292 research outputs found
Monograph waterlogging and its effect on the physiology growth and yield of wheat in mediterranean areas managed under no tillage
Get PDFMemoria para optar al título profesional de Ingeniero AgrónomoEn los últimos años ha aumentado el uso de la cero labranza, debido a que presenta una serie de beneficios comparada con la labranza convencional, tales como reducir el uso de combustibles fósiles, disminuir la erosión y mejorar el drenaje de los suelos. Sin embargo, se ha observado que cultivos en suelos de texturas medias a finas, manejados bajo este sistema, disminuyen sus rendimientos en años lluviosos cuando se compara con la labranza convencional. El objetivo de este trabajo fue recopilar información necesaria para analizar si la disminución del rendimiento de trigo en ambientes mediterráneos está relacionada a un evento de anegamiento, observando sus principales causas y efectos sobre el cultivo de trigo. Para esto se efectuó una recopilación y análisis de diversas revistas científicas y libros especializados vinculados a ciencias del suelo, fisiología vegetal y agronomía. Los antecedentes señalaron que el uso de la cero labranza en suelos de texturas medias a finas está asociado a un problema de compactación superficial, factor que afecta la hidrología del suelo, sugiriendo la posibilidad de eventos de anegamiento durante el periodo de lluvias. Junto a esto, dicho estrés altera la difusión del oxígeno en el suelo, provocando una disminución en su concentración y el aumento de compuestos potencialmente tóxicos para el cultivo. A nivel de planta, el anegamiento causa una crisis energética, con una disminución en el intercambio gaseoso y en la absorción de agua y nutrientes, que se traduce
Alice Miel and Democratic Schooling: An Early Curriculum Leader\u27s Ideas on Social Learning and Social Studies
Get PDFAlice Miel, a nationally prominent curriculum development scholar-practitioner at Teachers College of Columbia University for some three decades (1942-1971), frequently has been overlooked in research on the nature and evolution of the curriculum field and the progressive education movement. Furthermore, her contributions have been overlooked even as attention to women in the curriculum field and in educational history has risen. This study addresses this oversight.
Miel became a leading figure in the curriculum field largely on the basis of her progressive-era advocacy and practice of democratic social learning as a primary goal of schooling in the United States. This study explores major influences on her ideas, her understandings of democratic concepts and principles, and her application of these concepts and principles both in her own college classroom and in her research on childhood education. It also explores Miel\u27s notions of the elementary school social studies :urriculum and situates those notions within the context of the conventional wisdom of her day regarding a discipline-centered curriculum.
In a broader context, this study contributes to the body of curriculum history scholarship. According to Kliebard (1992), for example, curriculum history often deals with the relationship between social change and changing ideas and contains significant social and cultural artifacts of knowledge that have become embodied in the curriculum of schools. Davis (1976, 1977) characterizes curriculum history as a reflective enterprise for curriculum workers that contributes to their understanding of present courses of study and of the professional field by lending a framework for thoughtful deliberation of what the schools should teach. With these observations in mind, Miel\u27s work may be understood as both artifact of curriculum history and as mindful reflection, situated within a particular social and historical context, on democratic meanings and processes. Biographies of Caswell, Taba, Tyler, Schwab, Kilpatrick, Rugg, Bobbitt, Zirbes, Stratemeyer, and others have yielded significant insights. In addition, Seguel\u27s study of early curriculum leaders (1966) constitutes an important theoretical contribution to the field. The study of Miel\u27s life and work adds to this body of knowledge
Review: influence of agricultural practices on the dynamics of carbonates in soils
Get PDFEl carbono inorgánico del suelo o SIC (principalmente como CaCO3) es un importante
reservorio de C a nivel global, con una acumulación máxima estimada de 2.3 x 1015 kg
C, siendo la especie de C dominante en el 54% de los suelos en el mundo. Argumentando
una escasa variación en su contenido tras miles de años, se le ha prestado poca
importancia, sin embargo, se han registrado alteraciones en el pool de SIC en el periodo
de décadas producto de labores agrícolas. Las regiones áridas y semiáridas, que
comprenden más del 35% de la superficie terrestre, y donde se encuentra la mayor parte
del carbonato en el suelo, poseen un rol clave en el ciclo global del C, ya que la conversión
a tierras agrícolas generará procesos de acumulación y /o disolución del SIC. La presente
recopilación analizó más de 60 investigaciones científicas relacionadas a los carbonatos
en el suelo, buscando conocer la influencia de las prácticas agrícolas, específicamente
