1,721,002 research outputs found
Effect of tillage system and crop residue management on soil carbon content of a luvisol and its effect on wheat response to nitrogen under rainfed mediterranean conditions
No full textUnder Mediterranean conditions, soils under conventional tillage farming usually have very low contents of organic matter. This situation is due to intensive soil tillage, low biomass production under rainfed conditions, and removal of cereal straw for alternative use off the field. The effect of no-till (NT) on the soil organic carbon (SOC) seems to be depended on the conditions but positive effect of NT on SOC is referred by authors working in regions, like the Mediterranean, were the organic content of the soil under the conventional tillage system (CT) is low (usually below 7 g C kg-1 of soil), whereas the absence of effect is referred from authors developing the work in wetter and cooler regions, where values of SOC under the traditional tillage systems are higher (usually above 1.2 g C kg-1 of soil).
The effect of nitrogen fertilization on SOC is well documented with the results varying with conditions. However the information of long term effects of tillage and crop residues management on the crop response to nitrogen fertilization is missing.
The objectives of this paper are to analyse long term effects of tillage systems and crop residue management on SOC under Mediterranean conditions and its effect on wheat yield response to nitrogen
Efeitos da mobilização do solo no destacamento de partículas de solo pelo impacto das gotas de água da chuva, escoamento superficial e erosão laminar, na cultura do trigo, num solo franco-argilo-limoso
No full textUm ensaio de campo foi conduzido por forma a avaliar os efeitos dos sistemas de mobilização tradicional (MT), reduzida (IVIR) e sementeira directa (SD) sobre o destacamento de partículas de solo pelo impacto das gotas de água de chuva, o volume de escoamento superficial, e a massa de sedimentos transportados em suspensão. Decorreu num ensaio de mobilizações para a cultura do trigo, com 3 anos, em blocos casualizados com 3 tratamentos e 3 repetições, com chuva natural, durante o Inverno de 1998/99, num solo franco-argilo-limoso com 5 % de declive. A medição do destacamento, foi realizado com funis preparados para o efeito, com 20 cm de diâmetro, e o escoamento superficial em talhões com 2 m2. Alguns parâmetros físicos e químicos do solo foram medidos por forma a descrever as diferenças induzidas pelos diferentes sistemas de mobilização na superfície do solo. A cobertura do solo pelos resíduos foi medida antes da 1' chuvada tanto em termos de massa como de percentagem de área coberta. Das 15 chuvadas registadas apenas 7 produziram escoamento superficial. A massa média de partículas destacadas foi sempre superior com a MT, seguido pela MR (38,8 a 87,4 % da massa média com a MT) e a SD (5,9 a 57,1 %). Os resultados sugerem que as diferenças encontradas entre as superfícies mobilizadas têm origem nas diferentes percentagens de área coberta pelos resíduos, e na estabilidade dos agregados e crosta, resultante de diferentes teores de matéria orgânica. Não foram encontradas diferenças em termos de densidade aparente ou de resistência do solo à penetração entre as superfícies mobilizadas, sendo os valores para a SD muito mais elevados. A energia cinética da chuva, necessária para destacar 1 g de solo, aumentou da la chuvada para as seguintes, devido à formação de crosta nas superfícies mobilizadas, aumentando mais
tarde, à medida que a cobertura proporcionada pela canopia aumentava. A energia cinética total de uma chuvada aparentemente fornece melhores resultados na predição da massa total de material destacado que o índice de erosividade EI30. Embora o efeito dos diferentes sistemas de mobilização para o 1° evento chuva/escoamento superficial não tenha sido estatisticamente significativo, mesmo para P=0,10, foi observada uma tendência: a SD teve o maior volume de escoamento superficial, seguido da MR (64% da quantidade média de SD) e da MT (52%). Esta tendência desapareceu nos eventos subsequentes, aparentemente o desenvolvimento da crosta superficial teve um efeito tão importante quanto a camada superficial naturalmente compactada do tratamento SD no controlo da infiltração. A massa total de sedimentos transportados em suspensão na água que constituiu escoamento superficial, no cômputo das 7 chuvadas, foi maior com a MT, seguido da MR (69% da quantidade com a MT) e da SD (40%). No entanto, se analisarmos chuvada a chuvada, a massa de sedimentos transportados seguiu padrões diferentes. A concentração dos sedimentos foi
sempre maior com a MT, a MR apresentou 43 a 86% da concentração média com a MT, eaSD22a53%. A medição da massa de material destacado permitiu destrinçar o destacamento do transporte e, assim, reconhecer diferenças entre os sistemas de mobilização que de outra forma passariam despercebidas. Este trabalho mostra que a redução da intensidade da mobilização pode conduzir a uma redução na massa de material destacado, para além da simples diferença no grau de cobertura proporcionado pelos resíduos, significando uma redução no transporte de sedimentos em suspensão na água do escoamento superficial, em especial nas situações em que a capacidade de transporte do escoamento superficial não é o factor restritivo no processo erosivo.
