Intensification and integration of pastures: a soil chemical and biological study in a tropical area

Author(s)

João Vitor dos Santos

• Document type: Master's Dissertation
• Press: São Carlos.
• Institution: Universidade de São Paulo (USP). Instituto de Química de São Carlos (IQSC/BT)
• Defense date: 2022-08-16

Examining board members

Ladislau Martin Neto; Alberto Carlos de Campos Bernardi; Wilson Tadeu Lopes da Silva

• Advisor: Ladislau Martin Neto

Abstract

Brazil is the largest exporter and the second-largest beef producer in the world. The country\'s biggest challenge has been to increase the productive capacity of soils in an environmentally sustainable way. In this context, agricultural practices that preserve the environment have demonstrated high productivity and sustainability, emphasizing intensive grazing management and integrated production systems, such as crop-livestock-forest integration (ICLF), and its crop-livestock (ICL) and livestock-forest (ILF) variations. Well managed pastures, with adjustment of the animal stocking rate, lime application, fertilizers and adoption of technological processes can influence the quantity and quality of soil organic matter, as well as soil biological activity. In this study, the effects of the conversion of a native forest (FO) into different pasture-based beef cattle production systems were assessed in long-term field experiments using soil chemical, physical and biological attributes. Five pasture systems were evaluated: i) irrigated high stocking rate pasture (IHS); ii) rainfed high stocking rate pasture (RHS); iii) rainfed medium stocking rate pasture (RMS); iv) livestock-forest integration with moderate stocking rate, with two variations, samples collected between the rows of trees (ILF- BR) and in the tree rows (ILF-R), and v) degraded pasture (DP), the latter used as a reference for conventional pasture management, extensively used by farmers. Soil samples were collected in two ways, i) in subdivision of six layers, up to one meter deep, for chemical analysis of dissolved organic matter (DOM), and ii) only in the superficial layer (0-10 cm) for analysis of some chemical, physical, and biological indicators of whole soil samples. The results of the first part (i) showed that the concentration of dissolved organic carbon (DOC) decreased with depth in the soil profile. The most aromatic DOM and with the highest molecular weight (higher SUVA254 and lower SR indices) persisted on the surface and both parameters decreased until the last soil layer (60-100cm). The combination of fluorescence (FI), humification (HIX) and biological (BIX) indices suggested that the DOM in the surface layers has a great contribution from terrestrial sources (plants) and along the profile greater microbial contributions, possibly due to its leaching to deeper layers. Among the relevant results, the RMS system presented DOM with greater lability and susceptible to microbial attack and the DP more aromatic and persistent. The results obtained by Fourier Transform Ion Cyclotronic Resonance Mass Spectrometry (FT-ICR MS) showed the complex nature of DOM, with thousands of peaks, each representing a unique chemical formula. Lignin persistence was observed at soil depths when compared to the other biochemical classes evaluated. However, new molecules were also formed with depth, with an increase in by-products that indicate to be of microbial origin, such as fatty acids. The results of the second part (ii) showed that all managed pastures showed an increase in soil carbon content in relation to DP (16.2±1.7 g kg-1), with emphasis on the RMS that presented the highest content (32.9±0.9 g kg-1). The activities of -glucosidase (BGL) and arylsulfatase (ARYL) enzymes showed greater sensitivity to detect management changes than microbial biomass carbon (MBC) and soil basal respiration (BR). Higher activities of BGL and ARYL enzymes were observed in the RMS system, possibly due to the combination of the higher input of biomass, and the quality of DOM, the most bioavailable fraction for the microbiota, which showed a predominant aliphatic character compared to the other managements. The results obtained in this study showed that the conversion of low-productivity pastures into well-managed and integrated systems can lead to improvements in soil chemical and biological attributes. (AU)

• FAPESP's process: 20/04938-7 - Quantification and spectroscopic characterization of dissolved organic matter in soils under pastures and integrated production systems
• Grantee: João Vitor dos Santos
• Support Opportunities: Scholarships in Brazil - Master