Hydrologic cost-effectiveness ratio favors switchgrass production on marginal croplands over existing grasslands

Abstract

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.

Estimating Field-Level Perennial Bioenergy Grass Biomass Yields Using the Normalized Difference Red-Edge Index and Linear Regression Analysis for Central Virginia, USA

“…Perennial grasses offer many ecosystem services, such as supporting wildlife habitats [1,2], moderating soil erosion [3][4][5], conserving water [6], and improving the soil and water quality [7,8]. Their abilities to produce a high biomass yield with a low fertilizer input and grow across many regions make perennial grasses an ideal bioenergy feedstock [9], playing a key role in the clean energy transition.…”

Response of Surface Runoff and Sediment to the Conversion of a Marginal Grassland to a Switchgrass (Panicum virgatum) Bioenergy Feedstock System

“…The most advanced micrometeorological method for the direct observation of the exchange of the water flux between the ecosystem and the atmosphere (eddy covariance technique) reported a higher peak and greater accumulated ET in the growing season for switchgrass than prairie [54], which indicates a potential reduction in the runoff with the conversion to switchgrass. A simulation that incorporated the switchgrass growth parameters and fertilizer application into the Soil and Water Assessment Tool, which is a prevailing hydrology model that is used to simulate the impact of the land use, the land management practices, and climate change on the water quality and quantity, from the small-watershed scale to the river-basin scale, suggests that switchgrass production on existing grassland would substantially reduce the streamflow (27.7%) at the subwatershed scale [55]. However, an increase in the ET during the growing season may not necessarily translate into a reduction in the total runoff since the runoff in this system occurs mainly before or after the growing season.…”

Assessment of Sweet Sorghum-Based Ethanol Potential in China within the Water–Energy–Food Nexus Framework

“…Recent studies showed that inappropriate development planning of biofuels may cause conflicts with water and food [14]. Increased biofuel demand would push up water use, and the low water efficiency of developing bio-ethanol on the marginal lands could aggravate water consumption [15][16][17]. Besides, planting energy crops on the cultivated lands may improve energy supply, but it also results in less cultivated lands for food planting and causes risks to food security [18].…”