Frações químicas e oxidáveis da matéria orgânica do solo sob diferentes sistemas de manejo, em Latossolo Vermelho

Abstract

Resumo -O objetivo deste trabalho foi avaliar a qualidade do solo a partir das frações químicas e oxidáveis da matéria orgânica (MOS) em áreas com diferentes sistemas de manejo. O trabalho foi realizado no Município de Guaíra, no Oeste do Paraná, em áreas com diferentes tempos de adoção do sistema plantio direto (SPD, 6, 14 e 22 anos), com sucessão das culturas soja (verão) e milho/trigo (inverno), além de áreas com 12 anos de SPD -no mesmo arranjo de sucessão -mais quatro anos de cultivo de braquiária (Urochloa ruziziensis) consorciada com milho (M+B) e com pastagem e mata nativa. As frações químicas de ácido fúlvico (AF), ácido húmico (AH) e humina (HUM) foram avaliadas, bem como as frações oxidáveis da MOS (F1, F2, F3 e F4), o carbono total (CT) e o estoque de carbono (C) nas frações húmicas. Os teores de CT aumentaram com o tempo de adoção do SPD, principalmente entre SPD 6 e SPD 22 . Verificou-se predomínio da fração HUM e movimentação de AH e AF na camada de 0,0-0,4 m de profundidade. As frações oxidáveis apresentaram equilíbrio na distribuição do conteúdo de C, com maiores teores nas frações mais lábeis, em superfície. O cultivo com sucessão de culturas contribui para o aumento das frações mais lábeis, mas não para o aumento das frações mais recalcitrantes do C.Termos para indexação: Urochloa ruziziensis, carbono lábil, estoque de carbono, fracionamento da matéria orgânica, qualidade do solo, substâncias húmicas. Chemical and oxidizable fractions of soil organic matter under different management systems in an OxisolAbstract -The objective of this work was to evaluate soil quality from soil organic matter (SOM) chemical and oxidizable fractions in areas with different management systems. The study was carried out in the municipality of Guaira, in the west of the state of the Paraná, Brazil, in areas with different adoption times of the no-tillage system (NT; 6, 14, and 22 years), with succession scheme of soybean (summer) and corn/wheat (winter) crops, besides areas with 12 years under NT -in the same succession scheme -plus four years of Urochloa ruziziensis intercropped with maize (M+U), and with pasture and native forest. The chemical fractions of fulvic acid (FA), humic acid (HA), and humin (HUM) were evaluated, as well as the oxidizable fractions of MOS (F1, F2, F3, and F4), total carbon (TC), and carbon storage (C) in the humic fractions. Total carbon contents increased with the increasing adoption of time of SPD, especially from NT 6 to NT 22 . Humin fraction predominance was observed, with movement of HA and FA in the 0.0-0.4 m soil depth. The oxidizable C fractions showed equilibrium in the distribution of C contents, with higher levels in the more labile fractions, at surface. The cultivation with succession of crops contributes to the increase in labile fractions, but not to the increase of the more recalcitrant fractions of C.

Organic Matter Fractions and Carbon Management Index in Oxisol Under Integrated Agricultural Production Systems

“…The results observed in HI in the RNAN management indicate a higher degree of humification and, consequently, a higher composition of the humic substances, exceeding the range of 70 to 90% found in the literature about the participation of the contents of soil organic carbon (Primo et al, 2011;Rosset et al, 2016;Mendonç a & Matos, 2017). Probably due to the presence of forage turnip that has high nitrogen cycling capacity, and tends to enhance the decomposition of waste.…”

“…Considering the result of the HA/FA ratio in the O60 management, we observed an increase in the levels of HA compared to the FA. This shows an evolution of soil organic matter, and can be linked to the soil management or simply to the characteristics of the soil, due to better specific conditions for the increase of the fraction HA (Rosset et al, 2016).…”

“…The conversion of natural vegetation to the implantation of agricultural activities causes an imbalance in the ecosystem, since the adopted management will influence the physical, chemical and biological processes of the soil. In this way, the understanding of the performance of different soil management systems allows us to subsidize strategies for the maintenance of its long-term effects, in order to guarantee the sustainability and the quality of natural resources (Rossi et al, 2012;Rosset et al, 2016).…”

“…One of the ways of assessing soil quality is by quantifying the organic carbon content related to humic (SH) and oxidizable substances from SOM (Ebeling et al, 2011;Rosset et al, 2016), serving as indicators of the fractionated carbon content and sustainability performance management. They are considerable indicators of the processes and the degree of humification of the SOM, presenting around 70 to 90% of the total organic carbon (TOC) of the soil being divided into 3 fractions: humic acids (HA), fulvic acids (FA) and humin (HUM) (Primo et al, 2011;Rosset et al, 2016;Mendonç a & Matos, 2017). Oxidizable fractions, quantified by different degrees of oxidation of the SOM, are used as indicators of the impacts caused by the management about the content and deposition of SOM (Rangel et al, 2008).…”

“…According to Chan et al (2001), there are four fractions: F1, F2, F3 and F4. Fractions F1 and F2 are associated with the formation of macroaggregates and nutrient availability, being the F1 fraction the greater lability in the soil (Guareschi et al, 2013;Rosset et al, 2016) and the F3 and F4 fractions are related to greater chemical stability compounds, resulting from the decomposition and humification of SOM, being the F4 of greater resistance to degradation and consequent longer time permanence in soil (Rangel et al, 2008;Guareschi et al, 2013).…”