Carbon flow through energycane agroecosystems established post-intensive agriculture

Authors: CROW, SUSAN - University Of Hawaii; WELLS, JON - University Of Hawaii; SIERRA, CARLOS - Max Planck Institute For Biogeochemistry; YOUKHANA, ADEL - University Of Hawaii; OGOSHI, RICHARD - University Of Hawaii; RICHARDSON, DANIEL - University Of Hawaii; GLAZER, CHRISTINE - University Of Hawaii; MEKI, MANYOWA - Texas A&M Agrilife; Kiniry, James

Submitted to: Global Change Biology Bioenergy
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/19/2020
Publication Date: 9/11/2020
Citation: Crow, S.E., Wells, J., Sierra, C.A., Youkhana, A.H., Ogoshi, R.M., Richardson, D., Glazer, C.T., Meki, M.N., Kiniry, J.R. 2020. Carbon flow through energycane agroecosystems established post-intensive agriculture. Global Change Biology Bioenergy. 12:806-817. https://doi.org/10.1111/gcbb.12713.
DOI: https://doi.org/10.1111/gcbb.12713

Interpretive Summary: Improved climate change mitigation for high-yielding tropical perennial C4 grasses, such as sugarcane, energycane, and napiergrass cultivated as a feedstock for bioenergy involves zero-tillage to increase sequestered carbon (C) in the soil. We measured and modeled above ground biomass and below ground biomass, root decay, and soil C accumulation. This allowed us to predict C flow from inputs to sequestration for grasses cultivated under conventional plant and zero-tillage systems in Hawaii. Napiergrass had significantly greater above ground biomass than energycane and sugarcane. Energycane had great below ground biomass than napiergrass and sugarcane. Root/total biomass was highest for energycane following harvest and the second-year growth of sugarcane. Sixty six percent of below ground biomass died following the energycane ratoon, compared to 11% and 41% in napiergrass and sugarcane. After four years, the surface layer C stock did not differ among the crops, but the C stock held in the deep soil profile was greatest for energycane. We estimate that the average time that C from fresh belowground inputs remains in the surface layer soil is 113 years. Root turnover following harvest is an important soil C input, in combination with other root-derived sources, and the relative contribution of each was crop-dependent. Energycane emerged as the strongest candidate for soil C sequestration due to allocation of resources to roots, root turnover, and accumulation of soil C that will persist for over a century.

Technical Abstract: In addition to fossil fuel offsets, zero-tillage management of high-yielding tropical perennial C4 grasses, such as sugarcane, energycane, and napiergrass cultivated as a feedstock for bioenergy production can sequester carbon (C) in soil for an even greater, sustained net climate change mitigation of the production system. We measured and modeled aboveground biomass (AGB), belowground biomass (BGB), root decay, and soil C accumulation to understand and predict C flow from inputs to sequestration for grasses cultivated under conventional plant and zero-tillage systems in Hawaii. Napiergrass had significantly greater AGB (47.73, Mg ha-1 yr-1) compared to energycane (40.78, Mg ha-1 yr-1) and sugarcane (39.13 Mg ha-1 yr-1), but energycane had the greatest BGB (4.63 Mg ha-1 yr-1) compared to napiergrass (3.82 Mg ha-1 yr-1) and sugarcane (3.83 Mg ha-1 yr-1). Root/total biomass was highest for energycane following harvest and the second-year growth of sugarcane (0.14 for both). 66% of total BGB died following the energycane ratoon, compared to 11% and 41% in napiergrass and sugarcane. After four years, the surface layer C stock did not differ among the crops, but the C stock held in the deep soil profile was greatest for energycane. Surface layer accumulation rates averaged 2.7 Mg C ha-1 yr-1 and deep soil averaged 11.4, 8.7, and 5.9 Mg C ha-1 yr-1 for energycane, napiergrass, and sugarcane respectively. We estimate that the average time that C from fresh belowground inputs remains in the surface layer soil was 113 years. Root turnover following harvest is an important soil C input, in combination with other root-derived sources, and the relative contribution of each was crop-dependent. Energycane emerged as the strongest candidate for soil C sequestration due to allocation of resources to roots, root turnover, and accumulation of soil C that will persist for over a century.