not LN) significantly increased SOC and TN in both crops. Though SG showed a 15–68% significantly higher ABG than GG, GG showed a 9.3–12% significantly higher SOC and TN than SG. The positive linear relationships of SOC or TN with ABG were identified for SG. However, GG showed structurally more complex and less readily decomposed root DOM, a larger root volume, total root length and surface area than SG. Collectively, these suggested that intensive N fertilization could increase C and N stocks in bioenergy cropland soils but these effects may be more likely mediated by the aboveground biomass in SG and root chemistry and morphology in GG. Future studies are expected to examine the root characteristics in different bioenergy croplands under the field fertilization experiment.

氮（N）的施肥会影响生物能源作物的生长和生产力，从而影响土壤中的碳（C）和氮的含量，但是尚不清楚氮的施肥和作物类型是单独还是相互作用影响土壤有机碳（SOC）和总氮（TN）。在美国田纳西州中部的柳枝（（SG：Panicum virgatum L.）和gamagrass（GG：Tripsacum dactyloides L.）农田中进行了为期三年的施肥实验，在无氮输入的样地中收集了土壤样品（0-15厘米）（ NN），低氮输入（LN：尿素中84 kg N ha ^-1 yr ^-1）和高氮输入（HN：168 kg N ha ^-1 yr ^-1在尿素中）。除了SOC和TN，还对地上植物生物量进行了定量。除了基于单独的中观试验公开的根系形态数据摘要外，还使用存档的样品测量了两种作物的根系可浸出可溶性有机物（DOM）。结果表明，氮肥和作物类型对SOC，TN或植物地上生物量（ABG）无显着影响。相对于NN，HN（非LN）显着增加了两种作物的SOC和TN。尽管SG的ABG比GG高15–68％，但是GG的SOC和TN比SG高9.3–12％。确定了SG的SOC或TN与ABG的正线性关系。然而，与SG相比，GG的结构更复杂，根DOM较不易分解，具有更大的根体积，总根长和表面积。总的来说，这些结果表明，强化氮肥可以增加生物能源农田土壤中的碳和氮储量，但这些影响可能更可能是由SG中的地上生物量以及GG的根系化学和形态引起的。预计未来的研究将在田间施肥试验下研究不同生物能源耕地的根系特征。