Methanogenesis and denitrification in soil with xaraés grass under grazing by supplemented beef cattle

• Grant number: 25/05678-2
• Support Opportunities: Scholarships in Brazil - Scientific Initiation
• Start date: July 01, 2025
• End date: June 30, 2026
• Field of knowledge: Agronomical Sciences - Agronomy - Soil Science
• Principal Investigator: Acacio Aparecido Navarrete
• Grantee: Cauê Lemos
• Host Institution: Universidade Brasil. Campus Fernandópolis. Fernandópolis , SP, Brazil
• Associated research grant: 22/15974-0 - Strategic grazing management and supplementation towards sustainable intensification at tropical pasture-based beef cattle production systems, AP.TEM

Abstract

When evaluating different dietary supplementation strategies for cattle raised on pasture, it is important to study the environmental effects of this management practice in order to contribute to the development of more sustainable agricultural systems. The objective of this project is to investigate the abundance of the methanogenic and denitrifying microbial community present in the soil with excreta from young Nellore bulls raised on Urochloa brizantha cv. Xaraés pasture during the rainy season and supplemented with a mineral mixture or different amounts of DDGS ("dried distiller's grains with solubles") and its relationship with methane (CH4) and nitrous oxide (N2O) emissions. The experiment was conducted with the participation of the candidate for the IC scholarship during an internship at the Forage Sector of FCAV-UNESP, Jaboticabal Campus, in a U. brizantha cv. Xaraés pasture established 20 years ago. In total, 60 animals were kept in an area of 21 ha, divided into 12 paddocks, during the rainy season (November 2023 to April 2024) and the animal rearing phase. Nellore young bulls were used in four treatments with three replicates: 1 - Mineral supplement (ad libitum); 2 - Protein-energy supplement (0.25% of body weight); 3 - Protein-energy supplement (0.5% of BW); and 4 - Protein-energy supplement (0.75% of BW) and control with mineral salt (0.5% body weight/day). The supplements were formulated with DDGSINPASA + Probeef MaDDGic. After 15 days of adaptation to protein-energy supplements, urine was collected from approximately 15 Nellore bulls (average of 5 animals for each treatment) weighing 240 kg initially, with weight variation over time, and the stocking rate was adjusted as necessary. To obtain soil samples for extraction of genomic DNA and quantification of the abundance of genes associated with the methanogenesis and denitrification processes, urine from the 60 animals kept on the experimental areas delimited in paddocks was added. Urine was added to the center of the chambers, simulating urination in the area covered by the base of static chambers. Gas samples were collected from six static chambers in each of the 12 paddocks, corresponding to the four experimental treatments with protein-energy supplements and control treatment, and analyses were performed by gas chromatography. DNA extraction from soil samples and determination of the copy number of the mcrA (methanogenesis) and nirk, nirS, and nosZ (denitrification) genes are part of the methodology of this project. For this purpose, the real-time quantitative PCR (qPCR) technique will be used and the results will be subjected to an analysis of variance. The means will be compared by the Scott Knott test at the 5% probability level. The determination of CH4 and N¿O fluxes from the soil were carried out within the scope of FAPESP Process 2022/15974-0, in force in the Forage Sector of FCAV-UNESP, Jaboticabal Campus. The expected goal of this project is to provide support for sustainable animal production in a tropical pastoral ecosystem and to promote research training at the Scientific Initiation level. (AU)