Yimam Yohannes Tadesse, Ochsner Tyson E, Fox Garey A
Department of Soil and Crop Sciences, Texas A&M University, College Station, Texas, United States of America.
Department of Plant and Soil Sciences, Oklahoma State University, Stillwater, Oklahoma, United States of America.
PLoS One. 2017 Aug 8;12(8):e0181924. doi: 10.1371/journal.pone.0181924. eCollection 2017.
Switchgrass (Panicum virgatum L.) has attracted attention as a promising second generation biofuel feedstock. Both existing grasslands and marginal croplands have been suggested as targets for conversion to switchgrass, but the resulting production potentials and hydrologic impacts are not clear. The objectives of this study were to model switchgrass production on existing grasslands (scenario-I) and on marginal croplands that have severe to very severe limitations for crop production (scenario-II) and to evaluate the effects on evapotranspiration (ET) and streamflow. The Soil and Water Assessment Tool (SWAT) was applied to the 1063 km2 Skeleton Creek watershed in north-central Oklahoma, a watershed dominated by grasslands (35%) and winter wheat cropland (47%). The simulated average annual yield (2002-2011) for rainfed Alamo switchgrass for both scenarios was 12 Mg ha-1. Yield varied spatially under scenario-I from 6.1 to 15.3 Mg ha-1, while under scenario-II the range was from 8.2 to 13.8 Mg ha-1. Comparison of average annual ET and streamflow between the baseline simulation (existing land use) and scenario-I showed that scenario-I had 5.6% (37 mm) higher average annual ET and 27.7% lower streamflow, representing a 40.7 million m3 yr-1 streamflow reduction. Compared to the baseline, scenario-II had only 0.5% higher ET and 3.2% lower streamflow, but some monthly impacts were larger. In this watershed, the water yield reduction per ton of biomass production (i.e. hydrologic cost-effectiveness ratio) was more than 5X greater under scenario-I than under scenario-II. These results suggest that, from a hydrologic perspective, it may be preferable to convert marginal cropland to switchgrass production rather than converting existing grasslands.
柳枝稷（Panicum virgatum L.）作为一种很有前景的第二代生物燃料原料已受到关注。现有草地和边际农田都被提议作为转化为柳枝稷的目标，但由此产生的生产潜力和水文影响尚不清楚。本研究的目的是对现有草地（情景I）和对作物生产有严重到非常严重限制的边际农田（情景II）上的柳枝稷产量进行建模，并评估对蒸散量（ET）和径流的影响。土壤和水资源评估工具（SWAT）被应用于俄克拉荷马州中北部面积为1063平方公里的骷髅溪流域，该流域以草地（35%）和冬小麦农田（47%）为主。两种情景下，雨养阿拉莫柳枝稷的模拟年均产量（2002 - 2011年）均为12 Mg ha-1。在情景I下，产量在空间上变化范围为6.1至15. Mg ha-1，而在情景II下，范围为8.2至13.8 Mg ha-1。基线模拟（现有土地利用）与情景I之间的年均ET和径流比较表明，情景I的年均ET高5.6%（37毫米），径流低27.7%，径流减少量达4070万立方米/年。与基线相比，情景II的ET仅高0.5%，径流低3.2%，但一些月份的影响更大。在该流域，情景I下每吨生物质生产的产水量减少量（即水文成本效益比）比情景II大5倍以上。这些结果表明，从水文角度看，将边际农田转化为柳枝稷生产可能比转化现有草地更可取。
