|Zaman Hussain, Mir|
Submitted to: Journal of Geophysical Research-Biogeosciences
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/22/2013
Publication Date: 7/9/2013
Citation: Zeri, M., Zaman Hussain, M., Anderson-Teixeira, K.J., DeLucia, E.H., Bernacchi, C.J. 2013. Water use efficiency of perennial and annual bioenergy crops in central Illinois. Journal of Geophysical Research-Biogeosciences. 118(2):581-589. Interpretive Summary: Measurements of water use and carbon uptake by vegetation were measured over three growing seasons representing the establishment phase associated with perennial grasses. Similar measurements were made for the corn-soybean agroecosystem. The goal of these measurements were to determine how changing the landscape to accommodate bioenergy crops (the perennials) might influence the trade-offs between carbon and water. The annual and perennial ecosystems both had relatively high carbon uptake relative to water use, but the corn-soybean agroecosystem devoted a significant amount of that carbon into harvested yield while losing soil carbon. Since soil carbon is critical for long term sustainability, this suggests there might be less sustainability associated with annual crops. The perennial grasses in some cases, particularly after a year or two of growth, had high harvested material relative to water loss, but none of the perennial ecosystems were shown to lose carbon from the soil. These results suggest that long-term sustainability of land use change should include metrics that assess the long-term soil carbon accumulation as well as biomass harvested from the field.
Technical Abstract: Sustainable bioenergy production depends upon the efficiency with which crops use available water to produce biomass and store carbon belowground. Therefore, water use efficiency (WUE; productivity vs. annual evapotranspiration, ET) is a key metric of bioenergy crop performance. We evaluate WUE of three potential perennial grass bioenergy crops, Miscanthus × giganteus (miscanthus), Panicum virgatum (switchgrass), and an assemblage of prairie species (28 species), and Zea mays–Glycine max rotation, during the establishment phase in Illinois. Ecosystem WUE (EWUE; net ecosystem productivity vs. ET) was highest in miscanthus, reaching a maximum value of 12.8 ± 0.3 kg ha-1 mm-1 in the third year, followed by switchgrass (7.5 ± 0.3 kg ha-1 mm-1) and prairie (3.9 ± 0.3 kg ha-1 mm-1); the row crop was the lowest. EWUE was partitioned into harvest-WUE (HWUE, harvested biomass vs. ET) and net biome productivity-WUE (BWUE, calculated as NEP - harvest vs. ET). After three years of establishment HWUE and BWUE were highest in miscanthus (9.0 ± 2 and 3.8 ± 2.9 kg ha-1 mm-1, respectively) providing a net benefit to the carbon and water balances, while the row crops had a negative carbon balance and a negative BWUE. BWUE for maize/soybean indicate that this ecosystem would deplete the soil carbon stocks while using the most water resources. Switchgrass had the second highest BWUE, while prairie was almost neutral indicating that long-term carbon sequestration for this agro-ecosystem would be sensitive to harvest timing with an early harvest removing more biomass, and thus carbon, from the field.