Resumo

RON, María de las Mercedes; MANDOLESI, María Ester; FACCHINETTI, Cecilia  e  JURGEN KIESSLING, Roberto. Anthropogenic effect on soil chemical fertility of a field in southwestern Buenos Aires. Cienc. suelo [online]. 2011, vol.29, n.2, pp.223-231. ISSN 1850-2067.

Soil cultivation produces negative soil fertility gradients from under the fence towards the center of a field, impacting distinctly the first cm of the arable layer. The objectives of this work are to quantify these gradients, in an establishment of Tornquist (province of Buenos Aires) and to evaluate the sensitivity of different soil quality indices. Three positions were selected in a field: 1) below the wire fence («alambre»); 2) 3-4 m from the fence («borde») and 3) 15 m from the fence («interior»). In each position, three composite samples were extracted, at two depths 0-6 and 0-12 cm. Soil samples were tested for pH; extractable phosphorus (P_BK) and boron (B_ext), total organic nitrogen (N_ot), exchangeable potassium (K_int), calcium (Ca_int) and magnesium (Mg_int). Determinations of organic carbon (CO) included total CO (COT) by dry combustion and oxidizable carbon (COX) by Walkley and Black (W-B). Fractions of CO of increasing oxidability were calculated from determinations using different concentrations of sulfuric acid. P_BK was the most variable soil test. The analyzed depths had a smaller impact on the variables than the positions, even after four years under no-till. pH, Ca_int and Mg_int did not decrease with agricultural use, confirming their stability in mixed systems of southwestern Buenos Aires. Some of the most sensitive indices (PBK, easily oxidizable CO) were positively associated. Losses of 43 and 490 kg ha^-1 of P_BK and K_int were estimated for the depth of 0-12 cm, representing 84% and 71% in the first six cm, respectively. COT diminished in one third in «interior». The rate of CO oxidation was significantly greater for «alambre» at 0-6 cm. The oxidation factor for W-B was of 0.82 «for interior» and 0.90 for «alambre» and «borde».

Palavras-chave : Soil degradation; Horizontal and vertical variability; Extractable nutrients; Organic carbon fractions.

        · resumo em Espanhol     · texto em Espanhol     · Espanhol ( pdf )