Carbon and nitrogen cycling in an integrated soybean-beef cattle production system under different grazing intensities

Authors: ASSMANN, JOICE - Federal University Of Rio Grande Do Sul; ANGHINONI, IBANOR - Federal University Of Rio Grande Do Sul; MARTINS, AMANDA - Federal University Of Rio Grande Do Sul; COSTA, SERGIO E.V.G.A. - Federal University Of Rio Grande Do Sul; KUNRATH, TAISE - Federal University Of Rio Grande Do Sul; BAYER, CIMELIO - Federal University Of Rio Grande Do Sul; CARVALHO, PAULO C.F. - Federal University Of Rio Grande Do Sul; Franzluebbers, Alan

Submitted to: Pesquisa Agropecuaria Brasileira
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/24/2015
Publication Date: 10/1/2015
Citation: Assmann, J.M., Anghinoni, I., Martins, A.P., Costa, S., Kunrath, T.R., Bayer, C., Carvalho, P., Franzluebbers, A.J. 2015. Carbon and nitrogen cycling in an integrated soybean-beef cattle production system under different grazing intensities. Pesquisa Agropecuaria Brasileira. 50:967-978.

Interpretive Summary: Integrated crop-livestock systems have the potential to enhance agricultural sustainability by sharing of resources, thus reducing reliance on external inputs and/or reducing nutrient losses to the environment. Data to support these concepts require investigation under a wide range of conditions. A soil scientist at USDA-Agricultural Research Service in Raleigh NC teamed with a group of scientists from the Federal University of Rio Grande do Sul in Brazil to assess the effects of grazing intensity on carbon and nitrogen release from crop residues and animal manures in a soybean cropping system with grazed winter cover crop. Carbon and nitrogen release from soybean residues were not affected by grazing intensity. Total carbon and nitrogen were influenced by greater dry matter produced when pastures were either lightly grazed or ungrazed. These results will help farmers and scientists in Brazil and in the USA develop a better understanding of how nutrients are cycled in complex agricultural systems so that agricultural efficiency can be further improved to develop robust production systems with minimal losses to the environment.

Technical Abstract: The objective of this work was to evaluate the effect of grazing intensity on the decomposition of cover crop pasture, dung, and soybean residues, as well as the C and N release rates from these residues in a long-term integrated soybean-beef cattle system under no-tillage. The experiment was initiated in 2001, with soybean cultivated in summer and black oat + Italian ryegrass in winter. The treatments consisted of four sward heights (10, 20, 30, and 40 cm), plus an ungrazed area, as the control. In 2009–2011, residues from pasture, dung, and soybean stems and leaves were placed in nylon-mesh litter bags and allowed to decompose for up to 258 days. With increasing grazing intensity, residual dry matter of the pasture decreased and that of dung increased. Pasture and dung lignin concentrations and C release rates were lower with moderate grazing intensity. C and N release rates from soybean residues are not affected by grazing intensity. The moderate grazing intensity produces higher quality residues, both for pasture and dung. Total C and N release is influenced by the greater residual dry matter produced when pastures were either lightly grazed or ungrazed.