Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/15/2000
Publication Date: N/A
Interpretive Summary: Fixation of carbon dioxide from the atmosphere into plants via photosynthesis and subsequent storage of that carbon in stable organic forms in soil has the potential to mitigate rising levels of atmospheric carbon dioxide. Managing forages with grazing cattle is a viable, low-capital economic option for land owners and could improve soil organic carbon. The effect of pasture management on soil organic carbon storage is however, not well understood. We evaluated three different fertilization strategies and four different harvest management strategies during five years of bermudagrass growth on soil organic carbon accumulation and compaction. Soil compaction was little affected by grazing pressure and fertilization strategy. Grazing at low and high pressures during the summer resulted in equivalent rates of soil organic carbon accumulation, which were more than three times that of hayed and unharvested management. Fertilization with broiler litter, a source of nutrients and organic carbon, did not affect soil organic carbon storage compared with inorganic fertilization. The impact of cattle grazing on soil organic carbon storage was positive and on soil compaction was neutral.
Technical Abstract: Forage management has the potential to influence storage of large quantities of C in soil, and therefore, help mitigate rising atmospheric CO2 levels. We evaluated the effects of N fertilization [inorganic, crimson clover (Trifolium incarnatum L.) cover crop plus inorganic, and broiler litter] and harvest strategy (unharvested, low grazing pressure, high grazing pressure, and hayed monthly) on soil bulk density, soil organic C and total S, and surface residue C and S during the first five years of 'Coastal' bermudagrass management. Soil bulk density of the 0 to 60 mm depth decreased 0.06 Mg/m3/yr due to increasing soil organic matter with time. Soil organic C did not respond significantly to fertilization strategy during the five years. Low and high grazing pressure were similar in their effect on soil organic C accumulation, averaging 1.4 Mg/ha/yr. Most of the change in soil organic C occurred in the 0 to 20 mm depth. Soil lunder unharvested and hayed management accumulated organic C at rates less than half of those observed under cattle grazing. Grazing appears to have increased the processing (i.e., initial decomposition) of forage and surface residue, which then contributed to the accumulation of soil organic C.