Ground cover and leaf area index relationship in a grass, legume and crucifer crop

Canopy characterization is essential for describing the interaction of a crop with its environment. The goal of this work was to determine the relationship between leaf area index (LAI) and ground cover (GC) in a grass, a legume and a crucifer crop, and to assess the feasibility of using these relationships as well as LAI-2000 readings to estimate LAI. Twelve plots were sown with either barley (Hordeum vulgare L.), vetch (Vicia sativa L.), or rape (Brassica napus L.). On 10 sampling dates the LAI (both direct and LAI-2000 estimations), fraction intercepted of photosynthetically active radiation (FIPAR) and GC were measured. Linear and quadratic models fitted to the relationship between the GC and LAI for all of the crops, but they reached a plateau in the grass when the LAI mayor que 4. Before reaching full cover, the slope of the linear relationship between both variables was within the range of 0.025 to 0.030. The LAI-2000 readings were linearly correlated with the LAI but they tended to overestimation. Corrections based on the clumping effect reduced the root mean square error of the estimated LAI from the LAI-2000 readings from 1.2 to less than 0.50 for the crucifer and the legume, but were not effective for barley.

Mapa preliminar de períodos predominantes del suelo en Puerto Príncipe (Haití) a partir de medidas de ruido ambiental.

The 2010 Haiti earthquake, occurred on January 12th at 16:53:09 local time (21:53:09 UTC) with epicentral distance of 15 km from the capital Port au Prince, MW 7.0 and 13 km hypocenter deep, was the strongest event in the area since happened in 1770. The maximum macroseismic intensity was estimated as X (MMI scale). The aim of this research is to obtain a preliminary zonation of Port-au-Prince in terms of predominant resonance periods of ground. A total of 36 short-period ambient noise records have been carried out on a grid of about 500x500m. H/V spectral ratio method (HVSR) has been applied to determine the predominant period at each point. The lowest values (<0.2s) predominate in the southern part of the city, composed by Miocene conglomerates, while highest values (> 0.45s) correspond to the center and western parts, composed of Pleistocene-Holocene alluvial deposits and anthropogenic land reclaimed from the sea. We have determined the ground VS30 structure inside National Palace garden, using simultaneous ambient noise measurements. An array made up of 6 sensors were used, with 5 of them uniformly distributed along a circumference and a sixth one placed in its centre. The records were analyzed by using the spatial autocorrelation method (SPAC). The VS 30 value obtained was 331m/sec, in good agreement with the average values obtained for this area by other authors, using prospecting techniques.

Spatial distribution of the soil carbon pool in a Holm oak dehesa in Spain

Aims Dehesas are agroforestry systems characterized by scattered trees among pastures, crops and/or fallows. A study at a Spanish dehesa has been carried out to estimate the spatial distribution of the soil organic carbon stock and to assess the influence of the tree cover. Methods The soil organic carbon stock was estimated from the five uppermost cm of themineral soil with high spatial resolution at two plots with different grazing intensities. The Universal Kriging technique was used to assess the spatial distribution of the soil organic carbon stocks, using tree coverage within a buffering area as an auxiliary variable. Results A significant positive correlation between tree presence and soil organic carbon stocks up to distances of around 8 m from the trees was found. The tree crown cover within a buffer up to a distance similar to the crown radius around the point absorbed 30 % of the variance in the model for both grazing intensities, but residual variance showed stronger spatial autocorrelation under regular grazing conditions. Conclusions Tree cover increases soil organic carbon stocks, and can be satisfactorily estimated by means of crown parameters. However, other factors are involved in the spatial pattern of the soil organic carbon distribution. Livestock plays an interactive role together with tree presence in soil organic carbon distribution.

Remote sensing of LAI, chlorophyll and leaf nitrogen pools of crop- and grasslands in five European landscapes.

Leaf nitrogen and leaf surface area influence the exchange of gases between terrestrial ecosystems and the atmosphere, and play a significant role in the global cycles of carbon, nitrogen and water. The purpose of this study is to use field-based and satellite remote-sensing-based methods to assess leaf nitrogen pools in five diverse European agricultural landscapes located in Denmark, Scotland (United Kingdom), Poland, the Netherlands and Italy. REGFLEC (REGularized canopy reFLECtance) is an advanced image-based inverse canopy radiative transfer modelling system which has shown proficiency for regional mapping of leaf area index (LAI) and leaf chlorophyll (CHLl) using remote sensing data. In this study, high spatial resolution (10–20 m) remote sensing images acquired from the multispectral sensors aboard the SPOT (Satellite For Observation of Earth) satellites were used to assess the capability of REGFLEC for mapping spatial variations in LAI, CHLland the relation to leaf nitrogen (Nl) data in five diverse European agricultural landscapes. REGFLEC is based on physical laws and includes an automatic model parameterization scheme which makes the tool independent of field data for model calibration. In this study, REGFLEC performance was evaluated using LAI measurements and non-destructive measurements (using a SPAD meter) of leaf-scale CHLl and Nl concentrations in 93 fields representing crop- and grasslands of the five landscapes. Furthermore, empirical relationships between field measurements (LAI, CHLl and Nl and five spectral vegetation indices (the Normalized Difference Vegetation Index, the Simple Ratio, the Enhanced Vegetation Index-2, the Green Normalized Difference Vegetation Index, and the green chlorophyll index) were used to assess field data coherence and to serve as a comparison basis for assessing REGFLEC model performance. The field measurements showed strong vertical CHLl gradient profiles in 26% of fields which affected REGFLEC performance as well as the relationships between spectral vegetation indices (SVIs) and field measurements. When the range of surface types increased, the REGFLEC results were in better agreement with field data than the empirical SVI regression models. Selecting only homogeneous canopies with uniform CHLl distributions as reference data for evaluation, REGFLEC was able to explain 69% of LAI observations (rmse = 0.76), 46% of measured canopy chlorophyll contents (rmse = 719 mg m−2) and 51% of measured canopy nitrogen contents (rmse = 2.7 g m−2). Better results were obtained for individual landscapes, except for Italy, where REGFLEC performed poorly due to a lack of dense vegetation canopies at the time of satellite recording. Presence of vegetation is needed to parameterize the REGFLEC model. Combining REGFLEC- and SVI-based model results to minimize errors for a "snap-shot" assessment of total leaf nitrogen pools in the five landscapes, results varied from 0.6 to 4.0 t km−2. Differences in leaf nitrogen pools between landscapes are attributed to seasonal variations, extents of agricultural area, species variations, and spatial variations in nutrient availability. In order to facilitate a substantial assessment of variations in Nl pools and their relation to landscape based nitrogen and carbon cycling processes, time series of satellite data are needed. The upcoming Sentinel-2 satellite mission will provide new multiple narrowband data opportunities at high spatio-temporal resolution which are expected to further improve remote sensing capabilities for mapping LAI, CHLl and Nl.

Bifurcation diagrams for polymer blends with diffuse interfaces in confined and adaptive geometries

Dynamics of binary mixtures such as polymer blends, and fluids near the critical point, is described by the model-H, which couples momentum transport and diffusion of the components [1]. We present an extended version of the model-H that allows to study the combined effect of phase separation in a polymer blend and surface structuring of the film itself [2]. We apply it to analyze the stability of vertically stratified base states on extended films of polymer blends and show that convective transport leads to new mechanisms of instability as compared to the simpler diffusive case described by the Cahn- Hilliard model [3, 4]. We carry out this analysis for realistic parameters of polymer blends used in experimental setups such as PS/PVME. However, geometrically more complicated states involving lateral structuring, strong deflections of the free surface, oblique diffuse interfaces, checkerboard modes, or droplets of a component above of the other are possible at critical composition solving the Cahn Hilliard equation in the static limit for rectangular domains [5, 6] or with deformable free surfaces [6]. We extend these results for off-critical compositions, since balanced overall composition in experiments are unusual. In particular, we study steady nonlinear solutions of the Cahn-Hilliard equation for bidimensional layers with fixed geometry and deformable free surface. Furthermore we distinguished the cases with and without energetic bias at the free surface. We present bifurcation diagrams for off-critical films of polymer blends with free surfaces, showing their free energy, and the L2-norms of surface deflection and the concentration field, as a function of lateral domain size and mean composition. Simultaneously, we look at spatial dependent profiles of the height and concentration. To treat the problem of films with arbitrary surface deflections our calculations are based on minimizing the free energy functional at given composition and geometric constraints using a variational approach based on the Cahn-Hilliard equation. The problem is solved numerically using the finite element method (FEM).

