D. Effron

Effect of Cadmium, Copper, and Lead on Different Enzyme Activities in a Native Forest Soil

Abstract Heavy metals contamination has been reported to affect enzymatic activities in soils. The objectives of this work were (i) to study the effect of cadmium [Cd(II)], copper [Cu(II)], and lead [Pb(II)] at different doses and different incubation times on arylsulphatase, ß-glucosidase, acid phosphatase, protease, and urease activities in a noncontaminated native forest soil and (ii) to analyze the potential use of enzyme activity to detect contamination in soils by the studied metals. The study site was located in a subtropical forest of Argentine. A soil sample representative from the studied site was placed in plastic containers and contaminated with solutions containing Cd (20, 100, 200, and 500 mg kg−1 soil), Cu (50, 250, 500, and 2500 mg kg−1 soil), and Pb (40, 200, 400, and 1000 mg kg−1 soil) in a laboratory experiment. The metal influence on the enzymatic activity was studied at different incubation times (30, 60, 90, and 120 days). Results showed that, the metals studied inhibited the arylsuphatase, acid phosphatase, protease, and urease activities. Little or no effect was detected on the ß-glucosidase activity. The toxicity of the different metals evaluated through inhibition percentage of the enzyme activities was in the order Cd ≅ Cu > Pb. It may be concluded that protease was the enzyme more sensitive to indicate the soil pollution caused by the studied metals in this ecosystem.

Factors affecting potassium fixation in Argentine agricultural soils

Potassium (K) fixation in Argentine soils and its effects on fertilizer K dose effectiveness remains an under-researched topic. The effects of K addition doses and clay type and content on the K fixation/release dynamics of added K in four soils, two Argiudols, an Ultisol and an Andisol were studied. Fixation responded to soil type, but not to K doses. From 5 to 24% of the applied K was fixed by the soils ranking from highest to lowest: Aquic Argiudol, Typic Palehumult, Typic Udivitrand and Typic Argiudol. The trend for K fixation relative to clay content was reversed. The soils fixed between 0.23 and 2.38 (cmolc kg−1) (g clay)− 1 in increasing order: Typic Argiudol, Typic Palehumult, Aquic Argiudol and Typic Udivitrand. Potassium fixation by occlusion in clay pores could account for the high activity of the Andisol. The Q/I isotherms results were consistent with those from the fixation experiment. The residuality index, B, ranged from 0.65 (Aquic Argiudol) to 0.95 (Typic Argiudol), a trend consistent with K fixation by these soils. Exchangeable K measured in the fertilized soils and calculated through the residuality index was highly correlated (r=0.95; p < 0.01). This study shows that the B index is a useful tool in quantifying the potential of contrasting soils for net K fixation and in adjusting K rates to accommodate for this process.

Foliar potassium, calcium, magnesium, zinc, and manganese content in soybean cultivars at different stages of development

Abstract Plant tissue accumulation of potassium (K), calcium (Ca), magnesium (Mg), zinc (Zn), and manganese (Mn) was determined for six soybean [Glycine max (L.) Merr.] cultivars at successive stages of development. No nutrient accumulation patterns among the cultivars were found. The results obtained showed that the highest concentrations of K were found at the vegetative stage (V) and the lowest towards the end of the life cycle of the plant (R55). By contrast, Ca was lowest at the vegetative stage while increasing in the leaves in later growth stages. No significant differences in Mg content were found between growth stages. Manganese levels were lower at R2 and R4 than at R55 stages of growth with an accumulation towards the end of the reproductive cycle. Changes in Zn content between stages were different for each cultivar. The differing behavior of these elements is related to the difference in their mobility and transport capacities within the plant.

Effect of potassium fertilizers on quantity‐intensity parameters in some argentine soils

Abstract The parameters obtained from the quantity‐intensity (Q/I) isotherms have been used by several authors as criteria to estimate the immediate availability of labile potassium (K) in a soil. The aim of this work was to study how these parameters have been modified in four agricultural soils in Argentina by the addition of K (0 to 936 kg K2O ha‐1) in an incubation trial simulating K fertilizers application. In two of the soils, the increase in the labile forms of K was proportional to the amount of added K and the recovery percentages were high. In the other soils, a contrasting behavior was found. This difference might be due to different fixing capacity of the soils, which was related to the clay content and mineralogical composition of this fraction. The slopes of the Q/I curves for each soil indicate that the potential buffer capacity (PBC) was similar for the different treatments over the range of K added. The addition of K produced proportional increases in ARe and ?Ko values. This could be att...

CARBONO DE RESPIRACIÓN DE UN SUELO FORESTAL Y SU RELACIÓN CON LA CALIDAD DE LA HOJARASCA

Este estudio busca determinar las ventajas relativas de una cosecha mecanica de uva vinifera en comparacion con la cosecha manual. Durante las vendimias de los anos 1998 y 1999 se recogieron 20 muestras directamente de la tolva de una vendimiadora automotriz e igual numero de muestras de las gamelas de cosechadores manuales, con el fin de analizar la calidad de la fruta que llegaba a la bodega con cada uno de estos sistemas de cosecha. Adicionalmente se tomaron datos de terreno relativos a la eficiencia de trabajo tanto de la vendimiadora como de cosechadores manuales. Todos estos datos se complementaron con muestras de cosechadora mecanica y de cosecha manual tomadas el mismo dia en un mismo cuartel en la vendimia del ano 2000, con el fin de hacer microvinificacion y comparar los vinos resultantes. El estudio concluyo que la calidad de la materia prima cosechada con vendimiadora automotriz es menor que la obtenida mediante cosecha manual. No obstante, los vinos resultantes de ambos sistemas de cosecha son de calidad equivalente, aunque distinguibles por degustadores especializados. Una hora de vendimiadora automotriz, operada en la forma observada en los predios estudiados, permite reemplazar a 70,0 horas-hombre. No obstante, se observo que esta maquina esta siendo trabajada fuera de la norma que establece la literatura especializada. Si se ajustara a la norma, la tasa de sustitucion seria de solo 37,3 horas-hombre. El tamano minimo de plantacion que justifica la adquisicion de una vendimiadora automotriz es de 140 hectareas.

