Unraveling the soil microbiome in Brachiaria pastures: exploring varietal influences and nitrogen fertilizers

Author(s)

Luis Fernando Merloti

• Document type: Doctoral Thesis
• Press: Piracicaba.
• Institution: Universidade de São Paulo (USP). Escola Superior de Agricultura Luiz de Queiroz (ESALA/BC)
• Defense date: 2024-05-29

Examining board members

Tsai Siu Mui; Letusa Momesso Marques; Acacio Aparecido Navarrete

• Advisor: Tsai Siu Mui

Abstract

Degradation of pasturelands is a critical issue confronting Brazil, a country with a prominent role in global beef production. Such degradation, resulting from practices such as overgrazing and inefficient soil management, leads to reduced land productivity and adverse environmental impacts, including soil degradation, deforestation, and increased carbon emissions. Efficient management strategies are essential to address these challenges, enhancing pasture resilience and productivity while minimizing ecological footprints. This thesis assessed the effect of Brachiaria varieties and different N fertilizers on the soil microbiome and physicochemical characteristics, followed by their effects on plant development and potential environmental consequences. Chapter 1 examined the effects of four Brachiaria varieties on soil microbial communities and nutrient cycling, utilizing a combination of molecular techniques and traditional soil analyses. The study revealed that Brachiaria varieties significantly enhance soil quality by improving porosity, organic carbon content, and phosphorus availability, while also influencing the soil\'s prokaryotic and fungal communities, especially those involved in the N cycle. Notably, the Brachiaria varieties were found to selectively enhance microbial communities beneficial for increase the availability of soil nutrients, pathogen resistance, and stress resilience, with the Ipyporã variety showing a distinct potential for improving soil quality and supporting intercropping systems. Chapter 2 explored into the rehabilitation of degraded Brazilian pastures through N fertilization, highlighting its potential to modify the soil microbiome and improve plant growth. Through the application of different N sources, including ammonium sulfate, urea, and castor meal, the study assessed their impact on the soil microbiome, nitrification processes, and Brachiaria plant growth. Findings indicated that while all N sources increase soil N availability and alter soil chemistry, ammonium sulfate is particularly effective in promoting prokaryotic over fungal growth, thus maintaining N related functions. Conversely, urea and castor meal appear to favor fungal communities associated with plant diseases, suggesting that the choice of N fertilizer profoundly affects soil microbial balance, nitrification efficiency, and plant root development. Overall, this thesis underscores the complex interplay between genetic selection of forage varieties, fertilization practices, and soil microbial communities in tropical pasture ecosystems. It highlights the importance of selecting appropriate Brachiaria varieties and N fertilizers to enhance soil health, support sustainable livestock production, and mitigate the environmental impacts of pasture degradation. (AU)

• FAPESP's process: 19/19145-5 - Ammonium-oxidizers dynamic in Atlantic Forest soils: impact of forest-to-pasture conversion and nitrogen fertilization
• Grantee: Luis Fernando Merloti
• Support Opportunities: Scholarships in Brazil - Doctorate