Evapotranspiration partitioning and water use efficiency of switchgrass and biomass sorghum managed for biofuel

Abstract

Switchgrass (Panicum virgatum L.) and biomass sorghum (Sorghum bicolor L. Moench) are two candidate bioenergy crops for the US Southern Great Plains region. In this water-limited region, there is a need to partition evapotranspiration (ET) and to determine the water use efficiency (WUE) of these potential feedstocks. Both crops were grown in a field plot experiment at Stillwater, OK. Soil water content measurements were made by neutron probe every two weeks to a depth of 2.0 m in 0.2-m intervals over the course of three growing seasons. Growing season ET was estimated as the difference between growing season precipitation and change in root zone soil water storage. Evapotranspiration was partitioned by measuring canopy interception using interception trays and estimating soil evaporation using the FAO-56 dual crop coefficient method. Transpiration was calculated as ET minus soil evaporation and canopy interception. Transpiration was the largest component of ET; however, soil evaporation and canopy interception accounted for 28% of growing season ET for switchgrass and 42% for biomass sorghum. Although the non-productive losses were greater from biomass sorghum, WUE values of 9-49 kg ha-1 mm-1 based on ET and 22-83 kg ha-1 mm-1 based on transpiration were observed for biomass sorghum, which were greater than the WUE values of switchgrass, 8-21 kg ha-1 mm-1 based on ET and 12-28 kg ha-1 mm-1 based on transpiration. These results demonstrate that biomass sorghum is a candidate feedstock with potential to achieve greater WUE than switchgrass at this location; however, other factors such as economics and ecosystem services should also be considered.

Biomass sorghum and maize have similar water-use-efficiency under non-drought conditions in the rain-fed Midwest U.S.

“…Our biomass sorghum WUE observations (3.1-3.8 g kg -1 ) were similar to the average WUE for rain-fed biomass sorghum available in the literature (3.8 g kg -1 ; Hao et al, 2014;Yimam et al, 2015). For irrigated systems, our biomass sorghum WUE results are comparable to literature values (3.9 g kg -1 ; Garofalo & Rinaldi, 2013;Hao et al, 2014;Oikawa et al, 2014).…”

“…Our total ET estimates for biomass sorghum (614-618 mm) are comparable to reports for rain-fed biomass sorghum grown in Oklahoma (446-683 mm; Yimam et al, 2015). However, we found greater total ET than Hao et al (2014) who used a soil water content approach for irrigated biomass sorghum in Texas (227-517 mm).…”

“…Sweet sorghum was found to be less sensitive to drought than maize (Zegada-Lizarazu et al, 2012), and more water-useefficient than maize and other major grain crops (Steduto et al,1997;Katerji & Mastrorilli, 2014). However, previous studies on sorghum water dynamics have largely focused on grainyielding varieties (Steduto & Albrizio, 2005;Farré & Faci, 2006) and biomass sorghum in irrigated systems (Steduto et al, 1997;Farré & Faci, 2006;Rinaldi & Garofalo, 2013;Narayanan et al, 2013;Mullet et al, 2014;Hao et al, 2014Oikawa et al, 2014Yimam et al, 2015).…”

“…For biomass sorghum, the average WUE for irrigated studies was 4.1 g kg -1 while the mean WUE for rain-fed systems was 3.6 g kg -1 . Reports on the WUE of biomass sorghum in rain-fed environments are scarce (Yimam et al, 2015). To address this gap we established an experiment in the rain-fed, Midwest, US, in which we compared the WUE of biomass sorghum to maize, the dominant bioethanol feedstock in the region.…”

“…Consequently, data are limited for sorghum grown specifically for biomass production in rainfed systems (Yimam et al, 2015).…”