Abstract The release kinetics of nitrogen and phosphorous of a granulated fertilizer, encapsulated in a κ-carrageenan-based hydrogel (CBH), was evaluated in order to determine its release mechanism given the potential this hydrogel has as coating material for controlled release fertilizers (CFRs). The effect of pH on the release properties was also investigated. The relationship between the NH4+, NO3-, and PO43- release of encapsulated fertilizers and time was determined by short- and long-term laboratory incubations. The mechanism of the release of nutrient ions was determined by comparing the release data with the zero-order, first-order, Higuchi, Hixon-Crowell and Korsmeyer-Peppas kinetic models. The findings showed that the Korsmeyer-Peppas model could be used to describe the release characteristics of the nutrients in the encapsulated fertilizers and that non-Fickian diffusion is the main release mechanism. The experimental hydrogel showed a high water retention capacity able to absorb 300 times its weight water.

ABSTRACT Microorganisms are excellent soil quality indicators because their properties within the soil community change quickly in response to changes in the surrounding environment. The aim of this study was to determine if the structure and diversity of soil bacterial and fungal communities were useful for discriminating cut flower cultures under conventional (CM), ecological (EM), and intermediate (IM) management practices. Results obtained by PCR-DGGE revealed that bacteria had lower similarity in structure and higher diversity under EM than under CM. Sites under IM showed greater similarities in structure and diversity to the site under CM, although there were still significant differences between them. Fungal structure showed higher similarity among sites, with differences in diversity only between EM and CM. In the sites studied, bacteria, rather than fungi, were good indicators of changes in soil quality. The results of this study confirmed that EM and IM promote soil bacteria diversity.

En agregados de nieve marina influenciada por escorrentía continental, la densidad de bacterias heterótrofas es mayor que la de autótrofas. Esta premisa fue puesta a prueba en cuatro zonas arrecifales localizadas a diferente distancia del Canal del Dique; principal fuente de aportes continentales a los arrecifes de coral del Archipiélago Nuestra Señora del Rosario, Cartagena, Caribe colombiano. Mediante epifluorescencia se determinó densidad promedio de microorganismos presentes en agregados de nieve marina. Los resultados mostraron mayor densidad de bacterias heterótrofas (3.63 x 10(4) ± 1.6 x 10(4) SE células mL-1) que de autótrofas (6 x 10³± 1.3 x 10³ SE células mL-1), principalmente en arrecifes cercanos a descarga de escorrentía continental (bacterias heterótrofas con densidad 8.9 x 10(4) células mL-1 y 3 x 10(4) células mL-1 para Isla Arena y Tesoro, respectivamente). La densidad de microorganismos encontrada es típica de zonas con alto contenido de materia orgánica particulada; por lo cual podría servir como potencial indicador de escorrentía continental. Estudios futuros deben enfocarse en determinar la composición de comunidad bacteriana asociada a nieve marina y posible virulencia sobre organismos arrecifales.

The density of heterotrophic bacteria is greater than autotrophic in marine snow aggregates influenced by continental runoff. Four coral reef areas at different distances from the Canal del Dique served to evaluate this premise; this canal is the main source of inland resources for the coral reefs of the Nuestra Señora del Rosario archipelago in Cartagena in the Colombian Caribbean. The average density of microorganisms in marine snow aggregates was determined using epifluorescence. The results showed higher density of heterotrophic bacteria (3.63 x 10(4) ± 1.6 x 10(4) SE cells mL-1) than autotrophic (6 x 10³± 1.3 x 10³ SE cells mL-1), mainly in reefs near continental runoff discharges (heterotrophic bacteria density of 8.9 x 10(4) cells mL-1 and 3 x 10(4) cells mL-1 Isla Arena and Tesoro, respectively). The density of microorganisms found is typical of high-particulate organic matter areas and, therefore, could be a potential indicator of continental runoff. Future studies should focus on determining the composition of the bacterial community associated with marine snow and its potential virulence on reef organisms.

Em aglomerados de neve marinha influenciados por escoamento continental, a densidade de bacterias heterotróficas é maior que a de autótrofas. Esta premissa foi posta a prova em quatro zonas de recifes localizadas em diferentes distancias do Canal de Dique; principal fonte de contribuic.ao continental aos recifes do coral do Arquipélago Nossa Senhora do Rosàrio, Cartagena, Caribe colombiano. Mediante epifluorescencia determinou-se densidade de micro-organismos presentes em aglomerados de neve marinha. Os resultados mostraram maior densidade de bacterias heterotróficas (3.63 x 10(4) ± 1.6 x 10(4) SE células mL-1) que de autótrofas (6 x 10³ ± 1.3 x 10³ SE células mL-1), principalmente em recifes próximos a descarga de escoamento continental (bacterias heterotróficas com densidade 8.9 x 10(4) células mL-1 y 3 x 10(4) células mL-1 para a Ilha Arena e Tesoro, respetivamente). A densidade de micro-organismos é típica de zonas com elevado conteúdo de matéria orgànica particulada; pela qual pode servir como potencial indicador de escoamento continental. Estudos futuros devem enfocar-se em determinar a composicäo da comunidade bacteriana associada a neve marinha e possível virulencia sobre organismos recifais.

