Land-use change and agricultural intensification: impacts on carbon and nitrogen distribution in soil profiles of the Amazon-Cerrado frontier

• Ano de defesa: 2024
• Autor(a) principal: Popin, Gustavo Vicentini
• Tipo de documento: Tese
• Tipo de acesso: Acesso aberto
• Idioma: eng
• Instituição de defesa: Biblioteca Digitais de Teses e Dissertações da USP
• Palavras-chave em Português: Agricultura tropical; Carbon sequestration; Deep soil; Deforestation; Desmatamento; Inorganic nitrogen; Matéria orgânica do solo; Nitrogênio inorgânico; Sequestro de carbono; Soil organic matter; Solos profundos; Tropical agriculture
• Link de acesso: https://www.teses.usp.br/teses/disponiveis/11/11140/tde-11032025-142410/

Land-use conversion and agricultural intensification drive widespread and rapid change of carbon (C) and nitrogen (N) on the low-relief, deep, and highly weathered soils of Amazon-Cerrado transition region of Brazil. Native vegetation removal for pasture or cropland typically leads to declines of C and N stocks in surface soils. However, less is known about the dynamic of C and N changes in deep-soil profiles. To understand the C and N dynamics in deep-soils subject to land-use change and agricultural intensification, soil samples up to 800 cm were collected beneath native forest, minimum tillage soybean, soybean-corn cropland, pasture, and a recently deforested area at Fazenda Tanguro (northeastern region of the Mato Grosso State, Brazil). In these samples, we determined soil C and N concentrations, mineral-associated organic matter (MAOM), particulate organic matter (POM), δ13C, water-extractable C (WEC) and N (WEN), ammonium (NH4+), nitrate (NO3-) and soil pH (CaCl2). The 16s rRNA and ITS amplicon sequencing was used to assess the abundance, structure, composition, and diversity of soil bacteria and fungi. Soil C stocks to 800 cm ranged from 168 Mg ha-1 to 288 Mg ha-1. Regardless the land-use, top 100 cm contained between 30% to 40% of the C stock to 800 cm, and about 50% of all soil C stocks was concentrated until 300 cm. Conversion of native forest to no-till single-cropping soybean negatively impacted soil C until 100 cm through reduction of MAOM stocks. Production intensification on the cropland led to superficial soil C accrual. Pasture showed great potential to store C through POM inputs on subsoil. The recent deforested area showed reduces in soil N stocks by 40% in the first 10 cm soil layer, but greater soil N stocks by the 100 to 300 cm soil layer compared to native forest. In cropland, N in the POM were similar to native forest, while the N linked to MAOM remained lower. Soil N stocks to 800 cm varied from 14 Mg ha-1 to 18 Mg ha-1 with no significative difference among land-uses. Overall, 40% and 60% of the total soil N stock to 800 cm were in the first 100 cm and 300 cm, respectively. Recent deforested area showed the largest soil inorganic-N (NH4+ and NO3-) stocks until 800 cm, large portion in the first 0-200 cm; cropland (both single and double crop) had the greatest inorganic-N from 200 to 600 cm. Native vegetation and double-cropped systems exhibited the highest microbial abundance, while deforested and no-till systems showed lower levels. Sequencing analysis revealed significant differences in microbial community composition, although diversity indices did not indicate substantial variation among land-uses. Furthermore, network analyses highlighted structural differences in bacterial and fungal communities influenced by land management practices. This study enhances the understanding of carbon and nitrogen dynamics in both surface and deep soils, offering valuable insights into the impacts of land-use change and agricultural intensification on soil health. Finally, based on these findings, we recommend that studies related to the impacts of agricultural expansion and intensification on the dynamics of soil C and N pools should focus efforts on sampling at least 100 cm deep in the soil, with stratified collections each 10 cm in the surface layers (up to 50 cm), and extend it to at least 300 cm, considering more areas, soil types, soil attributes, and land-uses.