Frações da matéria orgânica e índice de manejo de carbono em sistemas de uso do solo.

Abstract

Anthropogenic impact on the planet is seen as one of the main causes of climate change. In light of these changes, land use patterns have become a focus, especially in relation to agriculture. Soil plays an important role in sinking greenhouse gases. Soil represents the largest carbon (C) reservoir in the terrestrial ecosystem, with an estimated storage of 2,500 Pg C. However, the replacement of natural ecosystems with agroecosystems with economically important crops often leads to a decline in the soil's organic carbon content. In this context, this work aims to quantify changes in the quantity and quality of soil organic matter and the contribution of different land use systems (sabiá, pasture, bamboo, and native forest) to greenhouse gas emissions. The study was conducted in the municipality of Areia, Paraíba, which is part of the Brejo Paraibano microregion. A completely randomized design was used with four land use systems: 1. Native Forest Area (Montane Ombrophilous Secondary Forest - N), 2. Bamboo Area (Bambusa vulgaris - B), 3. Sabiá Area (Mimosa caesalpiniifolia - S), and 4. Pasture Area (Urochloa decumbens - P), with three replicates per system at four soil depths (0-10; 10-20; 20-30 and 30-40 cm). The fertility of the samples and organic matter were analyzed at the four depths. There were consistent differences between land use systems in terms of fertility and organic matter, with pasture and bamboo areas showing higher levels of SB (P - 84.6 cmol.c; B - 80.3 cmol.c; N - 57.5 cmol.c; S - 55.4 cmol.c), CEC (P - 79.3 cmol.c; B - 78.8 cmol.c; N - 53.6 cmol.c; S - 51.6 cmol.c) and V (P - 96.1 cmol.c; N - 92 cmol.c; S - 91.4 cmol.c; B - 90.9 cmol.c). For organic matter analysis, bamboo and native forest showed the highest levels of SOM (B - 24.5 mg.g-1

; N - 22.9 mg.g-1

; S - 15.3 mg.g-1

; P - 13.7 mg.g -1 ), MOP

( B – 2.53 mg.g-1

; N – 1.43 mg.g-1

; S – 0.88 mg.g-1

; P – 0.77 mg.g-1

), COM ( B- 11.84 mg.g-1 ;

N - 11.83 mg.g-1

; S – 8.05 mg.g-1

; P – 7.23 mg.g-1

) and TOC (B- 14.38 mg.g-1

; N – 13.27 mg.g- 1

; S – 8.79 mg.g-1

; P – 8.00 mg.g-1

). Carbon storage (CS) was higher in the first 20 cm of soil, but in bamboo and native forest areas this storage remained constant with approximate values (B – 24.8 Mg.ha-1

; N – 24.0 Mg.ha-1

) compared to the sabiá and pasture area (S – 15.2 Mg.ha- 1; P – 8.00 Mg.ha-1). The carbon management index proved to be highly sensitive to land use

type, with the Sabiá area showing the highest value (377), higher levels of Fulvic Acid (B - 4.93 mg.g-1

; N - 3.68 mg.g-1

; S - 3.14 mg.g-1

; P - 1.96 mg.g-1

), Humic Acid (B - 101.8 mg.g-1 ;

N - 86.1 mg.g-1

; S - 83.2 mg.g-1

; P - 80.0 mg.g-1

) and Humin (B - 45.8 mg.g-1

; N - 34.0 mg.g-1 ;

S - 22.5 mg.g-1

; P - 17.3 mg.g-1

). The highest levels of Humic Substances were observed in the bamboo and native forest system, where the cycling and nutritional dynamics promoted by Microbiota opens up opportunities for research and investigation. The results demonstrate a greater capacity for carbon complexation, greater stability in the systems, and a higher degree of humification. Therefore, it is concluded that forest and agroforestry systems promote greater accumulation, stabilization of soil carbon, contributing to a better interaction between residue input and soil organic matter (SOM). Keywords: forest systems; soil organic matter; carbon stock; semi-arid region.