riego, fertilización y labranza, sobre las reservas de SIC, para dilucidar qué procesos
predominan y su posible efecto en el actual escenario de cambio climático. También se
aborda el secuestro de carbono, las morfologías de los carbonatos y los factores y procesos
de formación de suelos ligados a su génesis. Los resultados indican que las labores de
fertilización y uso de correctores del pH tienen un efecto directo sobre la disolución de
carbonatos, liberando enormes cantidades de CO2 a la atmósfera en el mediano plazo. Sin
embargo, la información recopilada respecto al riego y la labranza, no son suficientes para
concluir cuál es el proceso dominante, ni para calcular las tasas de secuestro o liberación
de C. Resulta necesario continuar con las investigaciones de campo, que permitan
esclarecer los alcances de la agricultura en las reservas de SIC a escala global.Soil inorganic carbon or SIC (mainly as CaCO3) is an important global storage of C, with
an estimated maximum accumulation of 2.3 x 1015 kg C, being the dominant C species in
54% of soils in the world. Arguing a little variation in its content after thousands of years,
little importance has been given to it, however, alterations have been registered in the
pool SIC in the period of decades because of agricultural work. Arid and semi-arid
regions, which reach more than 35% of the earth's surface, and where most of the
carbonate is found in the soil, play a key role in the global C cycle, since conversion to
agricultural land will generate processes of accumulation or dissolution of the SIC. This
compilation analyzed more than 60 scientific investigations related to carbonates in the
soil, seeking to know the influence of agricultural practices, specifically irrigation,
fertilization, and tillage, on SIC reserves, to elucidate which processes predominate, and
the possible effect in the current climate change scenario. Carbon sequestration, carbonate
morphologies, and soil forming factors and processes linked to their genesis are also
addressed. The results indicate that the work of fertilization and the use of pH correctors
have a direct effect on the dissolution of carbonates, releasing massive amounts of CO₂
into the atmosphere in the medium term. However, the information collected concerning
irrigation and tillage is not enough to conclude which is the dominant process, nor to
calculate the rates of sequestration or release of C. It is necessary to continue with field
research, which will clarify the scope of agriculture in SIC reserves on a global scale.Versión original del auto
Characterization of ph variation in the soils of the main agroecosystemic soils of Chile
No full textEl cambio climático y las presiones antrópicas han influido en la actual composición química
del suelo, afectando su acidez. Para lograr una gestión óptima y sustentable de los suelos, es
preciso caracterizar su condición. La presente investigación se enfoca en el análisis de la
variación espacial y temporal del pH del suelo en la zona centro-sur de Chile, específicamente
entre las regiones de O'Higgins y Aysén. En primer lugar, se extrajeron los valores de pH de
los estudios Agrológicos del Centro de Información de Recursos Naturales (CIREN) entre
los años 1997 y 2005. Para la caracterización actual del pH, se tomaron muestras entre los
años 2020 y 2023, abarcando áreas similares a los muestreos de CIREN. Posteriormente,
utilizando técnicas de mapeo digital de suelos y modelamiento Random Forest, se evaluó la
relación del pH del suelo con factores ambientales en ambos periodos. Los datos históricos
(CIREN) de pH variaron entre 4,4 y 7,6 (fuertemente ácidos a ligeramente básicos), una
media de 5,89 (ligeramente ácido), y una variabilidad moderada (desviación estándar de
0,55), en tanto los valores de pH actuales variaron entre 3,84 y 7,55 (fuertemente ácidos a
ligeramente alcalinos), una media de 5,78 (ligeramente ácido), y una mayor dispersión que
en el periodo anterior (desviación estándar de 0,66). Existe una importante variabilidad
espacial del pH, con suelos más alcalinos en las regiones centrales y suelos más ácidos en las
zonas del sur, con una precisión de 0,72% en ambos casos. Se observó un ligero aumento de
los valores de pH en algunas áreas del sur como en las comunas de Chiloé, Aysén y Capitán
Prat, y una disminución o acidificación en los sectores de Cachapoal, Ñuble, Linares y
Concepción. Por el contrario, la variación temporal no presenta diferencias significativas
pero cabe señalar que estos análisis consideran los valores de pH sin considerar su ubicación
e el espacio. El mapeo digital de suelos es una herramienta efectiva para la caracterización
del pH y otras propiedades edáficas, destacando la necesidad de más datos para mejorar la
precisión en áreas con mayor incertidumbre, como las zonas montañosas y del extremo sur.Climate change and anthropogenic pressures have influenced the current chemical
composition of the soil, affecting its acidity. To achieve optimal and sustainable soil
management, it is essential to characterize its condition. In this context, the present study
