Causes of legume-rotation effects in increasing cereal yields across the Sudanian, Sahelian and Guinean zone of West Africa

On-farm experiments and pot trials were conducted on eight West African soils to explore the mechanisms governing the often reported legume rotation-induced cereal growth increases in this region. Crops comprised pearl millet (Pennisetum glaucum L.), sorghum (Sorghum bicolor Moench), maize (Zea mays L.), cowpea (Vigna unguiculata Walp.) and groundnut (Arachis hypogaea L.). In groundnut trials the observed 26 to 85% increases in total dry matter (TDM) of rotation cereals (RC) compared with continuous cereals (CC) in the 4th year appeared to be triggered by site- and crop-specific early season differences in nematode infestation (up to 6-fold lower in RC than in CC), enhanced Nmin and a 7% increase in mycorrhizal (AM) infection. In cowpea trials yield effects on millet and differences in nematode numbers, Nmin and AM were much smaller. Rhizosphere studies indicated effects on pH and acid phosphatase activity as secondary causes for the observed growth differences between RC and CC. In the study region legume-rotation effects on cereals seemed to depend on the capability of the legume to suppress nematodes and to enhance early N and P availability for the subsequent cereal.

Causes of legume rotation induced yield increases in cereals grown on West African soils

This study was conducted to investigate soil biological and chemical factors that give rise to cereal yield enhancing effects of legume rotations on sandy, nutrient poor West African soils. The aim was not only to gain more information on the role of legume residues and microorganisms in the soil nutrient cycle. But the study aimed at evaluating if differences in substrate qualities (e.g. root residues) cause changes in the microbial community structure due to specific and highly complex microbe-root-soil interactions. Site and system specific reactions of microorganisms towards rewetting, simulating the onset of rainy season, were observed. Higher respiration rates, higher amounts of microbial biomass carbon (Cmic) and nitrogen (Nmic) as well as higher ergosterol, muramic acid, glucosamine and adenylate concentrations were measured in CL soils of Koukombo and in both soils from Fada. The immediate increase in ATP concentrations after rewetting was likely caused by rehydration of microbial cells where N was not immobilized and, thus, available for plants facilitating their rapid development. Legume root residues led only to slightly better plant performances compared to the control, while the application of cereal roots reduced seedling growth. In contrast to sorghum seedlings, the microbial community did not react to the mineral treatment. Thus the energy supply in form of organic amendments increased microbial indices compared to mineral P application and the control. The results of basal respiration rates, Cmic and Corg levels indicate that the microbial community in the soil from Koukombo is less efficient in substrate use compared to microorganisms in the soil from Fada. However, the continuous carbon input by legume root residues might have contributed to these differences in soil fertility. With the 33P isotopic exchange method a low buffering capacity was detected in both soils irrespective of treatments. Calculated E values (E1min to E1min-1d and E1d-3m) indicated a slowly release of P due to root turnover while applied mineral P is taken up by plants or fixed to the soil. Due to the fact that sorghum growth reacted mainly to the application of mineral P and the microorganisms solely to the organic inputs, the combination of both amendments seems to be the best approach to a sustainable increase of crop production on many nutrient-poor, sandy West African soils. In a pot experiment, were CC and CL soils from Fada and Koukombo were adjusted to the same level of P and N concentrations, crop growth was significantly higher on CL soils, compared to the respective treatments on CC soils. Mycorrhizal infection of roots was increased and the number of nematodes, predominantly free living nematodes, was almost halfed on rotation soils. In conclusion, increased nutrient availability (especially P and N) through the introduction of legumes is not the only reason for the observed yield increasing effects. Soil biological factors seem to also play an important role. In a root chamber experiment the pH gradient along the root-soil-interface was measured at three times using an antimony microelectrode. For Fada soils, pH values were higher on CL than CC soils while the opposite was true for the Koukombo soils. Site-specific differences between Fada and Koukombo soils in N content and microbial community structures might have created varying crop performances leading to the contrasting pH findings. However, the mechanisms involved in this highly complex microbe-root-soil interaction remain unclear.

Symptoms and causes of poverty in a rural Vietnamese commune: Does ethnicity matter?

