Balances de elementos en un agroecosistema de caña de azúcar: II. Balance de Fósforo

The paper considers the application of the studies of nutrient cycling on the determination of phosphorus requirements in sugarcane plantations. The work was performed in a 4.5 ha experimental plot located in the valley of Yaracuy river in central, Venezuela. The plot was planted with the varieties Puerto Rico (PR) 1028 and Venezuela (V) 58-4. The principal flows of phosphorus, as well the quantities of this element in the soil-plant components were measured throughout the growing cycle of the crop (second ratoon). The inputs through precipitation (wet and dry) were high, that was associated with the intense agricultural (prescribed burning of sugarcane plantation) and industrial activities occurring in the area. The annual balance for both varieties was negative (-17 and - 23.3 kg.ha-1 for V 58-4 and PR 1028, respectively). The negative budget is mainly due to the important amounts of P that are exported with the cane stems. The losses must be compensated though fertilisation, nonetheless, preliminary results indicated no response to P dressing, suggesting that in the studied mollisol the internal processes e.g. Po mineralization and P solubilization, efficiently operate generating important available P levels. It was also found that the burning of the sugar cane plantation plays an important role in the recycling of phosphorus, since 25-30% of the P requirements of the varieties are reincorporated into the soil from the ashes

Balances de elementos en un agroecosistema de caña de azúcar: I. Balance de nitrógeno

In a tropical mollisol cropped with sugar cane the annual nitrogen balance was quantified taken into account the main i) inputs, ii) outputs and iii) transference of the element (N-NO3 + N-NH4) in the plant and soil subsystems. Precipitation input corresponded to 26.3 kg N.h–1.yr-1 mainly as N-NH4. After the rain water passes the sugar cane canopy there was a retention of N in the N-NH4 form, whereas N-NO3 was leached from the canopy. Outputs through leaching reached 5.3 kg N. ha-1.yr–1 mainly as N-NO3. An important part of total soil N is fixed to the 2:1 type clay particles (montmorillonitic), abundant in the studied mollisol. It is hypothesised that this fixed N could act as a soil N reserve. Net mineralization of the organic-N reached a high value (343 kg N.ha-1.yr–1) in accordance with the intense nitrification process occurring in the soil as a consequence of the convenient C/N ratio and urea fertilisation. Major N losses in the agrosystem correspond to cropping export and removal of ashes after fire. Yearly 98% of N accumulated in the aerial biomass is lost through those ways. In general the annual nitrogen budget is driven off through input by fertilisation and output through stem cropping and N volatilisation by fire

Birth, death and diffusion of interacting particles

Individual-based models of chemical or biological dynamics usually consider individual entities diffusing in space and performing a birth-death type dynamics. In this work we study the properties of a model in this class where the birth dynamics is mediated by the local, within a given distance, density of particles. Groups of individuals are formed in the system and in this paper we concentrate on the study of the properties of these clusters (lifetime, size, and collective diffusion). In particular, in the limit of the interaction distance approaching the system size, a unique cluster appears which helps to understand and characterize the clustering dynamics of the model.Comment: 15 pages, 6 figures, Iop style. To appear in Journal of Physics A: Condensed matte

El reto de la conciliación trabajo y familia ¿qué nos estamos jugando?

Las dificultades que tienen las personas para encontrar el equilibrio entre su familia y su trabajo profesional son una marca de identidad de la realidad social española actual. En el proceso de cambio social que se ha producido de una forma vertiginosa en el último siglo, junto a los grandes avances que han hecho, sin duda, más fácil la vida a las personas, la confrontación familia-trabajo que actualmente se vive en muchas familias es una de las sombras que ha acompañado a estas transformaciones. Aunque la conciliación sea un reto global en la Unión Europea, e incluso podemos extenderlo a muchas otras regiones del mundo, las dificultades difieren mucho de unos países a otros, y España, junto con el resto de países de arco Mediterráneo, vive una situación especialmente complicada en el entorno europeo. Una muestra de esta preocupación se aprecia al comprobar que 2014 fue designado como el año europeo para la reconciliación de la vida laboral y familiar. El objetivo de este trabajo es dibujar un marco de comprensión amplio que ayude a entender la importancia del tema resaltando las implicaciones que tiene la no conciliación pero también los grandes beneficios que resultan de encontrar el equilibrio y la armonía entre la vida familiar y la laboral. El texto se articula en tres partes: i) las razones que explican que la conciliación sea en la actualidad especialmente uno de los grandes retos que tiene la sociedad; ii) las razones que hacen necesario que se articulen estrategias para superar este reto y los agentes que tienen un papel protagonista a la hora de potenciar y llevar a cabo estas estrategias; y iii) las estrategias o las respuestas ante los problemas de conciliación

Spontaneous Symmetry Breakdown in non-relativistic Quantum Mechanics

The advantages and disadvantages of some pedagogical non-relativistic quantum-mechanical models, used to illustrate spontaneous symmetry breakdown, are discussed. A simple quantum-mechanical toy model (a spinor on the line, subject to a magnetostatic interaction) is presented, that exhibits the spontaneous breakdown of an internal symmetry.Comment: 19 pages, 5 figures. arXiv admin note: substantial text overlap with arXiv:1111.1213. Equations (30) and (31) have been corrected. Other minor correction

Crystallization and melting of bacteria colonies and Brownian Bugs

Motivated by the existence of remarkably ordered cluster arrays of bacteria colonies growing in Petri dishes and related problems, we study the spontaneous emergence of clustering and patterns in a simple nonequilibrium system: the individual-based interacting Brownian bug model. We map this discrete model into a continuous Langevin equation which is the starting point for our extensive numerical analyses. For the two-dimensional case we report on the spontaneous generation of localized clusters of activity as well as a melting/freezing transition from a disordered or isotropic phase to an ordered one characterized by hexagonal patterns. We study in detail the analogies and differences with the well-established Kosterlitz-Thouless-Halperin-Nelson-Young theory of equilibrium melting, as well as with another competing theory. For that, we study translational and orientational correlations and perform a careful defect analysis. We find a non standard one-stage, defect-mediated, transition whose nature is only partially elucidated.Comment: 13 Figures. 14 pages. Submitted to Phys. Rev.