Long-term management impacts on soil carbon and nitrogen dynamics of grazed bermudagrass pastures

• Published in: Soil biology & biochemistry 2004-11, Vol.36 (11), p.1809-1816
• Main Authors: Wright, Alan L., Hons, Frank M., Rouquette, Francis M.
• Format: Article
• Language: English
• Subjects: Agronomy. Soil science and plant productions; Biochemistry and biology; Biological and medical sciences; carbon; Carbon mineralization; Carbon sequestration; cattle; Chemical, physicochemical, biochemical and biological properties; Cynodon dactylon; Fundamental and applied biological sciences. Psychology; grazing intensity; Lolium multiflorum; mineral fertilizers; mineralization; nitrogen; Nitrogen mineralization; Nitrogen sequestration; Organic matter; pasture management; Physics, chemistry, biochemistry and biology of agricultural and forest soils; sandy loam soils; soil nutrient dynamics; Soil organic C; soil organic matter; Soil organic N; Soil science; sowing; Trifolium
• ISSN: 0038-0717; 1879-3428
• DOI: 10.1016/j.soilbio.2004.05.004

Managed pastures have potential for C and N sequestration in addition to providing forage for livestock. Our objectives were to investigate changes in soil organic C (SOC) and soil organic N (SON) concentrations and mineralizable C and N in cattle (Bos indicus) grazed bermudagrass [Cynodon dactylon (L.) Pers.] pastures up to 32 y after establishment. Management included low- and high-grazing intensity, fertilization, and winter overseeding with annual ryegrass (Lolium multiflorum Lam.) and clover (Trifolium sp.). Soil (0–15cm) was sampled 7, 15, 26, and 32 y after establishment of Coastal and common bermudagrass pastures. No significant differences in SOC or SON concentrations were observed between Coastal and common bermudagrass pastures. Grazing strategies played important roles in C and N sequestration, as high-grazing intensity resulted in a lower increase in SOC and SON concentrations over time compared to low-grazing intensity. Increases in SOC were observed up to 26 y, while increases in SON were observed up to 32 y after establishment of bermudagrass pastures. Soil organic C increased 67 and 39% from 7 to 26 y at low-grazing intensity for bermudagrass+ryegrass and bermudagrass+clover pastures, respectively. SOC and SON concentrations did not increase beyond 15 y after bermudagrass establishment at high-grazing intensity. An exception was the Coastal bermudagrass+ryegrass pastures, which exhibited higher SON at 32 y than at 7 y at both grazing intensities. By 32 y, SON increased 83 and 45% in Coastal bermudagrass+ryegrass pastures at low- and high-grazing intensity, respectively, compared to 7 y. The introduction of clover to pastures decreased SOC and SON relative to ryegrass at high- but not at low-grazing intensity. Potentially mineralizable C increased from 7 to 15 y, while mineralizable N increased from 7 to 32 y. Potentially mineralizable N was also greater for bermudagrass+clover than bermudagrass+ryegrass pastures. Long-term increases in SOC and SON concentrations suggest that managed and grazed pastures have strong potential for C and N sequestration.