Soil carbon cycling and stabilization in a no-tilled cropping system on Oxisols under nitrogen fertilization

• Ano de defesa: 2024
• Autor(a) principal: Mota Neto, Laudelino Vieira [UNESP]
• Tipo de documento: Tese
• Tipo de acesso: Acesso aberto
• Idioma: eng
• Instituição de defesa: Universidade Estadual Paulista (Unesp)
• Palavras-chave em Português: Soil carbon saturation; Intercropping; 13C natural abundance; Random Forest; Particulate (POM) and mineral-associated (MAOM) organic matter
• Link de acesso: https://hdl.handle.net/11449/258386; http://lattes.cnpq.br/8348699269295383; https://orcid.org/0000-0001-8368-9912

Understanding carbon (C) dynamics in sustainable agricultural tropical systems is crucial for enhancing Brazil’s role in discussions on nature-based solutions for C sequestration in the tropics. In this research, we assessed whether intercropped maize-forage systems, with and without nitrogen (N) fertilization, promote C cycling in the soil. We tested the concept of C saturation and explored the controls on soil organic matter (SOM) formation, focusing on tropical croplands. In the first chapter, we evaluated whether new C inputs from maize intercropped with ruzigrass (Urochloa ruziziensis cv. Comum), palisade grass Urochloa brizantha cv. Marandu), and Guinea grass (Megathyrsus maximum cv. Tanzânia) in the presence or absence of N fertilization affect soil aggregation and C cycling. We specifically examined the bulk soil, particulate (POM) and mineral-associated organic matter (MAOM) fractions, as well as macro- and microaggregates, up to 40 cm soil depth, by measuring variations in the abundance of the natural isotope 13C. New C inputs promoted C cycling in bulk soil, POM, MAOM, and macro- and microaggregates, although these effects were restricted to the topsoil. N fertilization of the intercropped maize–forage systems reduced the proportion of aggregates >2 mm and the mean weight diameter of aggregates by lowering soil pH. Aggregates >2 mm and > 0.5 mm were significant sinks of C and N up to a soil depth of 40 cm. In the second chapter, we tested the hypothesis of C saturation in MAOM in Brazilian croplands and examined the effect of N fertilization on C stabilization in POM and MAOM fractions. We also analyzed the influence of climate, soil texture and chemical attributes on POM and MAOM formation using a Random Forest machine-learning algorithm. Our findings indicated no C saturation in MAOM and no significant effect of N fertilization on POM and MAOM levels. Our Random Forest (RF) model accurately predicted MAOM but only poorly POM. Key predictors for MAOM and POM formation included total organic carbon (TOC), total N, silt plus clay, phosphorus (P), and soil depth, zinc (Zn), cation exchange capacity, TOC covariates, respectively. The results provide insights into C cycling across SOM pools and aggregates, highlight the C saturation status in croplands and emphasize the role of N, climate, soil chemical attributes and texture in determining C distribution into MAOM and POM across soil depths in tropical conservation agricultural systems.