Carbon Sequestration under Irrigated Switchgrass (Panicum virgatumL.) Production

Abstract

Perennial herbaceous crops such as switchgrass are important sources of cellulosic biomass for the developing bioenergy industry. Assessments of how much C will be lost or sequestered into soil and the turnover rates of that C are needed to assist producers and policymakers in determining the long‐term sustainability of biomass production. We used the natural 13C abundance of soils to calculate the quantity and turnover of C4−C inputs in irrigated fields cropped to switchgrass monocultures. Soil profile root biomass produced after three seasons averaged 3.9 Mg C ha−1 m−1 Five years of cropping showed a 1200 kg ha−1 increase in soil organic C (SOC) in the 0‐ to 15‐cm depth increment, with no change below 15 cm. The surface 15 cm of soil cropped to ‘Kanlow’ and ‘Shawnee’ had a δ13C enrichment of 3‰ above the native uncultivated soil, with 3.6‰ for ‘Cave in Rock,’ with an average 2‰ enrichment compared with the soil collected before switchgrass establishment. Enrichment in the 30‐ to 60‐ and 60‐ to 90‐cm depths averaged 1.7 and 0.9‰, respectively. The amount of soil profile C4–C determined by δ13C analysis showed a greater C input than determined by the difference in total C mass between the uncultivated native and cropped soils. The average accrual rate of C4–SOC was estimated at 1.0 Mg ha−1 yr−1 Estimates of the mean residence time of the C3−C under the irrigated C4 monocultures of switchgrass were >60 yr in the 0‐ to15‐cm and 30 to 55 yr in the 15‐ to 30‐cm depth increments. On average, 24% of SOC in the 0‐ to 15‐cm depth was derived from C4 cropping.

Intercropping with Switchgrass Improves Net Greenhouse Gas Balance in Hybrid Poplar Plantations on a Sand Soil

“…Cumulative three-year yields ranged from 34 to 47 Mg DM ha -1 (15-20 Mg C ha -1 ) depending on the cultivar. Collins et al (2010) reported biomass yields of the switchgrass cultivar Kanlow was 3.3 Mg DM ha -1 in the establishment year and 47 Mg DM ha -1 (20 Mg C ha -1 ) over the three year study which exhibited a similar production track as found in the current study. They also reported profile root biomass of Kanlow produced after three seasons represented 3.3 Mg C ha -1 to 1-m depth and that soil C increased 20% in the 0-to 15-cm soil layer.…”

“…The IC and SM produced significantly more biomass than the PM. Collins et al (2010) and Kimura et al (2015) reported similar cumulative dry matter and C yields of irrigated switchgrass monocultures over 3 yr on a site located close to the current study on a Quincy soil. Cumulative three-year yields ranged from 34 to 47 Mg DM ha -1 (15-20 Mg C ha -1 ) depending on the cultivar.…”

“…A significant portion of the heterotrophic soil respiration was influenced by the location in the soil profile and by the total organic C content of soils. If the assumption is made that SR is 50% of R eco and that switchgrass root production was similar to that Collins et al (2010) reported for switchgrass the estimate of C accumulation would be lower but still positive for the intercropped and switchgrass treatments after 4 yr of production.…”

“…significant amount of organic matter to the soil (Ma et al, 2000a(Ma et al, , 2000bLiebig et al, 2005Liebig et al, , 2008Collins et al, 2010).…”

Influence of Composted Dairy Manure and Perennial Forage on Soil Carbon and Nitrogen Fractions during Transition into Organic Management

“…The degree of CDM decomposition and the low C and N content of the CDM added in 2009 compared with 2008 could have contributed to the increase in the C r , C s , and N r fractions in the surface 0-5 cm compared with 5-10 cm depth. In addition, irrigation in combination with adequate summer temperatures for microbial decomposition could have also contributed to the increase in the C r , C s , and N r fractions as the mineralization rate of C and N accelerated [48,49] before our field sampling in 2008 and 2009. The no-tillage management practices could also have contributed to the increase in soil C and N fractions in the surface 0-5 cm compared to the 5-10 cm depth due to the exposure of the CDM to irrigation water and ambient summer temperatures.…”