Impact of introducing longer and heavier vehicles on regional consumer price index and Spanish road freight transport system

This paper applies an integrated modeling approach to the case of Spain; the approach is based on a random utility-based multiregional input-output model and a road transport network model for assessing the effect of introducing longer and heavier vehicles (LHVs) on the regional consumer price index (CPI) and on the transportation system. The approach strongly supports the concept that changes in transport costs derived from the LHV allowance as well as the economic structure of regions have direct and indirect effects on the economy and on the transportation system. Results show that the introduction of LHVs might reduce prices paid by consumers for a representative basket of goods and services in the regions of Spain and would also lead to a reduction in the regional CPI. In addition, the magnitude and extent of changes in the transportation system are estimated by using the commodity-based structure of the approach to identify the effect of traffic changes on traffic flows and on pollutant emissions over the whole network.

Drivers in adopting adaptation strategies to face increased water scarcity in agriculture. A case study in Doñana (Spain) and Makueni (Kenya)

La agricultura es uno de los sectores más afectados por el cambio climático. A pesar de haber demostrado a lo largo de la historia una gran capacidad para adaptarse a nuevas situaciones, hoy en día la agricultura se enfrenta a nuevos retos tales como satisfacer un elevado crecimiento en la demanda de alimentos, desarrollar una agricultura sostenible con el medio ambiente y reducir las emisiones de gases de efecto invernadero. El potencial de adaptación debe ser definido en un contexto que incluya el comportamiento humano, ya que éste juega un papel decisivo en la implementación final de las medidas. Por este motivo, y para desarrollar correctamente políticas que busquen influir en el comportamiento de los agricultores para fomentar la adaptación a estas nuevas condiciones, es necesario entender previamente los procesos de toma de decisiones a nivel individual o de explotación, así como los efectos de los factores que determinan las barreras o motivaciones de la implementación de medidas. Esta Tesis doctoral trata de profundizar en el análisis de factores que influyen en la toma de decisiones de los agricultores para adoptar estrategias de adaptación al cambio climático. Este trabajo revisa la literatura actual y desarrolla un marco metodológico a nivel local y regional. Dos casos de estudio a nivel local (Doñana, España y Makueni, Kenia) han sido llevados a cabo con el fin de explorar el comportamiento de los agricultores hacia la adaptación. Estos casos de estudio representan regiones con notables diferencias en climatología, impactos del cambio climático, barreras para la adaptación y niveles de desarrollo e influencia de las instituciones públicas y privadas en la agricultura. Mientras el caso de estudio de Doñana representa un ejemplo de problemas asociados al uso y escasez del agua donde se espera que se agraven en el futuro, el caso de estudio de Makueni ejemplifica una zona fuertemente amenazada por las predicciones de cambio climático, donde adicionalmente la falta de infraestructura y la tecnología juegan un papel crucial para la implementación de la adaptación. El caso de estudio a nivel regional trata de generalizar en África el comportamiento de los agricultores sobre la implementación de medidas. El marco metodológico que se ha seguido en este trabajo abarca una amplia gama de enfoques y métodos para la recolección y análisis de datos. Los métodos utilizados para la toma de datos incluyen la implementación de encuestas, entrevistas, talleres con grupos de interés, grupos focales de discusión, revisión de estudios previos y bases de datos públicas. Los métodos analíticos incluyen métodos estadísticos, análisis multi‐criterio para la toma de decisiones, modelos de optimización de uso del suelo y un índice compuesto calculado a través de indicadores. Los métodos estadísticos se han utilizado con el fin de evaluar la influencia de los factores socio‐económicos y psicológicos sobre la adopción de medidas de adaptación. Dentro de estos métodos se incluyen regresiones logísticas, análisis de componentes principales y modelos de ecuaciones estructurales. Mientras que el análisis multi‐criterio se ha utilizado con el fin de evaluar las opciones de adaptación de acuerdo a las opiniones de las diferentes partes interesadas, el modelo de optimización ha tenido como fin analizar la combinación óptima de medidas de adaptación. El índice compuesto se ha utilizado para evaluar a nivel regional la implementación de medidas de adaptación en África. En general, los resultados del estudio ponen de relieve la gran importancia de considerar diferentes escalas espaciales a la hora de evaluar la implementación de medidas de adaptación al cambio climático. El comportamiento de los agricultores es diferente entre lugares considerados a una escala local relativamente pequeña, por lo que la generalización de los patrones del comportamiento a escalas regionales o globales resulta relativamente compleja. Los resultados obtenidos han permitido identificar factores determinantes tanto socioeconómicos como psicológicos y calcular su efecto sobre la adopción de medidas de adaptación. Además han proporcionado una mejor comprensión del distinto papel que desempeñan los cinco tipos de capital (natural, físico, financiero, social y humano) en la implementación de estrategias de adaptación. Con este trabajo se proporciona información de gran interés en los procesos de desarrollo de políticas destinadas a mejorar el apoyo de la sociedad a tomar medidas contra el cambio climático. Por último, en el análisis a nivel regional se desarrolla un índice compuesto que muestra la probabilidad de adoptar medidas de adaptación en las regiones de África y se analizan las causas que determinan dicha probabilidad de adopción de medidas. ABSTRACT Agriculture is and will continue to be one of the sectors most affected by climate change. Despite having demonstrated throughout history a great ability to adapt, agriculture today faces new challenges such as meeting growing food demands, developing sustainable agriculture and reducing greenhouse gas emissions. Adaptation policies planned on global, regional or local scales are ultimately implemented in decision‐making processes at the farm or individual level so adaptation potentials have to be set within the context of individual behaviour and regional institutions. Policy instruments can play a formative role in the adoption of such policies by addressing incentives/disincentives that influence farmer’s behaviour. Hence understanding farm‐level decision‐making processes and the influence of determinants of adoption is crucial when designing policies aimed at fostering adoption. This thesis seeks to analyse the factors that influence decision‐making by farmers in relation to the uptake of adaptation options. This work reviews the current knowledge and develops a methodological framework at local and regional level. Whilst the case studies at the local level are conducted with the purpose of exploring farmer’s behaviour towards adaptation the case study at the regional level attempts to up‐scale and generalise theory on adoption of farmlevel adaptation options. The two case studies at the local level (Doñana, Spain and Makueni, Kenya) encompass areas with different; climates, impacts of climate change, adaptation constraints and limits, levels of development, institutional support for agriculture and influence from public and private institutions. Whilst the Doñana Case Study represents an area plagued with water‐usage issues, set to be aggravated further by climate change, Makueni Case study exemplifies an area decidedly threatened by climate change where a lack of infrastructure and technology plays a crucial role in the uptake of adaptation options. The proposed framework is based on a wide range of approaches for collecting and analysing data. The approaches used for data collection include the implementation of surveys, interviews, stakeholder workshops, focus group discussions, a review of previous case studies, and public databases. The analytical methods include statistical approaches, multi criteria analysis for decision‐making, land use optimisation models, and a composite index based on public databases. Statistical approaches are used to assess the influence of socio‐economic and psychological factors on the adoption or support for adaptation measures. The statistical approaches used are logistic regressions, principal component analysis and structural equation modelling. Whilst a multi criteria analysis approach is used to evaluate adaptation options according to the different perspectives of stakeholders, the optimisation model analyses the optimal combination of adaptation options. The composite index is developed to assess adoption of adaptation measures in Africa. Overall, the results of the study highlight the importance of considering various scales when assessing adoption of adaptation measures to climate change. As farmer’s behaviour varies at a local scale there is elevated complexity when generalising behavioural patterns for farmers at regional or global scales. The results identify and estimate the effect of most relevant socioeconomic and psychological factors that influence adoption of adaptation measures to climate change. They also provide a better understanding of the role of the five types of capital (natural, physical, financial, social, and human) on the uptake of farm‐level adaptation options. These assessments of determinants help to explain adoption of climate change measures and provide helpful information in order to design polices aimed at enhancing societal support for adaptation policies. Finally the analysis at the regional level develops a composite index which suggests the likelihood of the regions in Africa to adopt farm‐level adaptation measures and analyses the main causes of this likelihood of adoption.

The Future of the Technologies of Shell and spatial Structures. Bridges

The objective of this lecture is try to predict the future of this important type of spatial structures. In this way the activities of the different IASS Technical Working Groups can be stimulated and coordinated in order to play a more relevant role in this future. To grasp a possible evolution of bridges it is convenient a reflection on the bridge history and on their present situation, particularly in relation to the different existing achievements.

