Nilda Marta Arrigo

Chemical and biochemical properties as potential indicators of disturbances.

Abstract The response of a series of soil microbial, chemical, and enzymatic chacacteristics to two different tillage systems (conventional and no-tillage) and two crop rotations (continuous corn and soybean–corn) was evaluated in a long-term field experiment in the Rolling Pampas Region, Marcos Juárez, Córdoba, Argentina. The parameters studied included: oxidizable, soluble and respiration C, total and hydrolyzable N, microbial activity, ammonifiers, nitrifiers, cellulolytic and total microflora, protease and urease activities. After 15 years, oxidizable C, total N and hydrolyzable N showed no differences regarding no-tillage systems. However, differences were found regarding control soil. While soluble C did not exhibit any significant differences, respiration C and microbial activity were indicators sensitive to different treatments. Enzymatic activities, protease in particular, did reflect changes due to management. Fluctuation in microbial population counts were more related to plant residues than to tillage systems.

Relationship of soil carbon light fraction, microbial activity, humic acid production and nitrogen fertilization in the decaying process of corn stubble

Abstract The variation in stubble decomposition due to fertilizer incorporation was determined in a typical Argiudoll of the Argentinian rolling pampas. The experiment was conducted for 15 years, which included a no till system under maize (Zea mays L.) and a soybean rotation (Glycine max) with 0 and 45kg N ha–1 nitrogen fertilization treatments, called NFS and FS, respectively. A higher proportion of residues with a high N content was found in the FS plots. The different substrate quality proved to be the regulating factor for mineralization. This activity was indicated by the increase in soil microbial activity and soil carbon light fraction in FS compared to NFS. This carbon light fraction mineralizes rapidly but does not contribute to the most stable components, which are related to synthesis and polymerization of humic acids. No significant differences in humic acid content were found.

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.