This study assessed the presence of tetracycline-resistant bacteria in five different grassland-based production systems dedicated to raising dairy cattle located in the Colombian Andes. Animal (ruminal fluid and feces) and environmental (soil and water) samples were evaluated, and resistant heterotrophic bacteria were found in rumen fluid, feces, soil, and runoff water samples. The resistant bacteria were isolated and identified based on the 16S rDNA region. Subsequently, they were evaluated for the presence of tet genes, which encode ribosomal protection proteins and membrane efflux pumps. The most frequent phyla detected were Firmicutes and Proteobacteria. The most common resistance genes found were tet(W), tet(Q), and tet(M). The nucleotide sequences of the genes showed no differences in bacteria isolated from environmental samples versus ruminal fluid and feces. This result suggests that the observed environmental resistance in the evaluated grasslands is the result of horizontal gene transfer from animals to the environment.

En este estudio se evaluó la presencia de reservorios ambientales y animales de bacterias resistentes a la oxitetraciclina (OTC) en cinco sistemas de producción extensivo dedicados a la cría de ganado lechero y localizados en el Altiplano Cundiboyacense. Los tamaños poblacionales de las bacterias heterótrofas resistentes, estimados en muestras ambientales (suelo y agua) y animales (líquido ruminal y estiérco) mediante técnicas de cultivo, fueron notables especialmente en muestras de líquido ruminal, estiércol, suelo y agua de escorrentía. Bacterias resistentes fueron aisladas, identificadas mediante la región 16S ADNr y evaluadas para la presencia de genes tet que confieren resistencia a la tetraciclina y que codifican para proteínas de protección ribosomal y proteínas membranales de eflujo. Los filos más comunes dentro de las 140 cepas aisladas fueron Firmicutes y Proteobacteria dentro de las cuales se encontraron géneros típicos tanto del ambiente como del tracto intestinal. Los genes de resistencia más comunes fueron tet(W), tet(Q) y tet(M) y la comparación entre sus secuencias no muestran diferencias entre genes de bacterias aisladas del ambiente y bacterias del tracto digestivo de los animales, lo que sugiere que los reservorios de resistencia en el ambiente son el resultado de la transferencia horizontal de genes desde las bacterias resistentes de los reservorios animales.

Se determinaron las concentraciones y los porcentajes de reabsorción de nitrógeno y fósforo foliar en cinco especies de árboles de un bosque montano bajo (BMB) a 1850 m.s.n.m. y en cinco de un bosque montano alto (BMA) a 2800 m.s.n.m en la Cordillera Central colombiana, asi como la disponibilidad de nitrógeno y fósforo del suelo. Los porcentajes de reabsorción de N y P no fueron significativamente diferentes entre las especies de estos dos bosques. A pesar de esto, se observó que la reabsorción de P foliar tendió a ser mayor en las especies del BMB donde la concentración de P en el suelo fue significativamente más baja (3.2 ppm vs. 9.0 ppm). Cuando la reabsorción de P foliar se expresó como función de la concentración en hojas maduras en 12 tipos de bosques montanos tropicales, se encontró una correlación negativa y estadísticamente significativa. Estos resultados sugieren que los porcentajes de reabsorción de P foliar en bosques montanos estarían controlados parcialmente por la disponibilidad del elemento.

Mature leaves and litterfall were collected between November 1992 and February 1993 from one to three individuals of five canopy tree species of a lower montane rain forest (LMRF) at 1850 m. and five canopy tree species of an upper montane rain forest (UMRF) at 2800 m. in the Central Andes of Colombia, to determine the concentrations and percentage retranslocation of nitrogen and phosphorus. The availability of these two nutrients was measured in the soils, by means of extracts of NH3-NH4, NO2-NO3 and PO4, and incubations of surface soil samples (0-10 cm) to measure the rates of nitrogen mineralization and nitrification. In the species of the LMRF the average concentration of N in mature leaves (1.19 % dry weight) and litterfall (0.87 %) was significantly higher than in mature leaves (0.90 %) and litterfall (0.59 %) of the tree species of the UMRF. Percentage retranslocation of N and P were not significantly different between the species of these two forests. In spite of this, P retranslocation tended to be higher in the species of the LMRF where the available P in the soil was significantly lower (3.2 ppm vs. 9.0 ppm). A negative and statistically significant correlation was found between the percentage retranslocation of P and the concentration of this element in mature leaves of 12 different tropical montane forests. These results suggest that percentage retranslocation of foliar P in montane forests, could be partially controlled by the availability of this element. There were no statistically significant correlations between percentage retranslocation of N and P and specific leaf area for the ten tree species of this study. The lack of correlation may be the result of a small sample size and should be explored with a higher number of species.