focuses on analyzing the spatial and temporal variation of soil pH in central-southern Chile,
specifically between the regions of O'Higgins and Aysén. First, pH values were extracted
from the Agrological Studies of the Center for Natural Resources Information (CIREN)
between 1997 and 2005, with values ranging from 4,4 to 7,6 (strongly acidic to slightly
basic), an average of 5,89 (slightly acid), and moderate variability (standard deviation of
0,55). For the current characterization of soil pH, samples were taken between 2020 and
2023, with pH values ranging from 3,84 to 7,55 (extremely acidic to slightly basic), an
average of 5,78 (slightly acid), and greater dispersion compared to the previous period
(standard deviation of 0,66). Subsequently, using digital soil mapping techniques and
Random Forest modeling, the relationship between soil pH and environmental factors was
evaluated for both periods. The results show significant spatial variability in soil pH, with
more alkaline soils in central regions and more acidic soils in the southern areas, with an
accuracy of 0,72% in both cases. A slight increase in pH values was observed in some
southern areas, such as the communes of Chiloé, Aysén, and Capitán Prat, while a decrease
or acidification was noted in Cachapoal, Ñuble, Linares, and Concepción. Conversely, the
temporal variation does not present significant figures according to the variance analyses
performed. However, it is important to note that these analyses consider pH values without
accounting for their spatial location. The study concludes that digital soil mapping is an
effective tool for characterizing soil pH and other edaphic properties, highlighting the need
for more data to improve accuracy in areas with higher uncertainty, such as mountainous and
southern regions.Versión original del auto
Seasonal assessment of soil hydrophobicity in two hillside of the sclerophyllous forest remnants of the O'Higgins Region
Get PDFLa repelencia del suelo a la humectación por agua es un factor relevante para entender los procesos hidrológicos, como la erosión o la capacidad de almacenamiento de agua, sobre todo en un contexto de cambio climático y sequías en un clima mediterráneo como la zona central de Chile. Se analizaron 144 muestras de suelo colectadas bajo la influencia de cuatro especies arbóreas dominantes en dos remanentes (exposiciones) del bosque esclerófilo, recopiladas en invierno y primavera en Malloa y San Vicente (Región de O’Higgins). Se determinó si las muestras de suelo presentan carácter hidrofóbico o hidrofílico a través del Índice de Repelencia (R) y se analizó su relación con propiedades físicas del suelo. De los factores del estudio (4 especies arbóreas, 2 sitios, 2 fechas) diez de los dieciséis valores de R son hidrófobos, es decir, presentan repelencia al agua, dominantemente en época de invierno y bajo Peumus boldus; por su parte, Escallonia pulverulenta es la única especie que presentó valores cercanos a la hidrofilia. La fecha de muestreo fue la única variable que presentó efecto significativo sobre los valores de R (p=0,0408), con una mayor repelencia en invierno. Respecto al análisis de componentes principales, este logró discriminar los sitios (exposiciones), posiblemente debido a un efecto textural. Los suelos muestreados de la zona central de Chile presentan un comportamiento predominantemente hidrofóbico, sin embargo, es necesario continuar estudiando el efecto del contenido de materia orgánica y la textura del suelo sobre la repelencia al agua en suelos de Chile.The soil repellency to wetting by water is a relevant factor to understand hydrological processes, such as erosion or the water storage capacity, especially in a context of climate change and droughts in a Mediterranean climate like the central zone of Chile. 144 soil samples were collected and analyzed under the influence of four dominant tree species in two remnants (Slope exposure) of the sclerophyllous forest, collected in winter and spring in Malloa and San Vicente (O'Higgins Region). It was determined if the soil samples have a hydrophobic or hydrophilic character by the Repellency Index (R), analyzing its relationship with soil physical properties. Ten of the sixteen factors of the study (4 tree species, 2 sites, 2 seasons) show R values considered as hydrophobic, thus, they present water repellency, predominantly in winter and under Peumus boldus; On the other hand, Escallonia pulverulenta is the only species that presented values close to hydrophilicity. The sampling date was the only variable that showed a significant effect on the R values (p=0.0408), with the highest repellency in winter. The principal component analysis discriminated well between the sites (slope exposures), possibly due to a textural effect. The soils sampled from the central zone of Chile has a predominantly hydrophobic behavior; however, it is necessary to continue studying the effect of the organic matter content and soil texture on water repellency in Chilean soils.Versión original del auto
Snow cover analysis of the Aysen river basin from satellite images and in-situ data