Self assembled and ordered group III nitride nanocolumnar structures for light emitting applications

El objetivo de este trabajo es un estudio profundo del crecimiento selectivo de nanoestructuras de InGaN por epitaxia de haces moleculares asistido por plasma, concentrandose en el potencial de estas estructuras como bloques constituyentes en LEDs de nueva generación. Varias aproximaciones al problema son discutidas; desde estructuras axiales InGaN/GaN, a estructuras core-shell, o nanoestructuras crecidas en sustratos con orientaciones menos convencionales (semi polar y no polar). La primera sección revisa los aspectos básicos del crecimiento auto-ensamblado de nanocolumnas de GaN en sustratos de Si(111). Su morfología y propiedades ópticas son comparadas con las de capas compactas de GaN sobre Si(111). En el caso de las columnas auto-ensambladas de InGaN sobre Si(111), se presentan resultados sobre el efecto de la temperatura de crecimiento en la incorporación de In. Por último, se discute la inclusión de nanodiscos de InGaN en las nanocolumnas de GaN. La segunda sección revisa los mecanismos básicos del crecimiento ordenado de nanoestructuras basadas en GaN, sobre templates de GaN/zafiro. Aumentando la relación III/V localmente, se observan cambios morfológicos; desde islas piramidales, a nanocolumnas de GaN terminadas en planos semipolares, y finalmente, a nanocolumnas finalizadas en planos c polares. Al crecer nanodiscos de InGaN insertados en las nanocolumnas de GaN, las diferentes morfologias mencionadas dan lugar a diferentes propiedades ópticas de los nanodiscos, debido al diferente carácter (semi polar o polar) de los planos cristalinos involucrados. La tercera sección recoge experimentos acerca de los efectos que la temperatura de crecimiento y la razón In/Ga tienen en la morfología y emisión de nanocolumnas ordenadas de InGaN crecidas sobre templates GaN/zafiro. En el rango de temperaturas entre 650 y 750 C, la incorporacion de In puede modificarse bien por la temperatura de crecimiento, o por la razón In/Ga. Controlar estos factores permite la optimización de la longitud de onda de emisión de las nanocolumnas de InGaN. En el caso particular de la generación de luz blanca, se han seguidos dos aproximaciones. En la primera, se obtiene emisión amarilla-blanca a temperatura ambiente de nanoestructuras donde la región de InGaN consiste en un gradiente de composiciones de In, que se ha obtenido a partir de un gradiente de temperatura durante el crecimiento. En la segunda, el apilamiento de segmentos emitiendo en azul, verde y rojo, consiguiendo la integración monolítica de estas estructuras en cada una de las nanocolumnas individuales, da lugar a emisores ordenados con un amplio espectro de emisión. En esta última aproximación, la forma espectral puede controlarse con la longitud (duración del crecimiento) de cada uno de los segmentos de InGaN. Más adelante, se presenta el crecimiento ordenado, por epitaxia de haces moleculares, de arrays de nanocolumnas que son diodos InGaN/GaN cada una de ellas, emitiendo en azul (441 nm), verde (502 nm) y amarillo (568 nm). La zona activa del dispositivo consiste en una sección de InGaN, de composición constante nominalmente y longitud entre 250 y 500 nm, y libre de defectos extendidos en contraste con capas compactas de InGaN de similares composiciones y espesores. Los espectros de electroluminiscencia muestran un muy pequeño desplazamiento al azul al aumentar la corriente inyectada (desplazamiento casi inexistente en el caso del dispositivo amarillo), y emisiones ligeramente más anchas que en el caso del estado del arte en pozos cuánticos de InGaN. A continuación, se presenta y discute el crecimiento ordenado de nanocolumnas de In(Ga)N/GaN en sustratos de Si(111). Nanocolumnas ordenadas emitiendo desde el ultravioleta (3.2 eV) al infrarrojo (0.78 eV) se crecieron sobre sustratos de Si(111) utilizando una capa compacta (“buffer”) de GaN. La morfología y eficiencia de emisión de las nanocolumnas emitiendo en el rango espectral verde pueden ser mejoradas ajustando las relaciones In/Ga y III/N, y una eficiencia cuántica interna del 30% se deriva de las medidas de fotoluminiscencia en nanocolumnas optimizadas. En la siguiente sección de este trabajo se presenta en detalle el mecanismo tras el crecimiento ordenado de nanocolumnas de InGaN/GaN emitiendo en el verde, y sus propiedades ópticas. Nanocolumnas de InGaN/GaN con secciones largas de InGaN (330-830 nm) se crecieron tanto en sustratos GaN/zafiro como GaN/Si(111). Se encuentra que la morfología y la distribución espacial del In dentro de las nanocolumnas dependen de las relaciones III/N e In/Ga locales en el frente de crecimiento de las nanocolumnas. La dispersión en el contenido de In entre diferentes nanocolumnas dentro de la misma muestra es despreciable, como indica las casi identicas formas espectrales de la catodoluminiscencia de una sola nanocolumna y del conjunto de ellas. Para las nanocolumnas de InGaN/GaN crecidas sobre GaN/Si(111) y emitiendo en el rango espectral verde, la eficiencia cuántica interna aumenta hasta el 30% al disminuir la temperatura de crecimiento y aumentar el nitrógeno activo. Este comportamiento se debe probablemente a la formación de estados altamente localizados, como indica la particular evolución de la energía de fotoluminiscencia con la temperatura (ausencia de “s-shape”) en muestras con una alta eficiencia cuántica interna. Por otro lado, no se ha encontrado la misma dependencia entre condiciones de crecimiento y efiencia cuántica interna en las nanoestructuras InGaN/GaN crecidas en GaN/zafiro, donde la máxima eficiencia encontrada ha sido de 3.7%. Como alternativa a las nanoestructuras axiales de InGaN/GaN, la sección 4 presenta resultados sobre el crecimiento y caracterización de estructuras core-shell de InGaN/GaN, re-crecidas sobre arrays de micropilares de GaN fabricados por ataque de un template GaN/zafiro (aproximación top-down). El crecimiento de InGaN/GaN es conformal, con componentes axiales y radiales en el crecimiento, que dan lugar a la estructuras core-shell con claras facetas hexagonales. El crecimiento radial (shell) se ve confirmado por medidas de catodoluminiscencia con resolución espacial efectuadas en un microscopio electrónico de barrido, asi como por medidas de microscopía de transmisión de electrones. Más adelante, el crecimiento de micro-pilares core-shell de InGaN se realizó en pilares GaN (cores) crecidos selectivamente por epitaxia de metal-orgánicos en fase vapor. Con el crecimiento de InGaN se forman estructuras core-shell con emisión alrededor de 3 eV. Medidas de catodoluminiscencia resuelta espacialmente indican un aumento en el contenido de indio del shell en dirección a la parte superior del pilar, que se manifiesta en un desplazamiento de la emisión de 3.2 eV en la parte inferior, a 3.0 eV en la parte superior del shell. Este desplazamiento está relacionado con variaciones locales de la razón III/V en las facetas laterales. Finalmente, se demuestra la fabricación de una estructura pin basada en estos pilares core-shell. Medidas de electroluminiscencia resuelta espacialmente, realizadas en pilares individuales, confirman que la electroluminiscencia proveniente del shell de InGaN (diodo lateral) está alrededor de 3.0 eV, mientras que la emisión desde la parte superior del pilar (diodo axial) está alrededor de 2.3 eV. Para finalizar, se presentan resultados sobre el crecimiento ordenado de GaN, con y sin inserciones de InGaN, en templates semi polares (GaN(11-22)/zafiro) y no polares (GaN(11-20)/zafiro). Tras el crecimiento ordenado, gran parte de los defectos presentes en los templates originales se ven reducidos, manifestándose en una gran mejora de las propiedades ópticas. En el caso de crecimiento selectivo sobre templates con orientación GaN(11-22), no polar, la formación de nanoestructuras con una particular morfología (baja relación entre crecimiento perpedicular frente a paralelo al plano) permite, a partir de la coalescencia de estas nanoestructuras, la fabricación de pseudo-templates no polares de GaN de alta calidad. ABSTRACT The aim of this work is to gain insight into the selective area growth of InGaN nanostructures by plasma assisted molecular beam epitaxy, focusing on their potential as building blocks for next generation LEDs. Several nanocolumn-based approaches such as standard axial InGaN/GaN structures, InGaN/GaN core-shell structures, or InGaN/GaN nanostructures grown on semi- and non-polar substrates are discussed. The first section reviews the basics of the self-assembled growth of GaN nanocolumns on Si(111). Morphology differences and optical properties are compared to those of GaN layer grown directly on Si(111). The effects of the growth temperature on the In incorporation in self-assembled InGaN nanocolumns grown on Si(111) is described. The second section reviews the basic growth mechanisms of selectively grown GaNbased nanostructures on c-plane GaN/sapphire templates. By increasing the local III/V ratio morphological changes from pyramidal islands, to GaN nanocolumns with top semi-polar planes, and further to GaN nanocolumns with top polar c-planes are observed. When growing InGaN nano-disks embedded into the GaN nanocolumns, the different morphologies mentioned lead to different optical properties, due to the semipolar and polar nature of the crystal planes involved. The third section reports on the effect of the growth temperature and In/Ga ratio on the morphology and light emission characteristics of ordered InGaN nanocolumns grown on c-plane GaN/sapphire templates. Within the growth temperature range of 650 to 750oC the In incorporation can be modified either by the growth temperature, or the In/Ga ratio. Control of these factors allows the optimization of the InGaN nanocolumns light emission wavelength. In order to achieve white light emission two approaches are used. First yellow-white light emission can be obtained at room temperature from nanostructures where the InGaN region is composition-graded by using temperature gradients during growth. In a second approach the stacking of red, green and blue emitting segments was used to achieve the monolithic integration of these structures in one single InGaN nanocolumn leading to ordered broad spectrum emitters. With this approach, the spectral shape can be controlled by changing the thickness of the respective InGaN segments. Furthermore the growth of ordered arrays of InGaN/GaN nanocolumnar light emitting diodes by molecular beam epitaxy, emitting in the blue (441 nm), green (502 nm), and yellow (568 nm) spectral range is reported. The device active region, consisting of a nanocolumnar InGaN section of nominally constant composition and 250 to 500 nm length, is free of extended defects, which is in strong contrast to InGaN layers (planar) of similar composition and thickness. Electroluminescence spectra show a very small blue shift with increasing current, (almost negligible in the yellow device) and line widths slightly broader than those of state-of-the-art InGaN quantum wells. Next the selective area growth of In(Ga)N/GaN nanocolumns on Si(111) substrates is discussed. Ordered In(Ga)N/GaN nanocolumns emitting from ultraviolet (3.2 eV) to infrared (0.78 eV) were then grown on top of GaN-buffered Si substrates. The morphology and the emission efficiency of the In(Ga)N/GaN nanocolumns emitting in the green could be substantially improved by tuning the In/Ga and total III/N ratios, where an estimated internal quantum efficiency of 30 % was derived from photoluminescence data. In the next section, this work presents a study on the selective area growth mechanisms of green-emitting InGaN/GaN nanocolumns and their optical properties. InGaN/GaN nanocolumns with long InGaN sections (330-830nm) were grown on GaN/sapphire and GaN-buffered Si(111). The nanocolumn’s morphology and spatial indium distribution is found to depend on the local group (III)/N and In/Ga ratios at the nanocolumn’s top. A negligible spread of the average indium incorporation among different nanostructures is found as indicated by similar shapes of the cathodoluminescence spectra taken from single nanocolumns and ensembles of nanocolumns. For InGaN/GaN nanocolumns grown on GaN-buffered Si(111), all emitting in the green spectral range, the internal quantum efficiency increases up to 30% when decreasing growth temperature and increasing active nitrogen. This behavior is likely due to the formation of highly localized states, as indicated by the absence of a complete s-shape behavior of the PL peak position with temperature (up to room temperature) in samples with high internal quantum efficiency. On the other hand, no dependence of the internal quantum efficiency on the growth conditions is found for InGaN/GaN nanostructures grown on GaN/sapphire, where the maximum achieved efficiency is 3.7%. As alternative to axial InGaN/GaN nanostructures, section 4 reports on the growth and characterization of InGaN/GaN core-shell structures on an ordered array of top-down patterned GaN microrods etched from a GaN/sapphire template. Growth of InGaN/GaN is conformal, with axial and radial growth components leading to core-shell structures with clear hexagonal facets. The radial InGaN growth (shell) is confirmed by spatially resolved cathodoluminescence performed in a scanning electron microscopy as well as in scanning transmission electron microscopy. Furthermore the growth of InGaN core-shell micro pillars using an ordered array of GaN cores grown by metal organic vapor phase epitaxy as a template is demonstrated. Upon InGaN overgrowth core-shell structures with emission at around 3.0 eV are formed. With spatially resolved cathodoluminescence, an increasing In content towards the pillar top is found to be present in the InGaN shell, as indicated by a shift of CL peak position from 3.2 eV at the shell bottom to 3.0 eV at the shell top. This shift is related to variations of the local III/V ratio at the side facets. Further, the successful fabrication of a core-shell pin diode structure is demonstrated. Spatially resolved electroluminescence measurements performed on individual micro LEDs, confirm emission from the InGaN shell (lateral diode) at around 3.0 eV, as well as from the pillar top facet (axial diode) at around 2.3 eV. Finally, this work reports on the selective area growth of GaN, with and without InGaN insertion, on semi-polar (11-22) and non-polar (11-20) templates. Upon SAG the high defect density present in the GaN templates is strongly reduced as indicated by TEM and a dramatic improvement of the optical properties. In case of SAG on non-polar (11-22) templates the formation of nanostructures with a low aspect ratio took place allowing for the fabrication of high-quality, non-polar GaN pseudo-templates by coalescence of the nanostructures.

