Winter camelina [Camelina sativa (L.) Crantz] and field pennycress [Thlaspi arvense L.] are oilseed feedstocks that can be employed as winter-hardy cover crops in the current cropping systems in the U.S. upper Midwest. In addition to provide multiple ecosystem services, they can be a further source of income for the farmer. However, using these cover crops is a new agricultural practice that has only been studied recently. The objective of this study was to assess and compare the environmental performance of a maize [Zea mays L.]-soybean [Glycine max (L.) Merr.] cropping system with different winter cover crops - camelina, pennycress, and rye (Secale cereale L.) - in the U.S. upper Midwest. Field experiments were carried out from 2016 to 2017 (2-year maize-soybean sequence) at three locations: Morris (Minnesota), Ames (Iowa), and Prosper (North Dakota). The environmental impact assessment was carried out using a “cradle-to-gate” life cycle assessment methodology. Four impact categories were assessed: global warming potential (GWP), eutrophication, soil erosion, and soil organic carbon (SOC) variation. Two functional units (FU) were selected: (1) 1 ha year⁻¹, and (2) $1 net margin. When expressed with the FU ha yr⁻¹, across the three locations cover crops had (a) lower eutrophication potential and water soil erosion, and (b) lower GWP if the cover crop was not fertilized with nitrogen. Camelina and pennycress were more effective than rye in reducing soil losses, while the three cover crops provided similar results for eutrophication potential. The results for the SOC variation were mixed, but the sequence with rye had the best performance at all locations. When expressed with the FU $ net margin, sequences including camelina and pennycress were overall the worst sequences in mitigating greenhouse gas emissions and nutrient and soil losses. This negative performance was mainly due to the seed yield reduction in the second year of the sequence for both the main cash crop (soybean) and the relayed-cover crop compared with the conventional sequence maize-soybean. Such result led to a lower net margin per hectare in the sequences including camelina and pennycress when compared with the control. The results of this study suggest that the introduction of camelina and pennycress as winter-hardy cover crops has a strong potential for reducing the environmental impacts of the maize-soybean rotation. However, a field management optimization of these cover crops in a relay-cropping system is needed to make them a sustainable agricultural practice.

冬季山茶花[ Camelina sativa（L.）Crantz]和田间小叶菊[ Thlaspi arvense L.]是油料原料，可以用作美国中西部中部当前种植系统中的耐寒作物。除了提供多种生态系统服务外，它们还可以成为农民的另一收入来源。但是，使用这些覆盖作物是一种新的农业实践，直到最近才进行了研究。这项研究的目的是评估和比较具有不同冬季覆盖作物的玉米[ Zea mays L。]-大豆[ Glycine max（L.）Merr。]种植系统-山茶花，豆科植物和黑麦（Secale）的环境表现。谷物L.）-在美国中西部。从2016年到2017年（玉米-大豆序列为2年）在三个地点进行了田间试验：莫里斯（明尼苏达州），艾姆斯（爱荷华州）和Prosper（北达科他州）。使用“从摇篮到大门”的生命周期评估方法进行了环境影响评估。评估了四个影响类别：全球变暖潜势（GWP），富营养化，土壤侵蚀和土壤有机碳（SOC）变化。选择了两个功能单元（FU）：( 1）年^-1公顷，和（2）$ 1的净利润。用FU ha yr ^-1表示，在这三个地方，覆盖作物（a）的富营养化潜力和水土流失较低，（b）如果覆盖作物未施氮，则GWP较低。在减少土壤流失方面，山茶和豆科植物比黑麦更有效，而三种覆盖作物的富营养化潜力相似。SOC变化的结果好坏参半，但是带有黑麦的序列在所有位置都具有最佳性能。当用FU $净利润表示时，包括山茶花和小豆瓣在内的序列总体上在减少温室气体排放以及养分和土壤流失方面是最差的序列。这种消极表现主要是由于与常规序列玉米-大豆相比，主要经济作物（大豆）和中转套作作物的第二年种子产量下降。与对照相比，这样的结果导致包括茶花和小豆瓣在内的序列的每公顷净利润降低。这项研究的结果表明，引入茶花和小豆瓣作为耐寒作物，具有减少玉米-大豆轮作对环境的影响的巨大潜力。但是，需要在套作系统中对这些覆盖作物进行田间管理优化，以使其成为可持续的农业实践。