Chemical and structural characterization of soil humic substances under agroforestry and conventional systems

Abstract

SUMMARYin the 0-6 cm layer, the percentage of mass loss was highest (300-600 °C) for humic acids in the thermally most stable region. Despite the similarity between infrared spectra, soil fulvic acids in the SILV treatment extracted from 6-12 cm depth decrease the absorption bands at 1708 and 1408 cm -1 followed by an increase in the absorption band at 1608 cm -1 attributed to aromatic C=C groups. This behavior suggests an increase in the aromatic character of the structure. The AGP and ICF treatments, which increase the soil tilling, favored the maintenance of humic substances with a more aromatic character in the soil than SILV and NF. The less aromatic humic substances in the SILV treatment resulted in an increase of exchange sites of soil organic matter, indicating improved nutrient cycling and maintenance of productivity in the system. Index terms: semi-arid, silvopasture, agrosilvopasture, spectroscopy. semi-árido, silvopastoril, agrossilvopastoril, espectroscopia. RESUMO: CARACTERIZAÇÃO QUÍMICO-ESTRUTURAL DE SUBSTÂNCIAS HÚMICAS DO SOLO SOB SISTEMAS AGROFLORESTAIS E CONVENCIONAL Estudos comprovam que na região semiárida cearense sistemas agroflorestais aumentam os teores de C orgânico do solo. Entretanto, não há registro se tal incremento implica também mudanças qualitativas nos diferentes compartimentos da matéria orgânica do solo. O objetivo deste estudo foi verificar possíveis alterações das características químico-estruturais das frações ácidos fúlvicos e ácidos húmicos de um Luvissolo em áreas sob sistemas agroflorestais, cultivo intensivo e vegetação nativa em experimento de longa duração, instalado na região semiárida cearense. O estudo foi conduzido no campo experimental do Centro Nacional de Pesquisa de Caprinos da EMBRAPA, município de Sobral-CE, onde foram avaliados os seguintes tratamentos: agrossilvopastoril (AGP), silvopastoril (SILV), cultivo tradicional intensivo em pousio (CIP) e áreas sob mata nativa (MN). As frações ácidos fúlvicos (AF) e ácidos húmicos (AH) foram extraídas das camadas de 0-

Humification degree and its relationship with some soil physical characteristics on robusta coffee (Coffea canephora) plantation

“…This showed that the subsurface layer of soil was having a higher degree of humification than the soil surface. The HR value in this study was lower than the value of HR from Moraes et al (2011), which the HR in some agroforestry were ranging from 17% to 69%. The low value of HR affected by the low level of humification on a coffee plantation.…”

Short Communication: Soil carbon pools in different pasture systems

“…The presence of lignin derived from plant residues increased also the humin in soil (Carvalho et al, 2014). This increase in humin in soil is resulting from the loss of oxidative C and, at the same time, an increase in the C stable (Moraes et al, 2011). Therefore, the permanent inputs of organic C from herbaceous plants and Means followed by the same letter in each row and season do not differ statistically from each other at p < 0.05 (LSD test).…”

“…All plots showed a 2012). The high carbon content from FAF in this system may have stimulated microbial diversity because that fraction is more easily used as an energy source by soil microorganisms, generating more negative charges and improving nutrient cycling and ecosystem productivity (Moraes et al, 2011).…”

Soil organic matter pools in a tropical savanna under agroforestry system in Northeastern Brazil

“…Once the aggregates are broken down by cultivation, such as SBA system, the HS are exposed to microbial attack and degraded, decreasing their contents (BONGIOVANNI; LOBARTINI, 2006). Highest C-HAF contents compared to the C-FAF can be related to the synthesis process through formation of more complex structures from a structural rearrangement of less condensed molecules, such as fulvic acid fraction or the degradation process of the FAF, which is more easily used as energy source by soil microorganisms (STEVENSON, 1994;MORAES et al, 2011). However, C-HF was the most abundant fraction in all systems, which can be explained by the fact that the organic material deposited in the soil is less degraded, due to its high chemical recalcitrant (STEVENSON, 1994;FONTANA et al, 2005).…”

“…Additionally, it can be efficient marker of soil history (it suffers influences of soil formation factors like time, origin material, climate, relief and anthropomorphic action) assuming a key role (especially humic acids) as indicators of SOM quality, since during the humification process (organic residues stabilization), the humified fraction is the one that undergoes the largest structural change (CANELLAS et al, 2004;MARTINS et al, 2009;PESSOA et al, 2012). Therefore, changes in ûeld management practices, such as AFS, can alter the chemical properties of soil humic substances (MORAES et al, 2011;GUIMARAES et al, 2013) Several studies have been published in Brazil linking soil properties and AFS although most of them are concentrated in the Amazon region and featured to the soil chemical and physical attributes (SCHROTH et al, 2002;BARROS et al, 2004;BARRETO et al, 2006;PEREIRA et al, 2008;PINHO et al, 2012) with few focusing SOM pools dynamic MORAES et al, 2011;ZAIA et al, 2012). Therefore, our objective was to evaluate the influence of AFS, established in long-term, on SOM pools in a tropical soil from Northeast Brazil.…”