1,721,004 research outputs found
Weed Diversity Under Different Water Regimes in Irrigated Direct-Seeded Rice Cultivation
Get PDFThis study comprised two sets of experiment. The field trials were conducted at MARDI Bertam Rice Research Station in Seberang Perai, Penang, while the experiments on weed seed viability were done in a glass house and the Weed Biology Laboratory at Universiti Putra Malaysia. This study began in February 2004 and ended in June 2006. All field trials and weed seed viability studies were done in Off Season 2004 and Main Season 2004/2005. The objectives of the study were: a) to investigate the population and status of dominant weeds and their effect on rice yield under different water regime treatments in field condition; b) to determine the total weed seed reserve, species composition of the entire weed seed bank in the soils and their viability after being treated under different water regime treatments in the rice field.
Five water regime treatments were used namely; T1 = continuous flooded condition until maturity, T2 = early flooding until 55 DAS (day after sowing) followed by saturated condition until maturity, T3 = early flooding until 30 DAS followed by saturated condition until maturity, T4 = continuous saturated condition until maturity, T5 = continuous field capacity condition throughout the experiment period.
Results from field trials indicated that in unweeded plots (no weed control treatment involved), T1 and T2 showed the lowest number of weed m-2 and weed biomass m-2 compared to the other water regime treatments. Plots treated with T1 and T2 significantly suppressed weed population to approximately 18 – 58% and reduced weed biomass to 14 – 57% as compared to the highest in T5 at all sampling dates (30, 60 and 90 DAS) in both Off Season 2004 and Main Season 2004/2005. For weed composition across the water regime treatments, 11 weed species were recorded in Off Season 2004 and 10 weed species in Main Season 2004/2005. Broadleaved weeds mostly Monochoria vaginalis and Limnocharis flava were the most dominant weeds in most of the water regime treatments. The SDR values of broadleaved weeds were 48.7% (T2) > 46.4% (T1) > 44.2% (T3) > 40.7% (T5) > 35.8% (T4) in Off Season 2004. In Main Season 2004/2005, the SDR values for broadleaved weeds increased to 79.5% (T2) > 68.2% (T1) > 62.4% (T3) > 62.2% (T4) > 50.57% (T5). Sedges mainly Fimbristylis miliacea and Cyperus iria were dominant in Off Season 2004 with SDR value more than 34% in all water regime treatments, but decreased to less than 23% in Main Season 2004/2005. For grasses, mostly Echinochloa crus-galli, Echinochloa colona and Leptochloa chinensis, SDR value more than 20% were recorded in T4 and T5 in Off Season 2004 while in Main Season 2004/2005, SDR value between 21 – 34% were observed in T1, T3 and T5.Meanwhile rice plants treated with T1 significantly produced the highest rice grain yield, followed by T2 and T3, while T4 and T5 were the lowest in weeded plots in both planting seasons. However, rice yield in unweeded plots were not significantly different in all water regime treatments. The rice productions in weeded plots were in the range of 22 – 60% higher in Off Season 2004 and 56 – 78% higher in Main Season 2004/2005 than in unweeded plots. Weed control treatment evidently showed stronger influence than water regime treatments. The percentages of reduction in weeded plots from the highest rice yield in T1 to lowest in T5 were 40% in Off Season 2004 and 44.4% in Main Season 2004/2005. Meanwhile the reduction of rice yield in unweeded plots compared to weeded plots was much higher, which recorded the highest of 59.1% (in T1) in Off Season 2004 and 78.3% (in T4) in Main Season 2004/2005.