Accessibility instruments for planning practice: bridging the gap between academic research and decision-making.

One of the core objectives of urban planning practice is to provide spatial equity in terms of opportunities and use of public space and facilities. Accessibility is the element that serves this purpose as a concept linking the reciprocal relationship between transport and land use, thus shaping individual potential mobility to reach the desired destinations. Accessibility concepts are increasingly acknowledged as fundamental to understand the functioning of cities and urban regions. Indeed, by introducing them in planning practice, better solutions can be achieved in terms of spatial equity. The COST Action TU1002 "Accessibility instruments for planning practice" was specifically designed to address the gap between scientific research in measuring and modelling accessibility, and the current use of indicators of accessibility in urban planning practice. This paper shows the full process of introducing an easily understandable measure of accessibility to planning practitioners in Madrid, which is one of the case studies of the above-mentioned COST action. Changes in accessibility after the opening of a new metro line using contour measures were analyzed and then presented to a selection of urban planners and practitioners in Madrid as part of a workshop to evaluate the usefulness of this tool for planning practice. Isochrone maps were confirmed as an effective tool, as their utility can be supplemented by other indicators, and being GIS-based, it can be easily computed (when compared with transport models) and integrated with other datasets.

Low Work-Function Thermionic Emission and Orbital-Motion-Limited Ion Collection at Bare-Tether Cathodic Contact