***Summary - A field trial was carried out in order to assess the effects of the traditional, reduced and no tillage systems on soil detachment by raindrop impact, overland flow volume and sediment load. It was conducted on a 3 years old wheat crop tillage trial (with a randomized design for 3 treatments with 3 replicates, i.e. 9 plots), under rain fed conditions, during the winter of 1998/99, on a clay loam with a 5% slope. Splash was measured with splash-funnels with 20 cm in diameter, and overland flow on 2 m2 plots. Selected physical and chemical parameters were measured in order to describe tillage-induced differences in the surface soil. Soil residue cover was measured prior to the first rainfall event both in terms of mass and percent cover. From the 15 rainfall events only 7 produced runoff. Average splash detachment was always higher under traditional tillage, followed by reduced tillage (38.8 to 87.4 % of the average amount under traditional tillage) and no-tillage (5.9 to 57.1 %). The results suggest that the differences found between the tilled surfaces are due to the residues and the different aggregate and crust stability, induced by different organic matter contents under each tillage system. No differences were found in terms of dry bulk density or soil penetration resistance between the tilled surfaces. The kinetic energy of the rainfall needed to splash 1 g of soil per m2 followed a growth pane, at a first stage, as a seal was formed on the tilled surfaces, and later as the canopy cover increased. The total rainfall kinetic energy apparently provides a better mean to predict total soil detachment than the EI30. Though the effect of the tillage treatments for the first rainfall/runoff event was not statistically significant, even at 0,10 level, the following trend could be observed: no-tillage had the highest runoff volume, followed by reduced tillage (64% of the average amount under no-tillage) and traditional tillage (52%). This trend disappeared in subsequent events, which
suggests that soil seal development had as much of an effect as the naturally compacted surface layer of the no-tillage treatment in controlling infiltration. Total sediment load over the 7 events was highest under traditional tillage, followed by reduced tillage (69% of the average amount under traditional tillage) and no-tillage (40%). Nevertheless, differences in the sediment load on an event basis followed different patterns. Sediment concentration was awl s higher under traditional tillage; reduced tillage had 43 to 86% of the average Y concentration under traditional tillage, and no-tillage 22 to 53%. The measurement of particle detachment by raindrops allowed unravelling detachment from transport and thus recognizing differences between the tillage systems that would otherwise pass unnoticed. This work shows that the reduction in tillage intensity may leal to a reduction in the sediment load, especially in situations where the sediment transport capacity of the overland flow is not the restrictive factor for erosion
Interacção do sistema de mobilização do solo e do regime hídrico na produção do girassol
Full text linkEstudos realizados em diferentes tipos de solo no Alentejo mostraram que com a redução da intensidade de mobilização do solo, especialmente através da sementeira directa, se obtém produções para as culturas arvenses de sequeiro de Outono-Inverno semelhantes às do sistema tradicional. Verificou-se, no entanto, a existência de uma interacção significativa entre o solo, os sistemas de mobilização e as condições meteorológicas, nomeadamente na cultura do girassol. Uma possível explicação para as limitações à sementeira directa em culturas de Primavera de sequeiro, está provavelmente associada a uma maior resistência do solo à penetração das raízes, em particular nos solos mal estruturados e com teores de humidade muito variáveis em função da precipitação primaveril. A fim de testar esta hipótese, realizou-se um ensaio que iria permitir estudar a interacção do sistema de mobilização do solo com vários regimes hídricos na produção do girassol, optando-se no factor mobilização do solo pelo estudo dos dois extremos em termos de intensidade, isto é, mobilização tradicional e sementeira directa. Procedeu-se à avaliação dos efeitos destes dois factores nas propriedades físicas do solo, no crescimento radical, no crescimento da cultura e na produção de matéria seca total e de grão. Com o objectivo de facilitar e tornar mais expedita a determinação do comprimento das raízes desenvolveu-se, no âmbito deste trabalho, um método original de medição de raízes (programa MedeRaizV 1), podendo este ser consultado e utilizado a partir da disquete em anexo. Devido à Primavera de 1997 ter registado precipitações elevadas, somente o regime hídrico mais elevado se diferenciou dos outros dois regimes em termos da produção de grão de girassol. As diferenças observadas entre a sementeira directa e o sistema tradicional foram significativas, apresentando este último valores um pouco mais elevados. No que diz respeito à interacção entre sistemas de mobilização e regimes hídricos, o sistema tradicional apenas se destacou positivamente da sementeira directa no regime hídrico 3, devido a um elevado
