Impact of forest–pasture conversion on soil physical and chemical attributes

Abstract

The objective of this paper is to assess the changes in soil physical and chemical attributes resulting from the conversion of native forest to pasture and pasture to secondary forest in the state of Santa Catarina, Brazil. Seven forest–pasture successional stages were identified using aerial photographs and satellite images acquired in 1957, 1978, and 2008. Successional stages were coded as FFF, FPF, PFF, PPF, FPP, FFP, and PPP, where the first, second, and third letters refer to the land uses (P, pasture; F, forest) practiced in 1957, 1978, and 2008, respectively. Soil samples were collected by layer at depths of 0–10, 10–20, 20–40, 40–60, 60–80, and 80–100 cm. Clay contents, soil bulk density (D_b), macroporosity (MP), microporosity (mP), pH, calcium (Ca), potassium (K), phosphorus (P), total organic carbon (TOC) content, carbon stock, and δ¹³C abundance were quantified. Conversion of forest to pasture increased soil P, K, Ca, D_b, and mP; and reduced TOC content and carbon stocks. The largest carbon stocks occurred in sites occupied by forest but previously used as pasture. Forest and pasture age influenced δ¹³C values, resulting in different isotopic signatures for different sites and confirming the transition from C₃ to C₄ plants. In 50-year-old pastures, about 66% of soil TOC is still derived from the primary forest biomass.