The effect of different water regime treatments on viability of weed seeds in rice field was evaluated. Total weed seed reserves in soils taken from Off Season 2004 rice plots were dominated by broadleaved weeds (90625 seeds m-2) mainly Hedyotis corymbosa, Monochoria vaginalis and Ludwigia hyssopifolia, followed by sedges (34257 seeds m-2), mostly F. miliacea and Cyperus iria, while grasses (20647 seeds m-2), predominantly Leptochloa chinensis recorded the lowest number in all water regime treatments. In soils taken from Main Season 2004/2005 rice plots, sedges (53041 seeds m-2) mainly Fimbristylis miliacea along with broadleaved weeds (54624 seeds m-2), predominantly Monochoria vaginalis and Ceratopteris pteridoides dominated in most of the water regime treatments, while grasses, mainly Leptochloa chinensis and Panicum repens again recorded the lowest number (24935 seeds m-2). 10 weed species, which were not observed in the field trials, were recorded from the same soil in the weed seed bank experiment.Differences in water regime treatments did not significantly reduce the viability of weeds seeds in the soil in Off Season 2004. However, a small reduction in seed viability (approximately 8%) was observed in Main Season 2004/2005. As for the similarity between weed seed bank composition and aboveground weed flora composition, a moderate value (62.07 - 73.33%) was observed in Off Season 2004, while in Main season 2004/2005, the value was slightly lower (51.65 – 64.29%)
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
Get PDFWe 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
Occurrence and management of resistant weed species in FGV plantation in Malaysia : a review
No full textOil palm, currently the world’s main vegetable oil crop, is characterized by a large productivity and a long life span (25 years). Weeds are the unwanted plants that grow aggressively, restrict sunlight and compete with desirable plants for nutrients. Weeds population is mainly a mixture of grasses, sedges, broad-leaved weeds plants and fernsin oil palm plantation management. Asystasia gangetica (creeping broad leaf weed), Clidermia hirta (upright woody weed) and Dicranopteris linearis (fern) are amongst noxious weeds under the “must be eradicated”list because of their high tendency to aggressively absorb nutrients and water. In Malaysia alone, since 2004, the use of herbicides has been 67.49% of the total pesticides used. The application of herbicides (e.g. glyphosate, glufosinate, metsulfuron-methyland the recently banned paraquat) in plantations is a common practice even though farmers understand that they are harmful to both applicators and crops if not carefully used. Understanding the mode of herbicidal action is also very useful when diagnosing symptoms of herbicide injuries and to reduce the risk of resistance development in weed populations. Resistance frequently occurs with herbicides that come with very great efficacy to specific weed species, be it acute kill or chronic/slow effect. Herbicide resistance phenomenon in weeds is very depending on the type of herbicides being used (mode of action and selectivity), the period they have been used for, spray dose of the herbicides, the residual effect of the herbicides, the biology and genetic of the weed species being targeted, and existence of other crop management practices that farmers employ.Therefore, weed resistance in Malaysian oil palm plantation is crucial and must be hadle with care to avoid unnecessary effect from herbicide resistance
Corn growth, yield and weed composition as influenced by different nitrogen rates and plant densities
No full textSufficient nitrogen application is the main factor in plant growth and yield development processes. Therefore, a field research was conducted during 2020 at Field 15, Faculty of Agriculture, Universiti Putra Malaysia in Serdang, Selangor, to quantify the effect of four nitrogen rates N1 (120 kg N/ha), N2 (140 kg N/ha), N3 (160 kg N/ha) and N4 (180 kg N/ha) and two planting densities D1 (75 x 20 cm) and D2 (65 x 20 cm) on growth and yield attributes of corn variety (GWG 888) and weed composition. The results showed that both factors (nitrogen rates and planting densities) significantly influenced corn growth, yield and weed composition. It was observed that N3 (160 kg N/ha) produced the maximum plant height, number of leaves, cob number, cob length and dry mater yield. The maximum number of the weed species and weed population were obtained with 180 kg N/ha. Higher plant density (65 x 20 cm) decreased plant height and leaf; however, it significantly enhanced dry matter yield. The findings suggested that the use of 160 kg N/ha was appropriate nitrogen rate at 75 x 20 cm, which improved corn growth and yield
The impact of carbon dioxide (co2) enrichment on rice (Oryza sativa l.) production: a review
No full textRice (Oryza sativa L.) is one of the world's most important crops and the primary source of calories for more than three
billion people worldwide, especially in Asia. Currently, atmospheric carbon dioxide (CO2) concentration is 416 µmol mol-1 and increasing rapidly due to industrialization, which is the main cause of global warming. Current climate change and rising CO2 concentration in the atmosphere have varying global impacts on crop performance. As CO2 is one of the limiting factors in photosynthesis, adding this gas can increase carboxylation activity, hence increasing productivity and yield. Elevated CO2 (eCO2) significantly impacted C3 crops' productivity by increasing photosynthesis, biomass, and grain yield. Plants cultivated under eCO2 conditions demonstrated better development and photosynthesis, lower transpiration, improved water efficiency, decreased inorganic nutrition concentration, increased plant hormone, and compact stomatal density than the plants grown under ambient CO2 (aCO2) conditions. This review discusses the effects of eCO2 on rice plant photosynthesis and growth. The review also describes that eCO2 increased yield components of rice plants. Finally, the current review emphasizes the grain quality of rice that was negatively affected by eCO2. The review paper aims to describe rice production under CO2
increases under climate changes in the future. The synthesis of all this information is helpful to the researchers, advisors of rice farmers, and policymakers to provide a favourable plan by using eCO2 to increase rice plant growth and yield and maintain grain quality through enriching free-air CO2 enrichment (FACE) system for the rice plant to produce enough, and high-quality food for the increasing population of the world
- …