This study uses data from a sample survey of 200 households drawn from a mountainous commune in Vietnam’s North Central Coast region to measure and explain relative poverty. Principal components analysis is used to construct a multidimensional index of poverty outcomes from variables measuring household income and the value of domestic assets. This index of poverty is then regressed on likely causes of poverty including different forms of resource endowment and social exclusion defined by gender and ethnicity. The ordinary least squares estimates indicate that poverty is indeed influenced by ethnicity, partly through its interaction with social capital. However, poverty is most strongly affected by differences in human and social capital. Differences in the amount of livestock and high quality farmland owned also matter. Thai households are poorer than their Kinh counterparts even when endowed with the same levels of human, social, physical and natural capital considered in the study. This empirical result provides a rationale for further research on the causal relationship between ethnicity and poverty outcomes.

Causes and Effects of Chaos

Most of the recent literature on chaos and nonlinear dynamics is written either for popular science magazine readers or for advanced mathematicians. This paper gives a broad introduction to this interesting and rapidly growing field at a level that is between the two. The graphical and analytical tools used in the literature are explained and demonstrated, the rudiments of the current theory are outlined and that theory is discussed in the context of several examples: an electronic circuit, a chemical reaction and a system of satellites in the solar system.

Use of multilevel logistic regression to identify the causes of differential item functioning

Resumen tomado de la publicaci??n

Dissolution of Dynamic Electronic Institutions, a first approach: Relevant factors and causes

In the context of the digital business ecosystems, small organizations cooperate between them in order to achieve common goals or offer new services for expanding their markets. There are different approaches for these cooperation models such as virtual enterprises, virtual organizations or dynamic electronic institutions which in their lifecycle have in common a dissolution phase. However this phase has not been studied deeply in the current literature and it lacks formalization. In this paper a first approach for achieving and managing the dissolution phase is proposed, as well as a CBR process in order to support it in a multi-agent system

Anàlisi del perfil i de les causes de l'abandonament a l'educació superior. 'Análisis del perfil y de las causas del abandono en la educación superior'.

Resumen tomado del autor

The causes of illegal drug industry growth in the Andes, Anti-Drug Policies and their effectiveness

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Involvement in environmental causes, does the joint effect between subjective income and the performance of the country matter?

Previous research has shown that richer people are more likely to engage in an environmentalcause. We extend it by considering the joint effect between subjective income and a set of macroeconomicvariables. For doing so, we employ the fifth wave of the World Values Survey (WVS).This study provides clear evidence that even when both factors matter, people´s attitudes cruciallydepend on the interaction effect. Hence, those measures that affect the characteristics of thecountry would also change the disposition to be involved.

La síntesis de Newton. La relació i la integració d'informació i conceptes. Interès per esbrinar els fenòmens i les seves causes. 'La síntesis de Newton, la relación y la integración de información y conceptos. Interés por descubrir los fenómenos y sus causas'.

Crédito variable dirigido a educación secundaria obligatoria 12-16 años, en el cual se desarrollan los siguientes temas del área de ciencias experimentales: 1. movimientos rectilineos, 2. fuerzas y movimiento, 3. interacción gravitatoria y la gravitación universal, 4. efectos de la interacción gravitatoria en el equilibrio de los cuerpos y 5. los objetos celestes y su disposición en estructuras, trantando que el alumno conozca sus conceptos fundamentales. Se sugieren 30 actividades de aprendizaje.

La pressió. L'observació i l'anàlisi d'equilibris i diferències. Interès per relacionar causes i efectes a la vida diària. 'La presión. La observación y el análisis de equilibrios y diferencias. Interés por relacionar causas y efectos en la vida diaria'.

Crédito para educación secundaria obligatoria 12-16 años para el área de ciencias experimentales en el que se pretende que el alumno se familiarice con los principios básicos de la física y los relacione con los fenómenos cotidianos. Se usa una metodología activa-experimental y se desarrollan los siguientes temas: Transferencia de energía y cambios. Energía y máquinas. Energía y calor. y Energía y ondas. Se sugieren 28 actividades de aprendizaje y 6 actividades de evaluación. Se ofrecen orientaciones didácticas para el profesor.

