Biofuel crops, including annuals such as maize (Zea mays L.), soybean [Glycine max (L.) Merr.], and canola (Brassica napus L.), as well as high-biomass perennial grasses such as miscanthus (Miscanthus × giganteus J.M. Greef & Deuter ex Hodkinson & Renvoiz), are candidates for sustainable alternative energy sources. However, large-scale conversion of croplands to perennial biofuel crops could have substantial impacts on regional water, nutrient, and C cycles due to the longer growing seasons and differences in rooting systems compared with most annual crops. However, due to the limited tools available to nondestructively study the spatiotemporal patterns of root water uptake in situ at field scales, these differences in crop water use are not well known. Geophysical imaging tools such as electrical resistivity (ER) reveal changes in water content in the soil profile. In this study, we demonstrate the use of a novel coupled hydrogeophysical approach with both time domain reflectometry soil water content and ER measurements to compare root water uptake and soil properties of an annual crop rotation with the perennial grass miscanthus, across three growing seasons (2009–2011) in southwest Michigan, USA. We estimated maximum root depths to be between 1.2 and 2.2 m, with the vertical distribution of roots being notably deeper in 2009 relative to 2010 and 2011, likely due to the drought conditions during that first year. Modeled cumulative ET of both crops was underestimated (2–34%) relative to estimates obtained from soil water drawdown in prior studies but was found to be greater in the perennial grass than the annual crops, despite shallower modeled rooting depths in 2010 and 2011.

中文翻译：

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通过耦合电阻率和土壤含水量测量揭示生物燃料作物的根系吸水量

生物燃料作物，包括一年生作物，如玉米 ( Zea mays L.)、大豆 [ Glycine max (L.) Merr.] 和油菜 ( Brassica napus L.)，以及高生物量多年生草类如芒草 ( Miscanthus ×巨人JM Greef & Deuter ex Hodkinson & Renvoiz) 是可持续替代能源的候选者。然而，与大多数一年生作物相比，由于生长季节较长和根系差异，将农田大规模转化为多年生生物燃料作物可能会对区域水、养分和碳循环产生重大影响。然而，由于可用于在田间尺度上无损地研究根系吸水的时空模式的工具有限，作物用水的这些差异尚不清楚。诸如电阻率 (ER) 之类的地球物理成像工具揭示了土壤剖面中含水量的变化。在这项研究中，我们展示了使用一种新颖的耦合水文地球物理方法，结合时域反射计土壤含水量和 ER 测量来比较一年生作物轮作与多年生芒草的根系吸水量和土壤特性，跨越三个生长季节（2009-2011）美国密歇根州西南部。我们估计最大根深在 1.2 到 2.2 m 之间，与 2010 和 2011 年相比，2009 年根的垂直分布明显更深，这可能是由于第一年的干旱条件。相对于先前研究中从土壤水分下降获得的估计值，两种作物的模拟累积 ET 被低估了 (2-34%)，但发现多年生草中的累积 ET 大于一年生作物，尽管 2010 和 2011 年模拟的生根深度较浅。