Sustainability of bioenergy crops: effects of long-term perennial grass cultivation on soil carbon storage
Abstract
Soil health and responsible management practices are critical to continued productivity and environmental protection in the intensively farmed American Midwest. Annually, over 90 million acres of farmland are dedicated to corn agriculture, of which 40% is ultimately converted to bioethanol. Alternative feedstocks for bioethanol, primarily large perennial grasses, represent a small but growing percentage of American farmland. In 2008, three perennial bioenergy crops, Miscanthus x giganteus (miscanthus), Panicum virgatum (switchgrass), and a 28-species prairie mixture were planted in converted corn fields in central Illinois. DayCENT modeling predicted that perennial grasses would be ecologically beneficial, increasing soil organic carbon (SOC) while producing a high-yielding biofuel crop. After establishment, perennials were maintained without pesticide, and with low-or-no fertilization. Crops were untilled, preserving the bank of belowground carbon created by the large rhizospheres of perennial plants. Aboveground biomass was harvested annually, with the highest yield in miscanthus, followed by switchgrass and prairie. After 8 years, significant increases (p<0.05) in SOC were measured in the surface soil (0-10 cm) of all perennials and in the deeper soil (0-30 cm) of miscanthus and prairie. Soil aggregation increased under perennials compared with corn, with macroaggregates dominating in switchgrass, and microaggregates in miscanthus. Isotope measurements showed that "new" C4 SOC (<5 yo) was accruing in miscanthus aggregates while switchgrass aggregates retained more "old" SOC. Miscanthus sequestered SOC at the low end of modeled estimates for the crop and switchgrass at the high end, though the rates were similar to each other (0.8-1.0 t ha-1 yr-1), and exceeded by prairie (1.3 t ha-1 yr-1). These findings indicate that perennial plants are important for belowground carbon sequestration, and that perennial crops have the benefit of management practices that reduce SOC loss to disturbance. Restored prairie, rarely considered for bioenergy due to low yields, accrues SOC at faster rates than miscanthus or switchgrass, and the conversion of marginal agricultural lands to conservation zones for grassland restoration may be a viable alternative to cropping for purposes of soil health.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.B44A..06K
- Keywords:
-
- 0402 Agricultural systems;
- BIOGEOSCIENCES;
- 0465 Microbiology: ecology;
- physiology and genomics;
- BIOGEOSCIENCES;
- 0470 Nutrients and nutrient cycling;
- BIOGEOSCIENCES;
- 0486 Soils/pedology;
- BIOGEOSCIENCES