Get PDFEl calentamiento global (del sistema climático) ha sido evidenciado a través de varias respuestas, como la contracción de glaciares, el retroceso del hielo marino, el aumento del nivel del mar y de la temperatura del aire, entre otras. La magnitud de estos cambios tiende a ser crítica sobre biomas extremos y prístinos. La Patagonia de Chile es una de las regiones más inhabitadas y prístinas en el mundo, así como un importante reservorio de agua dulce en un entorno de bosques perennes, lagos y fiordos. Al mismo tiempo, esta región presenta escasos y débiles registros de mediciones in-situ de variables ambientales, por lo que es necesario emplear información satelital para estimar las tendencias de parámetros biofísicos. El objetivo principal de esta memoria es evaluar la cobertura nival de la cuenca del río Aysén usando imágenes MODIS en el período 2002-2016. El producto MOD10 fue procesado a una resolución espacial de 500 x 500 m2 a escala diaria y se realizó una interpolación de pixeles sin información mediante la combinación de imágenes de los satélites TERRA y AQUA y la aplicación de un filtro temporal y espacial para obtener una aproximación de la cobertura nival. El análisis de la serie de tiempo consistió en el test no-paramétrico de Mann-Kendall y Sen's slope de la media estacional y anual del área de la cobertura nival (SCA). La red de estaciones meteorológicas y fluviométricas disponibles en el área de estudio fue utilizada para comparar la cobertura nival con las tendencias de la temperatura del aire, precipitación y caudales en la última década. Los resultados indican que la cobertura nival presenta una tendencia decreciente de la media anual de SCA de 25,11 km2⋅año-1 sin significancia estadística, sin embargo, si se considera los últimos doce años del periodo, la tendencia presenta significancia a una tasa de 69,17 km2⋅año-1. La comparación con datos in-situ muestra una tendencia al aumento de la temperatura media del aire y la disminución de precipitaciones y caudales, situando al año hidrológico 2016-17 como el año con anomalías estandarizadas conjuntas más negativas en el periodo. Sin embargo, la falta de estaciones in-situ de monitoreo de altura de nieve y la presencia de la cobertura nubosa sobre la cuenca pueden impactar las tendencias, generando algunas incertidumbres en los datos. Finalmente, esta memoria contribuye inicialmente a analizar los posibles impactos del calentamiento global evidenciado por la cobertura nival en la Patagonia de Chile.Global warming (of climatic system) has been evidenced in several responses such as glacier shrinkage, sea ice retreat, sea level rise and air temperature increase, among others. The magnitude of these changes tends to be critical over pristine and extreme biomes. Patagonia-Chile is one of the most pristine and inhabited regions in the world gathered the most important fresh water reservoirs in addition to evergreen forest, lakes and fiords. Furthermore, this region presents a scarce and weak ground stations network which must be combined to satellite information to retrieve trends on biophysical parameters. The main objective of this work is to present the first assessment on snow cover over Aysen basin in Patagonia-Chile by using MODIS data from 2002-2016 period. MOD10 product was processed at 500 x 500 m2 spatial resolution for daily basis with a no data pixels interpolation by a TERRA and AQUA images combination and a temporal and spatial cloud filter was applied to obtain a proxy indicator of snow cover. Time series analysis consisted on no-parametric test such as Mann-Kendall and Sen's slope were used in this work at seasonal and annual mean of snow cover extent (SCA). Ground meteorological network and river discharges data were also included in this work to reveal the trends of air temperature, rainfall and stream flow during the last decade. Results indicate that snow cover shows a decreasing trend in anual mean SCA of 25,11 km2⋅year-1 with no statistical significance, however, considering the last twelve years of the period, the trend has a significance with a decreasing slope of 69,17 km2⋅year-1. The comparison with in situ data shows a trend to increase the mean air temperature and the decrease of precipitations and stream flows in the period, placing the hydrological year 2016-17 as the year with more negative standard joint anomalies in the period. However, the lack of in-situ snow depth monitoring stations in addition with the persistence of cloud cover over the basin can impact trends, creating some uncertainties in the data. Finally, this work contributes initially to analyze the possible impacts of the global warming evidenced by the snow cover in the Chilean Patagonia.Versión original del auto
Air quality data of station Congonhas, São Paulo from 2014-2020
No full textWe compiled criteria pollutants from four air quality monitoring stations in Bogotá, eight in Santiago, and five in São Paulo to characterize the impact of emission changes on air quality during the early Coronavirus-imposed lockdown. Time series include hourly measurements (UTC) of ozone (ppbv), nitric oxide (ppbv), nitrogen dioxide (ppbv), carbon monoxide (ppmv), and PM2.5 (microgram per cubic meter), from 1 January 2014 to 1 June 2020.