Una amarra electrodinámica (electrodynamic tether) opera sobre principios electromagnéticos intercambiando momento con la magnetosfera planetaria e interactuando con su ionosfera. Es un subsistema pasivo fiable para desorbitar etapas de cohetes agotadas y satélites al final de su misión, mitigando el crecimiento de la basura espacial. Una amarra sin aislamiento captura electrones del plasma ambiente a lo largo de su segmento polarizado positivamente, el cual puede alcanzar varios kilómetros de longitud, mientras que emite electrones de vuelta al plasma mediante un contactor de plasma activo de baja impedancia en su extremo catódico, tal como un cátodo hueco (hollow cathode). En ausencia de un contactor catódico activo, la corriente que circula por una amarra desnuda en órbita es nula en ambos extremos de la amarra y se dice que ésta está flotando eléctricamente. Para emisión termoiónica despreciable y captura de corriente en condiciones limitadas por movimiento orbital (orbital-motion-limited, OML), el cociente entre las longitudes de los segmentos anódico y catódico es muy pequeño debido a la disparidad de masas entre iones y electrones. Tal modo de operación resulta en una corriente media y fuerza de Lorentz bajas en la amarra, la cual es poco eficiente como dispositivo para desorbitar. El electride C12A7 : e−, que podría presentar una función de trabajo (work function) tan baja como W = 0.6 eV y un comportamiento estable a temperaturas relativamente altas, ha sido propuesto como recubrimiento para amarras desnudas. La emisión termoiónica a lo largo de un segmento así recubierto y bajo el calentamiento de la operación espacial, puede ser más eficiente que la captura iónica. En el modo más simple de fuerza de frenado, podría eliminar la necesidad de un contactor catódico activo y su correspondientes requisitos de alimentación de gas y subsistema de potencia, lo que resultaría en un sistema real de amarra “sin combustible”. Con este recubrimiento de bajo W, cada segmento elemental del segmento catódico de una amarra desnuda de kilómetros de longitud emitiría corriente como si fuese parte de una sonda cilíndrica, caliente y uniformemente polarizada al potencial local de la amarra. La operación es similar a la de una sonda de Langmuir 2D tanto en los segmentos catódico como anódico. Sin embargo, en presencia de emisión, los electrones emitidos resultan en carga espacial (space charge) negativa, la cual reduce el campo eléctrico que los acelera hacia fuera, o incluso puede desacelerarlos y hacerlos volver a la sonda. Se forma una doble vainas (double sheath) estable con electrones emitidos desde la sonda e iones provenientes del plasma ambiente. La densidad de corriente termoiónica, variando a lo largo del segmento catódico, podría seguir dos leyes distintas bajo diferentes condiciones: (i) la ley de corriente limitada por la carga espacial (space-charge-limited, SCL) o (ii) la ley de Richardson-Dushman (RDS). Se presenta un estudio preliminar sobre la corriente SCL frente a una sonda emisora usando la teoría de vainas (sheath) formada por la captura iónica en condiciones OML, y la corriente electrónica SCL entre los electrodos cilíndricos según Langmuir. El modelo, que incluye efectos óhmicos y el efecto de transición de emisión SCL a emisión RDS, proporciona los perfiles de corriente y potencial a lo largo de la longitud completa de la amarra. El análisis muestra que en el modo más simple de fuerza de frenado, bajo condiciones orbitales y de amarras típicas, la emisión termoiónica proporciona un contacto catódico eficiente y resulta en una sección catódica pequeña. En el análisis anterior, tanto la transición de emisión SCL a RD como la propia ley de emisión SCL consiste en un modelo muy simplificado. Por ello, a continuación se ha estudiado con detalle la solución de vaina estacionaria de una sonda con emisión termoiónica polarizada negativamente respecto a un plasma isotrópico, no colisional y sin campo magnético. La existencia de posibles partículas atrapadas ha sido ignorada y el estudio incluye tanto un estudio semi-analítico mediante técnica asintóticas como soluciones numéricas completas del problema. Bajo las tres condiciones (i) alto potencial, (ii) R = Rmax para la validez de la captura iónica OML, y (iii) potencial monotónico, se desarrolla un análisis asintótico auto-consistente para la estructura de plasma compleja que contiene las tres especies de cargas (electrones e iones del plasma, electrones emitidos), y cuatro regiones espaciales distintas, utilizando teorías de movimiento orbital y modelos cinéticos de las especies. Aunque los electrones emitidos presentan carga espacial despreciable muy lejos de la sonda, su efecto no se puede despreciar en el análisis global de la estructura de la vaina y de dos capas finas entre la vaina y la región cuasi-neutra. El análisis proporciona las condiciones paramétricas para que la corriente sea SCL. También muestra que la emisión termoiónica aumenta el radio máximo de la sonda para operar dentro del régimen OML y que la emisión de electrones es mucho más eficiente que la captura iónica para el segmento catódico de la amarra. En el código numérico, los movimientos orbitales de las tres especies son modelados para potenciales tanto monotónico como no-monotónico, y sonda de radio R arbitrario (dentro o más allá del régimen de OML para la captura iónica). Aprovechando la existencia de dos invariante, el sistema de ecuaciones Poisson-Vlasov se escribe como una ecuación integro-diferencial, la cual se discretiza mediante un método de diferencias finitas. El sistema de ecuaciones algebraicas no lineal resultante se ha resuelto de con un método Newton-Raphson paralelizado. Los resultados, comparados satisfactoriamente con el análisis analítico, proporcionan la emisión de corriente y la estructura del plasma y del potencial electrostático. ABSTRACT An electrodynamic tether operates on electromagnetic principles and exchanges momentum through the planetary magnetosphere, by continuously interacting with the ionosphere. It is a reliable passive subsystem to deorbit spent rocket stages and satellites at its end of mission, mitigating the growth of orbital debris. A tether left bare of insulation collects electrons by its own uninsulated and positively biased segment with kilometer range, while electrons are emitted by a low-impedance active device at the cathodic end, such as a hollow cathode, to emit the full electron current. In the absence of an active cathodic device, the current flowing along an orbiting bare tether vanishes at both ends and the tether is said to be electrically floating. For negligible thermionic emission and orbital-motion-limited (OML) collection throughout the entire tether (electron/ion collection at anodic/cathodic segment, respectively), the anodic-to-cathodic length ratio is very small due to ions being much heavier, which results in low average current and Lorentz drag. The electride C12A7 : e−, which might present a possible work function as low as W = 0.6 eV and moderately high temperature stability, has been proposed as coating for floating bare tethers. Thermionic emission along a thus coated cathodic segment, under heating in space operation, can be more efficient than ion collection and, in the simplest drag mode, may eliminate the need for an active cathodic device and its corresponding gas-feed requirements and power subsystem, which would result in a truly “propellant-less” tether system. With this low-W coating, each elemental segment on the cathodic segment of a kilometers-long floating bare-tether would emit current as if it were part of a hot cylindrical probe uniformly polarized at the local tether bias, under 2D probe conditions that are also applied to the anodic-segment analysis. In the presence of emission, emitted electrons result in negative space charge, which decreases the electric field that accelerates them outwards, or even reverses it, decelerating electrons near the emitting probe. A double sheath would be established with electrons being emitted from the probe and ions coming from the ambient plasma. The thermionic current density, varying along the cathodic segment, might follow two distinct laws under different con ditions: i) space-charge-limited (SCL) emission or ii) full Richardson-Dushman (RDS) emission. A preliminary study on the SCL current in front of an emissive probe is presented using the orbital-motion-limited (OML) ion-collection sheath and Langmuir’s SCL electron current between cylindrical electrodes. A detailed calculation of current and bias profiles along the entire tether length is carried out with ohmic effects considered and the transition from SCL to full RDS emission is included. Analysis shows that in the simplest drag mode, under typical orbital and tether conditions, thermionic emission provides efficient cathodic contact and leads to a short cathodic section. In the previous analysis, both the transition between SCL and RDS emission and the current law for SCL condition have used a very simple model. To continue, considering an isotropic, unmagnetized, colissionless plasma and a stationary sheath, the probe-plasma contact is studied in detail for a negatively biased probe with thermionic emission. The possible trapped particles are ignored and this study includes both semianalytical solutions using asymptotic analysis and complete numerical solutions. Under conditions of i) high bias, ii) R = Rmax for ion OML collection validity, and iii) monotonic potential, a self-consistent asymptotic analysis is carried out for the complex plasma structure involving all three charge species (plasma electrons and ions, and emitted electrons) and four distinct spatial regions using orbital motion theories and kinetic modeling of the species. Although emitted electrons present negligible space charge far away from the probe, their effect cannot be neglected in the global analysis for the sheath structure and two thin layers in between the sheath and the quasineutral region. The parametric conditions for the current to be space-chargelimited are obtained. It is found that thermionic emission increases the range of probe radius for OML validity and is greatly more effective than ion collection for cathodic contact of tethers. In the numerical code, the orbital motions of all three species are modeled for both monotonic and non-monotonic potential, and for any probe radius R (within or beyond OML regime for ion collection). Taking advantage of two constants of motion (energy and angular momentum), the Poisson-Vlasov equation is described by an integro differential equation, which is discretized using finite difference method. The non-linear algebraic equations are solved using a parallel implementation of the Newton-Raphson method. The results, which show good agreement with the analytical results, provide the results for thermionic current, the sheath structure, and the electrostatic potential.

