Effect of vegetation on soil C, N, P and other minerals in Oxisols at the forest-savanna transition zone of central Africa

• Published in: Soil science and plant nutrition (Tokyo) 2014-01, Vol.60 (1), p.45-59
• Main Authors: Sugihara, Soh, Shibata, Makoto, Mvondo Ze, Antonie D, Araki, Shigeru, Funakawa, Shinya
• Format: Article
• Language: English
• Subjects: aluminum; bulk density; calcium; carbon; carbon nitrogen ratio; cation exchange capacity; clay fraction; climate change; forest soils; Forest-savanna transition zone; forests; fractionated phosphorus; iron; leaching; magnesium; minerals; nitrogen; Oxisols; phosphorus; potassium; savannas; sodium; sodium hydroxide; soil C:N ratio; soil density; soil depth; soil minerals; soil nutrients; soil pH; soil profiles; soil sampling; soil texture
• ISSN: 1747-0765; 0038-0768; 1747-0765
• DOI: 10.1080/00380768.2013.866523

The forest-savanna transition zone, which evolves as a result of past climate change, is widely distributed in central Africa. Because nutrient-poor soils (Oxisols) are widely distributed in this area, it is necessary to understand the characteristics of soil nutrients in relation to the vegetation. We collected 52 soil samples from five pits each for two different vegetation types (forest and savanna) in this area and evaluated the effect of vegetation type on soil physicochemical properties [pH, soil texture, cation-exchange capacity, bulk density, crystalline and non-crystalline aluminum (Al) and iron (Fe)] and nutrient status [carbon (C), nitrogen (N), phosphorus (P) and other soil minerals]. We also evaluated the fractionated P. Whereas most physicochemical properties were similar between the two vegetation types throughout the soil profile (0–80 cm depth), clay content, bulk density and soil pH clearly differed between the vegetations at the surface layer (0–10 cm). At 80 cm soil depth, soil C, N and P were 87.9, 7.7 and 3.7 Mg ha ⁻¹, respectively, in forest, and 98.6, 7.1 and 3.1 Mg ha ⁻¹, respectively, in savanna. Although there was no clear difference between the amounts of soil C, N and P, the upper-soil (0–40 cm) C:N ratio was clearly lower in forest (11.0–12.0) compared with savanna (13.0–15.7), because the main plant species in the forest can fix N effectively. We also found a smaller ratio of sodium hydroxide (NaOH)-extractable inorganic P to total soil P in forest compared with savanna. Because the content of crystalline and non-crystalline Al and Fe in forest soil was similar to that of savanna, the different soil C:N ratio would cause different availability of P between the vegetation types, although the mechanism is unclear. These results indicate that savanna vegetation is N-limited and forest vegetation is N-saturated (and possibly P-limited) in this zone. We also found that, at 20 cm soil depth, total soil potassium (K) in forest was 1590 kg ha ⁻¹, which was 930 kg ha ⁻¹ less than that in savanna (2520 kg ha ⁻¹; P