Organic Carbon Effects on Soil Physical and Hydraulic Properties in a Semi-arid Climate

Authors: Benjamin, Joseph; Mikha, Maysoon; Vigil, Merle

Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/8/2008
Publication Date: 9/1/2008
Citation: Benjamin, J.G., Mikha, M.M., Vigil, M.F. 2008. Organic Carbon Effects on Soil Physical and Hydraulic Properties in a Semi-arid Climate. Soil Science Society of America Journal. 72:1357-1362. doi:10.2136/sssaj2007.0389.

Interpretive Summary: Increasing cropping intensity in the central Great Plains of the United States has led to increased organic carbon being stored in the soil. A study was conducted to investigate changes in soil physical properties associated with increased OC levels. A cropping systems study was started in 1990 at the Central Great Plains Research Station near Akron, Colorado. In 2005 soil samples were taken in increments to a soil depth of 15 inches to measure OC, water stable macroaggregates, bulk density, pore size distribution and saturated hydraulic conductivity. Samples were collected from permanent grass plots, plots in a wheat-corn-millet rotation, and plots in a wheat-fallow rotation. Increasing cropping intensity significantly increased organic carbon, water stable macro-aggregates, and saturated hydraulic conductivity. Changing cropping intensity had no significant effect on bulk density or pore size distribution. Permanent grass increased organic carbon compared with the annually cropped rotations, particularly deeper in the soil. Plots in permanent grass had greater saturated hydraulic conductivity and this may indicate greater pore continuity and stability under saturated conditions. There was a poor correlation between organic carbon and other soil physical parameters. Water stable macroaggregates was better correlated with physical properties such as bulk density and saturated hydraulic conductivity in that as aggregation increased saturated hydraulic conductivity increased and bulk density decreased. Increasing soil organic carbon may not immediately lead to changes in other soil physical and hydraulic properties in a semi-arid climate. Increased biological activity may be needed to convert the crop residues into organic compounds that stabilize aggregates and soil pore systems.

Technical Abstract: Increasing cropping intensity in the central Great Plains of the United States has led to increased organic carbon being stored in the soil. A study was conducted to investigate changes in soil physical properties associated with increased organic carbon levels. A cropping systems study was started in 1990 at the Central Great Plains Research Station near Akron, Colorado. In 2005 soil samples were taken in increments to a soil depth of 370 mm to measure organic carbon, water stable macroaggregates (water stable aggregates > 250 µm), bulk density, total porosity (ptotal), water storage porosity (pws), and saturated hydraulic conductivity (ksat). Samples were collected from permanent grass plots, plots in a wheat-corn-millet rotation, and plots in a wheat-fallow rotation. Increasing cropping intensity significantly increased organic carbon, water stable macro-aggregates, and ksat. Changing cropping intensity had no significant effect on bulk density, ptotal, or pws. Permanent grass increased organic carbon compared with the annually cropped rotations, particularly deeper in the soil. Plots in permanent grass had greater ksat and this may indicate greater pore continuity and stability under saturated conditions. There was a poor correlation between organic carbon and other soil physical parameters. Water stable macroaggregates was better correlated with physical properties such as bulk density and ksat in that as aggregation increased ksat increased and bulk density decreased. Increasing soil organic carbon may not immediately lead to changes in other soil physical and hydraulic properties in a semi-arid climate. Increased biological activity may be needed to convert the crop residues into organic compounds that stabilize aggregates and soil pore systems.