Agricultural use of organic wastes as source of nitrogen and phosphorus: risks and opportunities

El nitrógeno (N) y el fósforo (P) son nutrientes esenciales en la producción de cultivos. El desarrollo de los fertilizantes de síntesis durante el siglo XX permitió una intensificación de la agricultura y un aumento de las producciones pero a su vez el gran input de nutrientes ha resultado en algunos casos en sistemas poco eficientes incrementando las pérdidas de estos nutrientes al medio ambiente. En el caso del P, este problema se agrava debido a la escasez de reservas de roca fosfórica necesaria para la fabricación de fertilizantes fosfatados. La utilización de residuos orgánicos en agricultura como fuente de N y P es una buena opción de manejo que permite valorizar la gran cantidad de residuos que se generan. Sin embargo, es importante conocer los procesos que se producen en el suelo tras la aplicación de los mismos, ya que influyen en la disponibilidad de nutrientes que pueden ser utilizados por el cultivo así como en las pérdidas de nutrientes de los agrosistemas que pueden ocasionar problemas de contaminación. Aunque la dinámica del N en el suelo ha sido más estudiada que la del P, los problemas importantes de contaminación por nitratos en zonas vulnerables hacen necesaria la evaluación de aquellas prácticas de manejo que pudieran agravar esta situación, y en el caso de los residuos orgánicos, la evaluación de la respuesta agronómica y medioambiental de la aplicación de materiales con un alto contenido en N (como los residuos procedentes de la industria vinícola y alcoholera). En cuanto al P, debido a la mayor complejidad de su ciclo y de las reacciones que ocurren en el suelo, hay un mayor desconocimiento de los factores que influyen en su dinámica en los sistemas suelo-planta, lo que supone nuevas oportunidades de estudio en la evaluación del uso agrícola de los residuos orgánicos. Teniendo en cuenta los conocimientos previos sobre cada nutriente así como las necesidades específicas en el estudio de los mismos, en esta Tesis se han evaluado: (1) el efecto de la aplicación de residuos procedentes de la industria vinícola y alcoholera en la dinámica del N desde el punto de vista agronómico y medioambiental en una zona vulnerable a la contaminación por nitratos; y (2) los factores que influyen en la disponibilidad de P en el suelo tras la aplicación de residuos orgánicos. Para ello se han llevado a cabo incubaciones de laboratorio así como ensayos de campo que permitieran evaluar la dinámica de estos nutrientes en condiciones reales. Las incubaciones de suelo en condiciones controladas de humedad y temperatura para determinar el N mineralizado se utilizan habitualmente para estimar la disponibilidad de N para el cultivo así como el riesgo medioambiental. Por ello se llevó a cabo una incubación en laboratorio para conocer la velocidad de mineralización de N de un compost obtenido a partir de residuos de la industria vinícola y alcoholera, ampliamente distribuida en Castilla-La Mancha, región con problemas importantes de contaminación de acuíferos por nitratos. Se probaron tres dosis crecientes de compost correspondientes a 230, 460 y 690 kg de N total por hectárea que se mezclaron con un suelo franco arcillo arenoso de la zona. La evolución del N mineral en el suelo a lo largo del tiempo se ajustó a un modelo de regresión no lineal, obteniendo valores bajos de N potencialmente mineralizable y bajas contantes de mineralización, lo que indica que se trata de un material resistente a la mineralización y con una lenta liberación de N en el suelo, mineralizándose tan solo 1.61, 1.33 y 1.21% del N total aplicado con cada dosis creciente de compost (para un periodo de seis meses). Por otra parte, la mineralización de N tras la aplicación de este material también se evaluó en condiciones de campo, mediante la elaboración de un balance de N durante dos ciclos de cultivo (2011 y 2012) de melón bajo riego por goteo, cultivo y manejo agrícola muy característicos de la zona de estudio. Las constantes de mineralización obtenidas en el laboratorio se ajustaron a las temperaturas reales en campo para predecir el N mineralizado en campo durante el ciclo de cultivo del melón, sin embargo este modelo generalmente sobreestimaba el N mineralizado observado en campo, por la influencia de otros factores no tenidos en cuenta para obtener esta predicción, como el N acumulado en el suelo, el efecto de la planta o las fluctuaciones de temperatura y humedad. Tanto el ajuste de los datos del laboratorio al modelo de mineralización como las predicciones del mismo fueron mejores cuando se consideraba el efecto de la mezcla suelo-compost que cuando se aislaba el N mineralizado del compost, mostrando la importancia del efecto del suelo en la mineralización del N procedente de residuos orgánicos. Dado que esta zona de estudio ha sido declarada vulnerable a la contaminación por nitratos y cuenta con diferentes unidades hidrológicas protegidas, en el mismo ensayo de campo con melón bajo riego por goteo se evaluó el riesgo de contaminación por nitratos tras la aplicación de diferentes dosis de compost bajo dos regímenes de riego, riego ajustado a las necesidades del cultivo (90 ó 100% de la evapotranspiración del cultivo (ETc)) o riego excedentario (120% ETc). A lo largo del ciclo de cultivo se estimó semanalmente el drenaje mediante la realización de un balance hídrico, así como se tomaron muestras de la solución de suelo y se determinó su concentración de nitratos. Para evaluar el riesgo de contaminación de las aguas subterráneas asociado con estas prácticas, se utilizaron algunos índices medioambientales para determinar la variación en la calidad del agua potable (Índice de Impacto (II)) y en la concentración de nitratos del acuífero (Índice de Impacto Ambiental (EII)). Para combinar parámetros medioambientales con parámetros de producción, se calculó la eficiencia de manejo. Se observó que la aplicación de compost bajo un régimen de riego ajustado no aumentaba el riesgo de contaminación de las aguas subterráneas incluso con la aplicación de la dosis más alta. Sin embargo, la aplicación de grandes cantidades de compost combinada con un riego excedentario supuso un incremento en el N lixiviado a lo largo del ciclo de cultivo, mientras que no se obtuvieron mayores producciones con respecto al riego ajustado. La aplicación de residuos de la industria vinícola y alcoholera como fuente de P fue evaluada en suelos calizos caracterizados por una alta capacidad de retención de P, lo cual en algunos casos limita la disponibilidad de este nutriente. Para ello se llevó a cabo otro ensayo de incubación con dos suelos de diferente textura, con diferente contenido de carbonato cálcico, hierro y con dos niveles de P disponible; a los que se aplicaron diferentes materiales procedentes de estas industrias (con y sin compostaje previo) aportando diferentes cantidades de P. A lo largo del tiempo se analizó el P disponible del suelo (P Olsen) así como el pH y el carbono orgánico disuelto. Al final de la incubación, con el fin de estudiar los cambios producidos por los diferentes residuos en el estado del P del suelo se llevó a cabo un fraccionamiento del P inorgánico del suelo, el cual se separó en P soluble y débilmente enlazado (NaOH-NaCl-P), P soluble en reductores u ocluido en los óxidos de Fe (CBD-P) y P poco soluble precipitado como Ca-P (HCl-P); y se determinó la capacidad de retención de P así como el grado de saturación de este elemento en el suelo. En este ensayo se observó que, dada la naturaleza caliza de los suelos, la influencia de la cantidad de P aplicado con los residuos en el P disponible sólo se producía al comienzo del periodo de incubación, mientras que al final del ensayo el incremento en el P disponible del suelo se igualaba independientemente del P aplicado con cada residuo, aumentando el P retenido en la fracción menos soluble con el aumento del P aplicado. Por el contrario, la aplicación de materiales orgánicos menos estabilizados y con un menor contenido en P, produjo un aumento en las formas de P más lábiles debido a una disolución del P retenido en la fracción menos lábil, lo cual demostró la influencia de la materia orgánica en los procesos que controlan el P disponible en el suelo. La aplicación de residuos aumentó el grado de saturación de P de los suelos, sin embargo los valores obtenidos no superaron los límites establecidos que indican un riesgo de contaminación de las aguas. La influencia de la aplicación de residuos orgánicos en las formas de P inorgánico y orgánico del suelo se estudió además en un suelo ácido de textura areno francosa tras la aplicación en campo a largo plazo de estiércol vacuno y de compost obtenido a partir de biorresiduos, así como la aplicación combinada de compost y un fertilizante mineral (superfosfato tripe), en una rotación de cultivos. En muestras de suelo recogidas 14 años después del establecimiento del experimento en campo, se determinó el P soluble y disponible, la capacidad de adsorción de P, el grado de saturación de P así como diferentes actividades enzimáticas (actividad deshidrogenasa, fosfatasa ácida y fosfatasa alcalina). Las diferentes formas de P orgánico en el suelo se estudiaron mediante una técnica de adición de enzimas con diferentes substratos específicos a extractos de suelo de NaOH-EDTA, midiendo el P hidrolizado durante un periodo de incubación por colorimetría. Las enzimas utilizadas fueron la fosfatasa ácida, la nucleasa y la fitasa las cuales permitieron identificar monoésteres hidrolizables (monoester-like P), diésteres (DNA-like P) e inositol hexaquifosfato (Ins6P-like P). La aplicación a largo plazo de residuos orgánicos aumentó el P disponible del suelo proporcionalmente al P aplicado con cada tipo de fertilización, suponiendo un mayor riesgo de pérdidas de P dado el alto grado de saturación de este suelo. La aplicación de residuos orgánicos aumentó el P orgánico del suelo resistente a la hidrólisis enzimática, sin embargo no influyó en las diferentes formas de P hidrolizable por las enzimas en comparación con las observadas en el suelo sin enmendar. Además, las diferentes formas de P orgánico aplicadas con los residuos orgánicos no se correspondieron con las analizadas en el suelo lo cual demostró que éstas son el resultado de diferentes procesos en el suelo mediados por las plantas, los microorganismos u otros procesos abióticos. En este estudio se encontró una correlación entre el Ins6P-like P y la actividad microbiana (actividad deshidrogenasa) del suelo, lo cual refuerza esta afirmación. Por último, la aplicación de residuos orgánicos como fuente de N y P en la agricultura se evaluó agronómicamente en un escenario real. Se estableció un experimento de campo para evaluar el compost procedente de residuos de bodegas y alcoholeras en el mismo cultivo de melón utilizado en el estudio de la mineralización y lixiviación de N. En este experimento se estudió la aplicación de tres dosis de compost: 1, 2 y 3 kg de compost por metro lineal de plantación correspondientes a 7, 13 y 20 t de compost por hectárea respectivamente; y se estudió el efecto sobre el crecimiento de las plantas, la acumulación de N y P en la planta, así como la producción y calidad del cultivo. La aplicación del compost produjo un ligero incremento en la biomasa vegetal acompañado por una mejora significativa de la producción con respecto a las parcelas no enmendadas, obteniéndose la máxima producción con la aplicación de 2 kg de compost por metro lineal. Aunque