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Title: Phosphorus and potassium cycling in a long-term no-till integrated soybean-beef cattle production system under different grazing intensities in subtropics

Author
item ASSMANN, JOICE - Federal University Of Rio Grande Do Sul
item ANGHINONI, IBANOR - Federal University Of Rio Grande Do Sul
item VALADAO GIGANTE, SERGIO - Federal University Of Rio Grande Do Sul
item MARTINS, AMANDA - Federal University Of Rio Grande Do Sul
item NICHEL, GABRIELA - Federal University Of Rio Grande Do Sul
item SILVA, RODRIGO ANDRE - Federal University Of Rio Grande Do Sul
item BALERINI, FABRICIO - Federal University Of Rio Grande Do Sul
item CARVALHO, PAULO - Federal University Of Rio Grande Do Sul
item Franzluebbers, Alan

Submitted to: Nutrient Cycling in Agroecosystems
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/22/2016
Publication Date: 5/1/2017
Citation: Assmann, J.M., Anghinoni, I., Valadao Gigante, S.E., Martins, A.P., Nichel, G., Silva, R.P., Balerini, F., Carvalho, P., Franzluebbers, A.J. 2017. Phosphorus and potassium cycling in a long-term no-till integrated soybean-beef cattle production system under different grazing intensities in subtropics. Nutrient Cycling in Agroecosystems. 108:21-33.

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 phosphorus and potassium release from crop residues and animal manures in a soybean cropping system with grazed winter cover crop. Phosphorus and potassium were effectively cycled, but differences between nutrient types and sources of nutrients from cover crop residues, soybean leaves and stems, and dung were apparent. Greatest release of phosphorus and potassium were derived from cover crop and dung residues when either grazed with low intensity or not grazed at all. 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: Long-term crop-livestock integration enables constant and high nutrient cycling because animal, pasture and crop residues release nutrients at different rates. Therefore, appropriate management of these systems is needed to maximize the benefits of nutrient cycling. The objective of this study was to evaluate how grazing intensity affected the release rates of phosphorus (P) and potassium (K) in pasture, dung and soybean residues in a no-till long-term crop-livestock system. The experiment was established in 2001 on a clayey Oxisol after soybean harvest. Treatments consisted of pasture (black oat + Italian ryegrass) with sward heights maintained at 10, 20, 30 and 40 cm by different cattle stocking rates and a non-grazed (NG) reference area. Decomposition and release rates of P and K in the pasture and dung were determined using litter bags that were installed at soybean seeding and in soybean residue at pasture seeding during two pasture-crop cycles (2009 to 2011). Moderate grazing intensities resulted in greater P release rate from pasture and dung residues. Pasture and dung residues released K at a very high rate and were not influenced by grazing intensity. The P and K released from soybean residue were not affected by grazing intensity; however, decomposition of soybean leaves was greater than of stems. Greatest rates of total P and K released were from pasture and dung residues under low grazing intensity and in the non-grazed areas.