Els problemes de comportament en el context escolar : causes i models d'intervenció en l'educació secundària obligatòria : estudi psicopedagògic. 'Los problemas de comportamiento en el contexto escolar : causas y modelos de intervención en la educación secundaria obligatoria : estudio pedagógico'.

Resumen de la autora en catalán

Actituds de professionals relacionats amb la delinquència envers les causes, la prevenció i el tractament de la mateixa. 'Actitudes de profesionales relacionados con la delincuencia respecto a las causas, la prevención y el tratamiento de la misma'.

Conocer y describir las actitudes que manifiestan ciertos colectivos de profesionales que se relacionan más o menos directamente con los delincuentes, en relación a las causas, prevención y tratamiento de la delincuencia. Estudio 1: 382 estudiantes de Psicología y Medicina de la UAB. Estudio 2: 535 sujetos pertenecientes a la Dirección General de Servicios Penitenciarios y Rehabilitacion de la Generalitat, Dirección General de Protección y Tutela de Menores, Servicios para la infancia y adolescencia del ICASS, Servicios Sociales del Ayuntamiento de Barcelona, cuerpos de policía catalana, periodistas de sucesos y profesores universitarios. El método de elección ha sido el opinativo o estratégico, mayoritariamente. Investigación empírica. Plantea el marco teórico sobre la delincuencia y realiza dos estudios. En el primero elabora un instrumento de medida de actitudes que administra a la muestra 1, así como una batería de tests. Realiza un análisis factorial de los datos a partir del cual selecciona los ítems que forman la escala ad hoc EAD (Escala de Actitudes hacia la Delincuencia), compuesta por tres subescalas: causas, prevención y tratamiento. Calcula la fiabilidad y validez. El segundo estudio consiste en la administración de la EAD a la segunda muestra. Plantea unas hipótesis y realiza un análisis estadístico de los datos por ordenador, comparando las puntuaciones obtenidas en los diferentes grupos de profesionales en las tres subescalas. EAD, Escala de conservadurismo social de Wilson de actitudes sociales, Escala de actitudes hacia los presos de Malvinet. ANOVA, Chi-cuadrado, análisis de componentes principales, índices de fiabilidad y validez, representaciones gráficas y SPSS/PC+. Todos los colectivos de profesionales manifiestan actitudes globales de tipo ambiental hacia las causas de la delincuencia y de intervención social y asistencia socioeducativa no punitivas, con alternativas a la prisión clásica hacia la prevención y el tratamiento de la conducta delictiva, si bien los funcionarios y los policías son los grupos que manifiestan esta actitud con menor grado debido a su rol profesional. A partir de las actitudes favorables mostradas por los colectivos evaluados, está previsto estudiar actitudes hacia aspectos concretos de la delincuencia mediante investigaciones de tipo confirmatorio y teniendo en cuenta las variables demográficas de cada colectivo.

Causes of the wage effects of job-worker mismatches : an international comparison. 'Causas de los efectos salariales del desajuste entre trabajador y empleo : una comparación internacional'.

Se analiza, en el ámbito del mercado de trabajo, la adecuación existente entre la cualificación de los trabajadores y aquella que es requerida en sus puestos de trabajo. Habitualmente, la literatura especializada aproxima la educación formal a la cualificación, pese a que la educación formal no proporciona todas las competencias de capital humano que poseen los trabajadores y que requieren sus empleos. Por ello, siendo conscientes de la limitación que supone la utilización de la educación formal como medida de la cualificación, se analiza de forma diferenciada dos fenómenos que tienen lugar en el mercado de trabajo: el ajuste educativo y el ajuste en cualificación.

Snow : causes and effects.

En esta serie los jóvenes lectores se acercan a los diferentes tipos de clima que experimentamos en la Tierra. Además de tratar el tema de un fenómeno meteorológico en particular, se incluye información sobre el pronostico del tiempo y vemos, además, las formas en que las personas, los animales y las plantas modifican su comportamiento de acuerdo a determinadas condiciones meteorológicas.