Biochemical and microbiological properties of Argentinean Patagonia soil with implanted forest species

The aim of the present study was to determine the effect of two implanted forest species with different vegetal residue chemical compositions on the biological and biochemical properties of soil. The study site was located in the INTA Forestal Station of Trevelin, Chubut, Argentina. Samples were extracted from soil in forest plots dominated by Radiata Pine (Pinus radiata D. Don.) or European Ash (Fraxinus excelsior L.). Microbial respiration, dehydrogenase activity, community-level physiological profile (CLPP) and index of microbial community functional diversity were used as biological parameters; and acid phosphatase, protease and β-glucosidase activities were employed as biochemical parameters. Microbial respiration, dehydrogenase and acid phosphatase activities showed greater values in soil under European Ash trees; however, significant differences in protease and β-glucosidase activities were not observed among species. The higher organic C content of soil under European Ash trees and lower lignin and greater N and P content of the leaves of European Ash trees could be responsible for the greater biological and biochemical activities observed in the soil. Principal component analysis (for PC1) showed significant differences in the physiology of microbial communities associated with these forest species. The Shannon-Weaver Index (H) of the functional diversity of microflora did not present significant differences among forest species.

Niveles de Glomalina en un suelo con plantaciones de Pino radiata ( Pinus radiata D. Don.) y distintos tiempos de plantación

Los hongos micorrizicos arbusculares (HMA) son microorganismos simbiontes que forman asociaciones mutualisticas con raices de la mayoria de las plantas superiores. Los HMA producen glomalina que contiene un alto porcentaje de carbono y su contenido puede usarse como un indicador de los efectos del cambio de uso del suelo. El objetivo de este estudio fue evaluar el contenido de glomalina total (GT) y glomalina facilmente extraible (GFE) en un suelo andisol de la Provincia de Chubut, Argentina, bajo la influencia de la especie forestal ( Pinus radiata D. Don. en dos parcelas con diferentes tiempos de plantacion, una con 50 anos (P50) y otra con 20 anos (P20); y vincular dichos niveles con el carbono organico, las propiedades biologicas y bioquimicas del suelo. Los resultados mostraron que los valores de los parametros dosados dependieron del tiempo de plantacion, resultando significativamente mayores en el suelo con la plantacion de 50 anos. Los mayores valores del C de respiracion y de las actividades enzimaticas en el suelo bajo P50 podrian vincularse con los mayores niveles de glomalina hallados, ya que la misma, al influir en el mejoramiento de los agregados del suelo y generar un aumento en el contenido de C organico, causaria en el mismo un incremento en la actividad microbiana del suelo.

Influencia de Especies Arbóreas Implantadas sobre Parámetros Biológicos y Bioquímicos en un Suelo Forestal de Chubut, Argentina

The influence of some tree species on biological and biochemical properties of a forest soil was studied with the purpose of establishing criteria to achieve a sustainable development of a forest system. The study site is a forest soil of Chubut, in the Argentinean Patagonia. Surface soil samples were taken of three plots with a dominant species each one: Oak (Quercus robur), Ash (Fraxinus excelsior L.) and Radiata Pine (Pinus radiata D. Don.). Microbial respiration, dehydrogenase and acid phosphatase activities, counts of aerobic and amylolytic bacteria, actinomyces and fungi were determined in soil samples, while phosphorous was determines in leaves. The results showed important differences of these parameters for the different species considered in the study, differences that are explained by the different chemical composition of the vegetal species.

Relación de la Actividad de Fosfatasa Ácida con Especies Forestales Dominantes y con Algunas Propiedades del Suelo de un Bosque Argentino

Se estudio la influencia de las especies forestales dominantes sobre la actividad de fosfatasa acida y su vinculacion con el contenido de carbono organico y de fosforo disponible en un suelo de bosque. Las muestras de suelos fueron extraidas de debajo de arboles de cuatro especies en dicho bosque: Espina Corona [Gleditsia amorphoides (Griseb.) Taub.], Guayaibi (Patagonula americana L.), Mora [Chlorophora tinctoria (L.) Gaud.] o Urunday (Astronium balansae Engl.). La actividad de la enzima y el contenido de carbono organico presentaron valores mas altos debajo de Espina Corona y Mora. Se encontro una correlacion positiva significativa entre el contenido de carbono organico y el fosforo disponible y los valores de fosforo disponible no presentaron diferencias significativas entre especies. El menor coeficiente de correlacion encontrado entre el fosforo disponible y la actividad de la enzima indicaria que la actividad de la misma respondio fundamentalmente a las diferencias en contenido de carbono en el suelo generadas por las diferentes especies forestales.