Substâncias Húmicas Em Cambissolo Sob Vegetação Natural E Plantios De Pinus Em Diferentes Idades

Abstract

RESUMODevido à grande área ocupada com reflorestamentos de pinus no sul do Brasil, considera-se necessário avaliar o impacto dessa cultura no estoque de carbono orgânico do solo, especialmente com relação às frações das substâncias húmicas (SH). Nesse contexto, o presente trabalho teve como objetivo avaliar as alterações na quantidade e proporção das substâncias húmicas da matéria orgânica em solo representativo do Planalto Catarinense devido à substituição da vegetação natural por povoamentos de Pinus taeda. Foram avaliadas quatro situações de uso em áreas localizadas no município de Ponte Alta, sendo uma de campo natural (CN) e três plantios de Pinus taeda com idades de 5 (P05), 16 (P16) e 21 (P21) anos em segunda rotação, em solo classificado como Cambissolo Húmico distrófico. Amostras de solos compostas por sete sub amostras foram coletadas em sete pontos amostrais dentro de cada área nas camadas de 0-5 cm, 5-10 cm, 10-20 cm, 20-30 cm e 30-40 cm de profundidade. Os teores de carbono das SH da matéria orgânica do solo (MOS) foram determinados através de fracionamento químico resultante da solubilização em meios ácido e básico. Os teores e proporções das SH da MOS variaram significativamente em função da situação de uso e profundidade analisados, evidenciando maiores quantidades na camada superficial e seu aumento com a idade do pinus. Em geral, os maiores valores de C nas frações e camadas avaliadas foram observados no P21 e os menores no P05. Palavras-chave: fracionamento; ácidos húmicos; reflorestamento; sequestro de carbono. ABSTRACTDue to the great area occupied with Pinus sp. plantations in southern Brazil, it is considered necessary to evaluate the impact of this kind of crop on soil organic carbon stock, specially related to fractions from humic substances (HS). On this context, this work aims to evaluate the changes on humic substances quantity and the proportion of organic matter on representative soil of the highlands in Santa Catarina state due to replacement of natural grassland by Pinus taeda stands. Four situations of soil use on areas located in Ponte Alta town were evaluated, being one of natural grasslands(CN) and tree of Pinus taeda forests with 5 (P05), 16 (P16) and 21 (P21) years old on second rotation, on soil classified as Humic Dystrupept. Soil samples composed by seven subsamples were collected on seven points inside every area in the 0-5 cm, 5-10 cm, 10-20 cm, 20-30 cm, 30-40 cm layers. The carbon contents of HS in the SOM were determined by chemical fractionating resulted from alkaline or acid extraction. The HS contents and proportions varied according to the soil use and depth analyzed, showing more quantity in the surface layer and its increasing with pinus age. In general, the highest levels of C on fractions and layers evaluated were observed on P21 and the lowest on P05 uses.

Changing the land use from degraded pasture into integrated farming systems enhance soil carbon stocks in the Cerrado biome

“…SOM chemical fractionation showed that most of the TOC was protected in the more stable and recalcitrant fraction (C-HUM), regardless of the system and soil depth (Table 2), corroborating other studies (Freitas et al, 2020;Almeida et al, 2021;Frazão et al, 2021). The C-HUM fraction comprises compounds of higher molecular weight, lower number of carboxylic groups, and higher number of nitrogenous groups, providing higher stability and remaining time in the soil (Pfleger, Cassol, & Mafra, 2017), allowing most TOC to be stored in this fraction. Coser et al (2018) also related this storage to the formation of humus-clay colloidal complexes.…”

Genetic improvement of Ilex paraguariensis in western Santa Catarina State: estimate of phenotypic and genetic parameters

“…These results can be explained by differences in the soil qualities in the experiments, as these soils present integrated physical, chemical and biological properties (Srivastava et al, 2019). When converting natural areas into pine forests, these properties are modified, increasing the content and stabilization of organic carbon in the soil that is strongly influenced by rotation (Pfleger et al, 2017). This seems to be the most plausible explanation for the different averages for the experiments herein, since the Guatambu area was previously occupied by a Pinus sp.…”

Carbon and chemical fractionation of soil organic matter in irrigated banana plantation subjected to conservation practice

“…The HA/FA ratio is used as an indicator of the humification process and represents the level of evolution of SOM (Pfleger et al, 2017). Ratios greater than 1.0 are indicative of greater transformation in SOM.…”