Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/27/2013
Publication Date: 9/20/2013
Citation: Fultz, L.M., Moore-Kucera, J., Zobeck, T.M., Acosta Martinez, V., Allen, V. 2013. Aggregate carbon pools after 13 years of integrated crop-livestock management in semiarid soils. Soil Science Society of America Journal. 77(5):1659-1666. Interpretive Summary: Semi-arid regions have the potential to store soil organic carbon (SOC) but the rate of storage depends on the management of the soil. Systems that include livestock as well as pasture with row crops (called integrated crop livestock systems, ICL) may be able to store more SOC and protect the soil clods (aggregates) from erosion. This study evaluated the effects of long-term ICL systems on different types of SOC and compared the ICLS to conventional cotton, a major crop in the Shouthern High Plains. Baseline surface (0-6 inches) were collected in 1997 and then again in 2010. The samples were sieved into different size classes and tested to determine how much SOC was stored and how they broke down in water. The combination of reduced tillage and increased vegetation in the pastures produced a larger amount of larger aggregates that were alsomore stable in water compared to the soils managed in conventional cotton. The soils managed as ICL also had 22% more SOC than the conventionally tilled cotton soil. This study also showed that, overall, the ICL had more potential to store SOC than the conventionally tilled cotton soil.
Technical Abstract: Semi-arid regions have the potential to sequester soil organic carbon (SOC) but the magnitude and rate of sequestration is highly management specific. Integrated crop-livestock (ICL) systems that utilize perennial or high-residue no-till annual forage crops as part of the overall agronomic system may sequester more SOC and protect soil aggregates from erosion. This study examined the long-term effects of ICL management on SOC pools in comparison to continuous cotton (CTN) management at both the system and the individual paddock scale. Baseline soil samples (0-15 cm) collected in 1997 and those collected in 2010 were fractionated into six distinct organo-mineral complexes including: water stable macroaggregate (>250-µm), microaggregate (53-250-µm), silt+clay (<53-µm), and intra-aggregate particulate organic matter (>250-µm), microaggregates (53-250-µm), and silt+clay (<53-µm) fractions. The combination of reduced tillage disturbance and increased vegetative inputs under grassland management of the old world bluestem component in the ICL resulted in increased proportions of the macroaggregates (59%) compared to the CTN system as well as enhanced aggregate stability as measured by mean weight diameter (1.5 mm in old world bluestem compared to 0.40 mm in continuous cotton). The ICL system also had 22% more SOC (11.2 mg g-1) than that under CTN (9.0 mg g-1). In 2010, differences were also detected between the CTN and ICL in the macroaggregate (1.0 and 4.2 mg g-1 soil, respectively), intra-aggregate particulate organic matter (2.5 and 5.3 mg g-1 macroaggregate, respectively), and intra-aggregate microaggregate (5.4 and 8.2 mg g-1 macroaggregate, respectively) fractions. This study revealed significantly greater quantities of physically protected intra-aggregate microaggregate-SOC, increasing the C sequestration potential within the ICL systems evaluated for these semi-arid soils.