Specifically, datasets were used to compare the lockdown period (March-May 2020) with the baseline period defined as the multi-year average between 2014 and 2019.
São Paulo's air quality data were downloaded from the website of the official monitoring network (https://qualar.cetesb.sp.gov.br). The data provided correspond to the following stations: Congonhas, Ibirapuera, Ponte dos Remedios, Parque Dom Pedro, and Pinheiros
Air quality data of station Carvajal-Sevillana, Bogotá from 2014-2020
No full textWe compiled criteria pollutants from four air quality monitoring stations in Bogotá, eight in Santiago, and five in São Paulo to characterize the impact of emission changes on air quality during the early Coronavirus-imposed lockdown. Time series include hourly measurements (UTC) of ozone (ppbv), nitric oxide (ppbv), nitrogen dioxide (ppbv), carbon monoxide (ppmv), and PM2.5 (microgram per cubic meter), from 1 January 2014 to 1 June 2020.
Specifically, datasets were used to compare the lockdown period (March-May 2020) with the baseline period defined as the multi-year average between 2014 and 2019.
Bogotá air quality data were provided by the air quality monitoring service of the city's Environmental Agency (http://201.245.192.252:81/). The monitorng stations includes: Carvajal-Sevillana, Centro de Alto Rendimiento-CDAR, Guaymaral, and Tunal
Air quality data of station Guaymaral, Bogotá from 2014-2020
No full textWe compiled criteria pollutants from four air quality monitoring stations in Bogotá, eight in Santiago, and five in São Paulo to characterize the impact of emission changes on air quality during the early Coronavirus-imposed lockdown. Time series include hourly measurements (UTC) of ozone (ppbv), nitric oxide (ppbv), nitrogen dioxide (ppbv), carbon monoxide (ppmv), and PM2.5 (microgram per cubic meter), from 1 January 2014 to 1 June 2020.
Specifically, datasets were used to compare the lockdown period (March-May 2020) with the baseline period defined as the multi-year average between 2014 and 2019.
Bogotá air quality data were provided by the air quality monitoring service of the city's Environmental Agency (http://201.245.192.252:81/). The monitorng stations includes: Carvajal-Sevillana, Centro de Alto Rendimiento-CDAR, Guaymaral, and Tunal
Air quality data of station Ponte dos Remedios, São Paulo from 2014-2020
No full textWe compiled criteria pollutants from four air quality monitoring stations in Bogotá, eight in Santiago, and five in São Paulo to characterize the impact of emission changes on air quality during the early Coronavirus-imposed lockdown. Time series include hourly measurements (UTC) of ozone (ppbv), nitric oxide (ppbv), nitrogen dioxide (ppbv), carbon monoxide (ppmv), and PM2.5 (microgram per cubic meter), from 1 January 2014 to 1 June 2020.
Specifically, datasets were used to compare the lockdown period (March-May 2020) with the baseline period defined as the multi-year average between 2014 and 2019.
São Paulo's air quality data were downloaded from the website of the official monitoring network (https://qualar.cetesb.sp.gov.br). The data provided correspond to the following stations: Congonhas, Ibirapuera, Ponte dos Remedios, Parque Dom Pedro, and Pinheiros
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