Elsevier

Geoderma Regional

Volume 25, June 2021, e00392
Geoderma Regional

Carbon and nitrogen stocks and microbiological attributes of soil under eucalyptus cultivation in the Pampa biome of southern Brazil

https://doi.org/10.1016/j.geodrs.2021.e00392Get rights and content

Highlights

  • Medium-term eucalyptus cultivation maintains carbon, nitrogen stocks in the main soils of the Pampa Biome.

  • Biomass microbial are maintained with eucalyptus cultivation for a medium term in the Pampa Biome in southern Brazil.

  • Eucalyptus cultivation is a system that maintains soil quality in the soils of the South American Pampa biome.

Abstract

In the south of Brazil, the intensification of eucalyptus planting can impact the local biome, characterized by grasslands that extends to Uruguay and Argentina. Thus, the objective of the study was to evaluate changes in soil carbon, nitrogen and their labile fractions and soil microbiological attributes due to the introduction of eucalyptus cultivation in the Pampa biome. The soils evaluated were Eutric Regosol (RG), Haplic Lixisol (LX), Dystric Leptosol (LP) and Pellic Vertisol (VR). For this, areas of homogeneous cultivation of Eucalyptus saligna (7 years old) and areas of grassland (native vegetation) were selected. Physical granulometric fractionation of soil organic matter (SOM) was performed in the 0–5, 5–10 and 10–15 cm soil layers, quantifying levels, stocks and distribution of total organic carbon (TOC) and total nitrogen (TN) in the labile and associated with minerals fractions, and the carbon management index (CMI) was calculated. In the 0–5 and 5–10 cm soil layers, microbial biomass carbon (MBC), microbial biomass nitrogen (MBN), basal soil respiration, metabolic coefficient, MBC / TOC, MBN / TN, MBC / MBN ratios were also evaluated. Eucalyptus cultivation increased the TOC and POC carbon stocks by 8.7 and 21.7%, respectively (0-15 cm) in compared to grassland. It was also observed that the cultivation of eucalyptus increased 6.7% and 26.0% the stocks of TN and PN, respectively, compared to grassland in the pampa biome. Carbon stocks associated with minerals were not affected by eucalyptus cultivation. The cultivation of eucalyptus increased the basal respiration and the microbial biomass carbon in relation to grassland and there is a reduction of microbial biomass nitrogen in the soil. Thus, the cultivation of eucalyptus in the Pampa biome in southern Brazil demonstrates that it is a forest crop that can contribute to the increase in total and labile carbon stocks and also the biomass and microbial activity of the soil, which are important indicators of assessment of soil quality.

Section snippets

Introdution

Brazil leads the world ranking of forest productivity, contributing to an important part of the national economy (IBGE, 2018), generating products for internal consumption or for export (MAPA, 2018). Eucalyptus planting has expanded worldwide due to demand in wood and cellulose production, and Brazil is one of the main world producers, where eucalyptus is responsible for a cultivated area of 7.5 million ha (IBGE, 2018). The South of Brazil in the last 15 years received investments from

Characterization of the site and collected soil

The study was carried out in four different areas of the Pampa biome, with different soils types in each, classified as Eutric Regosol (loamic) (Area 1), Haplic Lixisol (loamic) (Area 2), Dystric Leptosol (loamic) (Area 3), and Pellic Vertisol (chernic, hypereutric) (Area 4). In each area, six soil profiles were sampled and characterized, three under eucalyptus vegetation cover and three under grassland (native vegetation), each three separated by 10 m. The soil profiles under the eucalyptus

Carbon distribution in the soil profiles

Table 2 shows the average TOC stocks of the soil in kg m−2 up to 50 cm, with the respective proportions in the 0–5, 0–10 and 0–20 cm layers in the areas of eucalyptus and grassland of the soils.

It is observed that there were no significant differences in carbon stocks in the 0–50 cm soil layer between soils covered with eucalyptus and grassland within the same area, but with differences between soils, being the stocks of VR higher. In the 0–5 cm layer, there were also no differences between the

Discussion

Little information is available about the effect of converting the Pampa biome into eucalyptus cultivation and the effects on soil TOC stocks. However, some studies have already been carried out in order to evaluate the TOC stocks in other Brazilian biomes followed by eucalyptus cultivation. Leite et al. (2010), when studying successive eucalyptus crops in Brazil, found lower soil organic matter values in eucalyptus areas, when compared to native forest areas. Fialho and Zinn (2014) found that

Conclusions

Eucalyptus cultivation in the Pampa biome in southern Brazil, after seven years, increases the total organic carbon and particulate organic carbon stocks by 8.7 and 21.7%, respectively, in the top layer of the soil (0–15 cm) in compared to grassland.

The cultivation of eucalyptus increases 6.7% and 26.0% the stocks of total nitrogen and particulate nitrogen, respectively, compared to grassland in the pampa biome.

Carbon stocks associated with minerals are not affected by eucalyptus cultivation in

Declaration of Competing Interest

The authors declare that there is no conflict of interest in this article.

Acknowledgements

To the soil science department of the Federal University of Pelotas for the financial support to carry out this research work.

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