M. P. Jimenez

Litter fall and litter decomposition in a forest of the Parque Chaqueño Argentino

Abstract Amounts of litter produced by four species in a native forest in the Parque Chaqueno Argentino were registered monthly during a year. The species selected were Espina Corona (Gleditsia amorphoides (Griseb.) Taub), Gauyabi (Patagonula americana L.), Mora (Chlorophora tinctoria (L.) Gaud.) and Urunday (Astronium balansae Engl.). Espina Corona stands presented the highest contribution in total dry matter (13.5 kg ha−1); following in importance is Mora with 11.3 kg ha−1, Guayaibi with 9.8 kg ha−1 and Urunday with 8.8 kg ha−1. Mora leaves accounted for 8.3% of its total litter followed by Espina Corona with 8.1%, Guayaibi with 3.8% and Urunday with 2.8%. The rate of decomposition leaf litter was estimated according to the Olson model (single exponential). The species which presented the greatest average annual decomposition rate was Mora with k=0,28, significantly different (P≤0.05) to Espina Corona with k=0.16, and significantly different (P≤0.05) to the third group composed by Urunday (k=0.08) and Guayaibi (k=0.04). Espina Corona, Guayaibi and Urunday experimental data suggest that the dynamics of litter decomposition may be better described by a double exponential model with a fast decomposable fraction and a more resistant one. Mora leaf litter followed a different pattern, fitting to the single exponential model. From the present study it may be concluded that a more active biogeochemical cycle can be established for Mora followed by Espina Corona, Urunday and Guayaibi, given that, a greater decomposition rate means less time of nutrient retention by the litter.

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.

Potassium supplying capacity in Argentine soils and plant uptake rate

Abstract Exchangeable potassium (K) is the readily available form but when this pool is not sufficient, plants must be supplied from less labile forms of this nutrient. In this study, the contribution of nonexchangeable K to plant nutrition and the uptake rate of this nutrient in successive harvests were investigated. A greenhouse experiment was performed sowing annual ryegrass (Lolium multiflorum sp) on four agricultural soils with a wide range in exchangeable K concentration. The soils were a) Acuic Argiudol, b) Entic Hapludol, c) Typic Argiudol (Ordoñez and M. Juarez). Five harvests were conducted resowing after each one. Soil K extractable with 0.01 M CaCl2, exchangeable and nonexchangeable K was determined. Plant analyses were conducted to asses total K. The highest nonexchangeable K contribution to the total K uptaken by plants (in percentage) was observed in the Acuic Argiudol soil due to its low exchangeable K concentration. For the Typic Argiudol soils, this contribution varied according to exchangeable K concentration (Ordoñez soil) or according to the clay content and the mineralogy (M. Juarez). For all soils, the highest plant uptake rate was for the first harvests corresponding to the uptake of soluble K and the K located in the most labile positions in the exchange complex. This fact is confirmed by the high correlation obtained between the uptake rate and the amount of K extracted with CaCl2 (p<0.05). For subsequent harvests, a progressive decrease of K uptake rate was observed. In the fifth harvest plant uptake mostly depends on the nonexchangeable K concentration (p<0.05). The Acuic Argiudol soil, presents a special behavior • given that it reaches the minimum rate in the third harvest due to the low concentration of all K forms of this soil.

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.