número de grãos por m2 e a um peso relativamente elevado de mil grãos, o que indica que houve outros factores limitativos nos talhões não mobilizados para além da água disponível. Tanto os rendimentos finais da cultura nos diferentes tratamentos, como o desenvolvimento da cultura ao longo do seu ciclo, registado através da evolução do índice de área foliar e da matéria seca, mostraram que existiram maiores limitações na sementeira directa no que respeita à exploração dos recursos pelo sistema radical. Apesar da grande disponibilidade de água no início do ciclo e das pequenas diferenças em termos de nutrientes disponíveis no solo, observaram-se, logo após a emergência, menores taxas de crescimento na sementeira directa. As medições da resistência à penetração bem como, mais tarde, a determinação da densidade e distribuição das raízes confirmaram a maior dificuldade no crescimento radical neste sistema de mobilização. O facto de ter havido uma diferenciação em termos de produção entre os dois sistemas de mobilização apenas no regime hídrico 3, indica que a água se tornou o factor mais limitante no final do ciclo nos outros 2 regimes hídricos, permitindo nestes uma recuperação da cultura sob sementeira directa devido a um menor consumo de água antes da floração. Ao mesmo tempo pode-se concluir que em solos mal estruturados mesmo um elevado teor de água no solo, no caso da não mobilização, não consegue atenuar suficientemente a resistência à penetração, a fim de permitir um crescimento radical comparável às condições existentes após a mobilização. Assim as vantagens económicas e agronómicas da sementeira directa para estas culturas parecem estar um pouco restringidas a solos bem estruturados.
### Summary - Studies on several soil types of the Alentejo show that in autumn sown arable crops under rainfed conditions the reduction of the tillage intensity, including direct drilling, results in similar yields as compared to the traditional tillage system. However, a pronounced interaction between soil types, tillage system and weather conditions can be observed in summer crops, especially sunflower. A possible explanation for these limitations under no-tillage in rainfed summer crops could be a higher penetration resistance for the roots, especially on badly structured soils with a great variation in soil moisture as a result of the precipitation in spring. In order to study these relationships a trial was installed to analyses the interaction of the tillage system and the soil moisture regime on the performance of sunflower, comparing the traditional and the no-tillage system as the two extremes in terms of tillage intensity. The effects of these two factors on the physical soil properties, root and crop development and total and seed dry matter yield were analysed. In order to facilitate and accelerate the measurements of the root length of a considerable number of root samples, a new root measurement method (MedeRaizV1) was developed, which can be consulted and applied using the program attached to this thesis. Due to the unusual precipitation in spring 1997, only the highest irrigation level differed from the two others in terms of the seed yield of sunflower. Traditional tillage showed significantly higher yields as compared to no-tillage. Regarding the interaction between tillage system and water regime, only the traditional tillage system under the highest moisture regime yielded significantly better due to a higher number of seeds per m2 and a higher grain weight, indicating that there were other limiting factors than water availability under no tillage. Both the final yields under the different treatments and the development of the crop during its vegetation period, determined through leaf area and dry matter measurements, showed that there must have been greater limitations under no-tillage in what the exploitation of the soil through the roots is concerned. Despite the high water availability in the beginning of the season and the small differences in available nutrients, reduced growth rates of the crop under no-tillage could be observed right after emergence. Measurements of the penetration
resistance as well as the determination of the root density and distribution confirmed the increased difficulties for the root growth under this tillage system. The fact that the differentiation in terms of grain yield between the two tillage systems only occurred in the highest moisture regime indicates that water became the limiting factor at the end of the season under the two other moisture regimes, allowing a recovery of the crop under no-tillage due to a reduced water consumption before flowering. It can also be concluded that on badly structured soils high soil moisture content is not enough to decrease penetration resistance sufficiently under no-tillage, in order to enable a root growth similar to the conditions under ploughing. Therefore, it seems that for summer crops the economical and agronomic advantages of no-tillage are somehow restricted to well-structured soils
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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