los efectos potenciales del N y P fueron parcialmente enmascarados por otras entradas de estos nutrientes en el sistema (alta concentración de nitratos en el agua de riego y ácido fosfórico suministrado por fertirrigación), se observó una mayor acumulación de P uno de los años de estudio que resultó en un aumento en el número de frutos en las parcelas enmendadas. Además, la mayor acumulación de N y P disponible en el suelo al final del ciclo de cultivo indicó el potencial uso de estos materiales como fuente de estos nutrientes. ABSTRACT Nitrogen (N) and phosphorus (P) are essential nutrients in crop production. The development of synthetic fertilizers during the 20th century allowed an intensification of the agriculture increasing crop yields but in turn the great input of nutrients has resulted in some cases in inefficient systems with higher losses to the environment. Regarding P, the scarcity of phosphate rock reserves necessary for the production of phosphate fertilizers aggravates this problem. The use of organic wastes in agriculture as a source of N and P is a good option of management that allows to value the large amount of wastes generated. However, it is important to understand the processes occurring in the soil after application of these materials, as they affect the availability of nutrients that can be used by the crop and the nutrient losses from agricultural systems that can cause problems of contamination. Although soil N dynamic has been more studied than P, the important concern of nitrate pollution in Nitrate Vulnerable Zones requires the evaluation of those management practices that could aggravate this situation, and in the case of organic wastes, the evaluation of the agronomic and environmental response after application of materials with a high N content (such as wastes from winery and distillery industries). On the other hand, due to the complexity of soil P cycle and the reactions that occur in soil, there is less knowledge about the factors that can influence its dynamics in the soil-plant system, which means new opportunities of study regarding the evaluation of the agricultural use of organic wastes. Taking into account the previous knowledge of each nutrient and the specific needs of study, in this Thesis we have evaluated: (1) the effect of the application of wastes from the winery and distillery industries on N dynamics from the agronomic and environmental viewpoint in a vulnerable zone; and (2) the factors that influence P availability in soils after the application of organic wastes. With this purposes, incubations were carried out in laboratory conditions as well as field trials that allow to assess the dynamic of these nutrients in real conditions. Soil incubations under controlled moisture and temperature conditions to determine N mineralization are commonly used to estimate N availability for crops together with the environmental risk. Therefore, a laboratory incubation was conducted in order to determine the N mineralization rate of a compost made from wastes generated in the winery and distillery industries, widely distributed in Castilla-La Mancha, a region with significant problems of aquifers contamination by nitrates. Three increasing doses of compost corresponding to 230, 460 and 690 kg of total N per hectare were mixed with a sandy clay loam soil collected in this area. The evolution of mineral N in soil over time was adjusted to a nonlinear regression model, obtaining low values of potentially mineralizable N and low constants of mineralization, indicating that it is a material resistant to mineralization with a slow release of N, with only 1.61, 1.33 and 1.21% of total N applied being mineralized with each increasing dose of compost (for a period of six months). Furthermore, N mineralization after the application of this material was also evaluated in field conditions by carrying out a N balance during two growing seasons (2011 and 2012) of a melon crop under drip irrigation, a crop and management very characteristic of the area of study. The mineralization constants obtained in the laboratory were adjusted to the actual temperatures observed in the field to predict N mineralized during each growing season, however, this model generally overestimated the N mineralization observed in the field, because of the influence of other factors not taken into account for this prediction, as N accumulated in soil, the plant effect or the fluctuations of temperature and moisture. The fitting of the laboratory data to the model as well as the predictions of N mineralized in the field were better when considering N mineralized from the soil-compost mixture rather than when N mineralized from compost was isolated, underlining the important role of the soil on N mineralization from organic wastes. Since the area of study was declared vulnerable to nitrate pollution and is situated between different protected hydrological units, the risk of nitrate pollution after application of different doses compost was evaluated in the same field trial with melon under two irrigation regimes, irrigation adjusted to the crop needs (90 or 100% of the crop evapotranspiration (ETc)) or excedentary irrigation (120% ETc). Drainage was estimated weekly throughout the growing season by conducting a water balance, samples of the soil solution were taken and the concentration of nitrates was determined. To assess the risk of groundwater contamination associated with these practices, some environmental indices were used to determine the variation in the quality of drinking water (Impact Index (II)) and the nitrates concentration in the groundwater (Environmental Impact Index (EII)). To combine environmental parameters together with yield parameters, the Management Efficiency was calculated. It was observed that the application of compost under irrigation adjusted to the plant needs did not represent a higher risk of groundwater contamination even with the application of the highest doses. However, the application of large amounts of compost combined with an irrigation surplus represented an increase of N leaching during the growing season compared with the unamended plots, while no additional yield with respect to the adjusted irrigation strategy is obtained. The application of wastes derived from the winery and distillery industry as source of P was evaluated in calcareous soils characterized by a high P retention capacity, which in some cases limits the availability of this nutrient. Another incubation experiment was carried out using two soils with different texture, different calcium carbonate and iron contents and two levels of available P; to which different materials from these industries (with and without composting) were applied providing different amounts of P. Soil available P (Olsen P), pH and dissolved organic carbon were analyzed along time. At the end of the incubation, in order to study the changes in soil P status caused by the different residues, a fractionation of soil inorganic P was carried out, which was separated into soluble and weakly bound P (NaOH-NaCl- P), reductant soluble P or occluded in Fe oxides (CBD-P) and P precipitated as poorly soluble Ca-P (HCl-P); and the P retention capacity and degree of P saturation were determined as well. Given the calcareous nature of the soils, the influence of the amount of P applied with the organic wastes in soil available P only occurred at the beginning of the incubation period, while at the end of the trial the increase in soil available P equalled independently of the amount of P applied with each residue, increasing the P retained in the least soluble fraction when increasing P applied. Conversely, the application of less stabilized materials with a lower content of P resulted in an increase in the most labile P forms due to dissolution of P retained in the less labile fraction, demonstrating the influence of organic matter addition on soil P processes that control P availability in soil. As expected, the application of organic wastes increased the degree of P saturation in the soils, however the values obtained did not exceed the limits considered to pose a risk of water pollution. The influence of the application of organic wastes on inorganic and organic soil P forms was also studied in an acid loamy sand soil after long-term field application of cattle manure and biowaste compost and the combined application of compost and mineral fertilizer (triple superphosphate) in a crop rotation. Soil samples were collected 14 years after the establishment of the field experiment, and analyzed for soluble and available P, P sorption capacity, degree of P saturation and enzymatic activities (dehydrogenase, acid phosphatase and alkaline phosphatase). The different forms of organic P in soil were determined by using an enzyme addition technique, based on adding enzymes with different substrate specificities to NaOH-EDTA soil extracts, measuring the hydrolyzed P colorimetrically after an incubation period. The enzymes used were acid phosphatase, nuclease and phytase which allowed to identify hydrolyzable monoesters (monoester-like P) diesters (DNA-like P) and inositol hexakisphosphate (Ins6P-like P). The long-term application of organic wastes increased soil available P proportionally to the P applied with each type of fertilizer, assuming a higher risk of P losses given the high degree of P saturation of this soil. The application of organic wastes increased soil organic P resistant to enzymatic hydrolysis, but no influence was observed regarding the different forms of enzyme hydrolyzable organic P compared to those observed in the non-amended soil. Furthermore, the different forms of organic P applied with the organic wastes did not correspond to those analyzed in the soil which showed that these forms in soil are a result of multifaceted P turnover processes in soil affected by plants, microorganisms and abiotic factors. In this study, a correlation between Ins6P-like P and the microbial activity (dehydrogenase activity) of soil was found, which reinforces this claim. Finally, the application of organic wastes as a source of N and P in agriculture was evaluated agronomically in a real field scenario. A field experiment was established to evaluate the application of compost made from wine-distillery wastes in the same melon crop used in the experiments of N mineralization and leaching. In this experiment the application of three doses of compost were studied: 1 , 2 and 3 kg of compost per linear meter of plantation corresponding to 7, 13 and 20 tonnes of compost per hectare respectively; and the effect on plant growth, N and P accumulation in the plant as well as crop yield and quality was studied. The application of compost produced a slight increase in plant biomass accompanied by a significant improvement in crop yield with respect to the unamended plots, obtaining the maximum yield with the application of 2 kg of compost per linear meter. Although the potential effects of N and P were partially masked by other inputs of these nutrients in the system (high concentration of nitrates in the irrigation water and phosphoric acid supplied by fertigation), an effect of P was observed the first year of study resulting in a greater plant P accumulation and in an increase in the number of fruits in the amended plots. In addition, the higher accumulation of available N and P in the topsoil at the end of the growing season indicated the potential use of this material as source of these nutrients.

