all enzyme activities were higher in sewage sludge than in city refuse, at all times, denoting larger microbial populations; this was also confirmed by a high initial ATP level. In addition to differences in microbial biomass, the lower enzyme activity in city refuse might also depend on inhibition by a high content of heavy metals. Absolute urease and phosphatase activities decreased during composting, showing a minimum at 9l and 65 d, respectively; thereafter they increased slightly. ATP also decreased markedly during the first month, then it stabilized to a low level. The correlation found between ureasephosphatase-ATP and the lack ofcorrelation between proteases, and between both proteases and ATP-
A calcareous soil was treated with an organic fertilizer mixture of grape debris and peat, or with pig manure, chicken manure, city refuse or with aerobic or anaerobic sewage sludges. Changes in different fractions of carbon and nitrogen were followed by analysis of the soil, immediately after these additions, after they had decomposed for six months in the soil, after a maize harvest, and after a subsequent barley harvest.The various forms of carbon had decreased after six months. The rate of decrease varied with the nature of the organic materials. In all samples, the fulvic acids fraction decreased most. The main transformations happened during the first six months whether there was a crop growing or not, but the crops had no influence on the breakdown of the organic materials.The ratio of humic acids/fulvic acids had increased after six months of humification and, in general terms, the final values of the ratio oxidizable carbon/extractable carbon were lower than the initial ones, indicating a higher degree of humification in the organic matter by the end of the experiment.The total nitrogen level remained practically constant after the first six months of humification even after the second crop. Part of the organic nitrogen of the soil samples amended with chicken manure, city refuse or the two sludges was transformed into mineral nitrogen during the humification process. The extractable nitrogen values increased because of the fertilizer applied during the pot trials.
Para la simulación del carbono orgánico del suelo se utilizó el modelo RothC26.3 (Coleman y Jenkinson, 1999), que trabaja a una escala de tiempo mensual y permite determinar el recambio mensual del C mediante procesos cinéticos de primer orden, donde las tasas de descomposición de sus cuatro reservorios activos, son moduladas por la temperatura, la humedad y la cubierta de residuos. La investigación se realizó tomando como base la información de carbono orgánico del suelo y rendimientos agrícolas de experimentos desarrollados en áreas agrícolas de la Estación Provincial de Investigaciones de la Caña de Azúcar (EPICA) ubicada en Jovellanos, provincia Matanzas en el periodo comprendido entre 1981 y 2010. Los datos de carbono orgánico de la capa cultivable del suelo (0-20 cm), clasificado como Ferralsol plantado con caña de azúcar, correspondientes al ciclo caña planta, sirvieron de base para parametrizar el modelo, cuyo comportamiento fue modificado por las variables climáticas, procedentes de la estación meteorológica asociada al lugar. La comparación entre los datos de carbono orgánico del suelo simulados y los observados en el período 1981-2010, resultó en que los primeros expresaron 95,58% de la varianza de los datos experimentales. Se encontró que la cantidad necesaria de carbono orgánico para mantener el nivel que tenía el suelo en 1981fue de 6,28 t ha-1 año-1. Los resultados soportan el uso del modelo RothC26.3 como una herramienta para predecir el comportamiento del COS en condiciones tropicales.
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