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The effects of stand age, site index and parent material on soil biochemical properties related to biomass (extractable C, microbial C and metabolic quotient) were examined in the 0-15 cm mineral soil layers of Pinus pinaster and Pinus sylvestris stands from NW Spain. Two productivity levels (low and high site index), two ages (young and old) and two parent soil materials (granite and acid schists) were considered. The data indicated that there were differences in microbial parameters in soils under different species. In general in P. pinaster forest higher values of biochemical parameters, expressed on organic C basis, were observed in the stands of high site index as compared with the low ones; in contrast, in P. sylvestris no differences among stand site index were detected. In both species different results were also observed depending on parent material and a significant effect of stand age was detected for extractable C and microbial C in P. pinaster forest developed over granite. The data seem to indicate that measured parameters may have the potential to be used as indicators of the effect of forest management on soil organic matter quality.Key words: Microbial C, extractable C, metabolic quotient, reforestation, Pinus pinaster, Pinus sylvestris. ResumenBiomasa microbiana edáfica en pinares del noroeste de España: influencia de la edad de la plantación, índice de sitio y material de partida Se examina la influencia de la edad de la plantación, índice de sitio y material de partida sobre las propiedades bioquímicas relacionadas con la biomasa microbiana (C extraíble, C microbiano y coeficiente metabólico) del horizonte superficial de suelo (0-15 cm) de plantaciones de Pinus pinaster y Pinus sylvestris del Noroeste de España. Se consideraron dos índices de sitio (baja y alta calidad), dos edades de plantación (joven y vieja) y dos materiales de partida (granito y esquistos). Los datos indicaban que hubo diferencias entre los parámetros microbianos de suelos bajo diferente vegetación. En general, para P. pinaster se observaron valores más altos de los parámetros bioquímicos, expresados en base al contenido de C orgánico, en las plantaciones de alta calidad que en las de baja calidad; por el contrario en las plantaciones de P. sylvestris no se detectaron diferencias con respecto al índice de sitio. En las plantaciones de ambas especies se observaron resultados diferentes dependiendo del material de partida y también se observó un efecto significativo de la edad de la plantación sobre el C extraíble y el C microbiano en suelos desarrollados sobre granito bajo P. Pinaster. Los resultados parecen indicar que las propiedades bioquímicas medidas pueden ser utilizadas como indicadores del efecto del manejo forestal sobre la calidad de la materia orgánica del suelo.Palabras clave: C microbiano, C extraíble, coeficiente metabólico, plantación forestal, Pinus pinaster, Pinus sylvestris.

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Extractable atrazine and its metabolites (hydroxyatrazine, deethylatrazine and deisopropylatrazine) were evaluated in agricultural soils from the temperate humid zone (Galicia, NW Spain) under laboratory conditions. The experiment was performed with five soils with different properties (organic C, soil texture and atrazine application history), both unamended and treated with atrazine at field application rate. Measurements of the atrazine compounds were made at different time intervals (1, 3, 6, 9 and 12 weeks) during a 3-month incubation period. Results showed that only hydroxyatrazine was detected in the extractable fraction of the unamended soils, with values remaining relatively constant throughout the incubation period. Atrazine addition notably increased the concentration of the parent compound and its degradation products; deisopropylatrazine and hydroxyatrazine were the main metabolites detected in the extractable fraction of the treated soils, whereas deethylatrazine was not detected. After 7 days incubation, values of total extractable residues, expressed as percentage of initially added atrazine, ranged from 75 to 86% (25-68% of atrazine, 7-11% of hydroxyatrazine and 9-57% of deisopropylatrazine). The values decreased rapidly during the first 3 weeks of incubation, showing values of 2-8% in soils with higher atrazine application and from 28 to 30% in soils with lower application history. At the end of the incubation, 2-8% of total extractable residues were still detected (0-4% of atrazine, 2-3% of hydroxyatrazine and 0-2% of deisopropylatrazine), indicating a residual effect of atrazine addition. These variations in the extractable fraction indicated that most added atrazine was rapidly degraded, especially in soils with higher application history.