Spatial Variability of Biofuel Production Potential and Hydrologic Fluxes of Land Use Change from Cotton (Gossypium hirsutum L.) to Alamo Switchgrass (Panicum virgatum L.) in the Texas High Plains

Abstract

Bioenergy crop production has the potential to protect marginal crop lands that generate high surface runoff and produce poor crop yields. Long-term evaluation of the impacts of such land use change on hydrologic fluxes and biofuel production potential is necessary before adopting such strategies on a large scale. In this study, the hydrologic impacts of replacing cotton (Gossypium hirsutum L.) on marginal lands in an intensive agricultural watershed in the Texas High Plains with Alamo switchgrass (Panicum virgatum L.) as a bioenergy crop were evaluated using the Agricultural Policy/ Environmental eXtender (APEX) model. The surface runoff to cotton yield ratio was used as a criterion to identify marginal cotton subareas (homogenous spatial units delineated by APEX) in the study watershed, and three replacement scenarios (low (9 %), medium (33 %), and high (57 %) extents of cotton acreage replaced by switchgrass) were implemented in the scenario analysis. The average (1994)(1995)(1996)(1997)(1998)(1999)(2000)(2001)(2002)(2003)(2004)(2005)(2006)(2007)(2008)(2009)) annual surface runoff decreased by about 84 and 66 %, and the percolation increased by 106 and 57 % in the irrigated and dryland subareas, respectively, when cotton was replaced by switchgrass under the high replacement scenario. Spatial analysis showed that switchgrass was a feasible bioenergy crop for replacing cotton, especially in the western part of the study watershed, due to its higher water use efficiency and better water conservation effects compared to cotton. It is estimated that 193 and 381 million liters of ethanol could be produced from the dryland and irrigated subareas of the study watershed, respectively, under the high replacement scenario.

Assessing the hydrologic and water quality impacts of biofuel‐induced changes in land use and management

“…More detailed information for the model setup can be found in Chen et al . (,b). For the HRU and subarea definitions, thresholds of 5%, 5%, and 10% were used for land use, soil type, and slope, respectively.…”

“…The APEX model was initially calibrated against observed streamflow and cotton lint yield data for the upstream subwatershed (Chen et al ., 2016b). As the observed N load data were not available for this upstream subwatershed, the APEX model was integrated with the SWAT model and the net flow, and sediment and nutrient loads from the upstream subwatershed were input as a point source to the downstream subwatershed at Gauge I (Fig.…”

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

“…Although there have been several hydrologic modeling studies on land use conversion to switchgrass production, few have considered conversion of only marginal lands (e.g. [ 16 , 17 ]). Currently, there is no widely accepted definition of marginal lands that would let us identify them on a map.…”

“…This complicates regional scale studies of bioenergy production and its relation with environmental variables. Previous researchers have used a variety of definitions for marginal lands including: lands that are susceptible to degradation and low inherent productivity, hence high risk for crop production [ 18 ]; lands that are less suitable for crop production due to inherent soil or climatic limitations or lands that are venerable to environmental risks [ 15 , 19 ]; abandoned agricultural lands and lands reserved for conservation, buffer strips along water bodies and roadway, and contaminated lands [ 20 ]; lands with a high runoff per unit cotton yield [ 17 ]; and lands having severe to very severe limitations for production of crops common to the area [ 21 ].…”