Contribute to the Study of Vertical Distribution of Conventional No-Till Seeders and Spatial Variability of Seed Depth Placement of Maize in Alentejo, Portugal

Entre os vários fatores que contribuem para a produção de uma cultura de milho, a distribuição vertical dos semeadores avaliada através da localização da semente em profundidade é um fator-chave, especialmente na técnica de sementeira direta. Simultaneamente, dada a complexidade dos ecossistemas naturais e agrícolas em sistemas de agricultura de conservação, a gestão diferenciada e localizada das parcelas assume um importante papel na análise e gestão da variabilidade das propriedades do solo e estabelecimento das culturas, nomeadamente utilizando informação geo referenciada e tecnologia expedita. Assim, o principal objetivo desta Tese foi a avaliação em culturas de milho da variabilidade espacial da localização de semente em profundidade e estabelecimento da cultura em sementeira direta usando sistemas convencionais de controlo de profundidade, tendo-se comparado com diferentes sistemas de mobilização e recorrendo a tecnologias de agricultura de precisão. Os ensaios decorreram na região Mediterrânea do Alentejo, em propriedades agrícolas no decorrer das campanhas de 2010, 2011, 2012 e 2015 em 6 diferentes campos experimentais. O trabalho experimental consistiu em ensaios com avaliações in loco do solo e cultura, consumo de combustível das operações e deteção remota. Os resultados obtidos indicam que não só o sistema de mobilização afetou a localização da semente em profundidade, como em sementeira direta a profundidade de sementeira foi afetada pelo teor de humidade do solo, resistência do solo à profundidade e velocidade da operação de sementeira. Adicionalmente observaram-se condições heterogéneas de emergência e estabelecimento da cultura afetadas por condições físicas de compactação do solo. Comparando os diferentes sistemas de mobilização, obteve-se uma significativa redução de combustível para a técnica de sementeira direta, apesar de se terem observado diferenças estatísticas significativas considerando diferentes calibrações de profundidade de sementeira Do trabalho realizado nesta Tese ressalva-se a importância que as tecnologias de agricultura de precisão podem ter no acompanhamento e avaliação de culturas em sementeira direta, bem como a necessidade de melhores procedimentos no controlo de profundidade dos semeadores pelo respetivos operadores ou ao invés, a adoção de semeadores com mecanismos ativos de controlo de profundidade. ABSTRACT Among the various factors that contribute towards producing a successful maize crop, seeders vertical distribution evaluated through seed depth placement is a key determinant, especially under a no-tillage technique. At the same time in conservation agriculture systems due to the complexity of natural and agricultural ecosystems site specific management became an important approach to understand and manage the variability of soil properties and crop establishment, especially when using geo spatial information and affording readily technology Thus, the main objective of this Thesis was to evaluate the spatial variability of seed depth placement and crop establishment in maize crops under no-tillage conditions compared to different tillage systems, using conventional seed depth control no till seeders and precision farming technologies. Trials were carried out in the Mediterranean region of Alentejo, in private farms along the sowing operations season over the years 2010, 2011, 2012 and 2015 in 6 different experimental fields. Experimental work covered field tests with in loco soil and crop evaluations, fuel operation evaluations and aerial sensing. The results obtained indicate that not only tillage system affected seed depth placement but under no till conditions seed depth was affected by soil moisture content, soil resistance to penetration and seeders forward speed. In addition uneven crop seedling and establishment depended on seed depth placement and could be affected by physical problems of compaction layers. Significant reduction in fuel consumption was observed for no till operations although significant differences observed according to different setting calibrations of seed depth control. According to the results, precision agriculture is an important tool to evaluate crops under no till conditions and seed depth mechanisms should be more accurate by the operators or is determinant the adoption of new active depth control technology to improve seeders performance.

Geographical structuring in the mtDNA of Italians.

Geographical patterns of mtDNA variation were studied in 12 Italian samples (1072 individuals) by two different spatial autocorrelation methods. Separate analyses of the frequencies of 12 restriction morphs show North-South clines, differences between Sardinia and the mainland populations, and the effects of isolation by distance. A recently developed autocorrelation statistic summarizing molecular similarity at all sites (AIDA; autocorrelation index for DNA analysis) confirms the presence of a clinical pattern; differences between random pairs of haplotypes tend to increase with their geographical distance. The partition of gene diversity, however, reveals that most variability occurs within populations, whereas differences between populations are minor (GST = 0.057). When the data from the 12 samples are pooled, two descriptors of genetic variability (number of polymorphic sites and average sequence difference between pairs of individuals) do not behave as expected under neutrality. The presence of clinal patterns, Tajima's tests, and a simulation experiment agree in suggesting that population sizes increased rapidly in Italy and Sicily but not necessarily so in Sardinia. The distribution of pairwise sequence differences in the Italian peninsula (excluding Sardinia) permits a tentative location of the demographic increase between 8000 and 20,500 years ago. These dates are consistent with archaeological estimates of two distinct expansion processes, occurring, respectively, in the Neolithic and after the last glacial maximum in the Paleolithic. Conversely, there is no genetic evidence that such processes have had a major impact on the Sardinian population.

Genetics and the origin of European languages.

A new set of European genetic data has been analyzed to dissect independent patterns of geographic variation. The most important cause of European genetic variation has been confirmed to correspond to the migration of Neolithic farmers from the area of origin of agriculture in the Middle East. The next most important component of genetic variation is apparently associated with a north-south gradient possibly due to adaptation to cold climates but also to the differentiation of the Uralic and the Indo-European language-speaking people; however, the relevant correlations are not significantly different from zero after elimination of the spatial autocorrelation. The third component is highly correlated with the infiltration of the Yamna ("Kurgan") people, nomadic pastoralists who domesticated the horse and who have been claimed to have spread Indo-European languages to Europe; this association, which is statistically significant even when taking spatial autocorrelations into account, does not completely exclude the hypothesis of Indo-European as the language of Neolithic farmers. It is possible that both expansions were responsible for the spread of different subfamilies of Indo-European languages, but our genetic data cannot resolve their relative importance.