Abstract

URIOSTE, Ana María; HEPPER, Estela Noemí; BELMONTE, Valeria  and  BUSCHIAZZO, Daniel Eduardo. Phosphorus fractions in soils of the Pampean Caldenal expose to different burn temperatures. Cienc. suelo [online]. 2009, vol.27, n.2, pp.177-183. ISSN 1850-2067.

Cattle production is one of the main productive activities in the Caldenal area of La Pampa Province, and burning is used to increase forage production. However, there are very few reports in the literature on the effect of controlled burning on soil phosphorus fraction content. The aim of this work was to analyze the effect of burn temperatures on organic and inorganic phosphorus fractions of a sandy loam and a loam soil. Superficial soil samples (0-5 cm) without plant cover were air dried and heated at 100, 200, 300, 400, 500 and 600 ºC, and a non-heated sample was left as control. In every sample, the P content was determined by a sequential extraction procedure using the following extractants: sodium bicarbonate (Pi-HCO₃), sodium hydroxide (Pi-NaOH and Po-NaOH) clorhidric acid (Pi-HCl) and sulfuric acid (P-H₂SO₄). In general, the effect of burn temperature on the analyzed fraction's content was similar in both soils. In general, heating at 300 ºC or higher temperatures increased Pi-HCO₃ and Pi-NaOH content and decreased P-H2SO₄ and Po-NaOH content, possibly due to organic matter decomposition at these temperatures and the consequent increase in available inorganic phosphorus. When soils were heated at 300ºC, increases in Pi-HCl content were registered in the sandy loam soil, whereas this fraction decreased in loam soil. Heating both soils at 600 ºC caused an increase in Pi-HCl related to higher pH values, indicating a decrease in Ca-phosphates. Burns involving soil temperatures no higher than 300 ºC do not produce changes in phosphorus fraction content. Heating at 300ºC produced a net decrease in P only in the loam soil, possibly due to the volatilization of organic materials.

Keywords : Soil temperature; Organic and inorganic phosphorus fractions; Caldenal soils.

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