Submitted to: Agriculture, Ecosystems and Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/7/2013
Publication Date: 12/1/2013
Citation: Fultz, L.M., Moore-Kucera, J., Zobeck, T.M., Acosta Martinez, V., Allen, V. 2013. Organic carbon dynamics and soil stability in five semiarid agroecosystems. Agriculture, Ecosystems and Environment. 181(1):231-240. 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 five agroecosystems on different types of SOC and compared the ICLs to conventional cotton, a major crop in the Shouthern High Plains. Baseline surface (0-2 inches) and subsurfaces (2-6 inches) 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 also more stable in water compared to the soils managed in conventional cotton. The soils managed as ICL also had more SOC more aggregates that did not distrupt as easily in rainfall than the conventionally tilled cotton soil. This study also showed that, overall, perennial grasses resulted in the greatest potential for better soil aggregation and carbon storage when compared to the continuous crop production.
Technical Abstract: In the semiarid Texas High Plains where continuous cotton (CTN) is the dominate cropping practice, alternative agroecosystems such as integrated crop-livestock agroecosystems (ICL) are gaining interest for their versatility in management approaches to conserve water in this water-limited environment. However, the benefits on soil ecosystem services related to carbon sequestration are still evolving. Five agroecosystems were selected to examine the effects of management practices on mean weight diameter, aggregate distribution, and soil organic C. Agroecosystems included three ICL’s with a variety of management practices combined with stocker steer grazing and two subsurface drip irrigated (SDI) CTN agroecosystems. The first ICL agroecosystem (FRG_CTN) included paddocks of perennial native grasses, millet and cotton (planted in rotation), and SDI (buffer) old world bluestem. The second ICL agroecosystem (OWB_BER), a SDI (deficit) agroecosystem, included paddocks of bermudagrass and old world bluestem, while the third ICL agroecosystem (FRG_RC) included paddocks of center-pivot irrigated old world bluestem and row crop production. Soil samples (0-5 and 5-20cm) were collected in July 2010, and fractionated into water stable macroaggregate (>250 µm), microaggregate (53-250 µm), silt+clay (<53 µm) fractions. The macroaggregates were further fractionated into intra-aggregate particulate organic matter (>250 µm), microaggregate (53-250 µm), and silt+clay (<53 µm) fractions. Alternative ICL practices resulted in greater mean weight diameter, soil organic C SOC content, and macroaggregate proportions, with the FRG_RC agroecosystem providing the greatest improvements compared to continuous cotton production. Overall, perennial grasses resulted in the greatest potential for aggregate stability and C sequestration when compared to the continuous crop production.