1,720,992 research outputs found
Fertiliser value of biogas slurry for maize and dry bean production and its effect on soil quality and carbon dioxide emissions.
Full text linkDoctoral Degree. University of KwaZulu-Natal, Pietermaritzburg.Abstract available in pdf
Variability of radiation balance in sloped terrains and its impact on microclimatic characteristics of field crops.
No full textDoctor of Philosophy in Agrometeorology. University of KwaZulu-Natal, Pietermaritzburg, 2018.Abstract available in PDF file
Nitrogen and phosphorus release and potential fertiliser effects of biogas slurry on spinach yield.
No full textMasters Degree. University of KwaZulu-Natal, Pietermaritzburg.Use of organic waste to produce biogas aids in waste management and produces organic residue, biogas slurry (BGS), with appreciable quantities plant nutrient and potential to improve soil productivity. Feedstock and retention time during anaerobic digestion influence the quality and fertilizer value of the biogas Slurry. The objective of the study was to determine the release nutrients of biogas slurry, its potential as nitrogen (N) source and effects of co-application with chemical fertilizer (CF) on spinach yields and soil chemical parameters. Samples of biogas slurry, produced from cattle dung, and cattle manure (CM) were collected from Qwa-qwa, in the Free State Province of South Africa. The samples were analysed for pH, electrical conductivity (EC), total carbon (C), nitrogen, phosphorus (P), exchangeable bases and trace elements. Dried biogas slurry and cattle manure were applied to Avalon and Hutton soils at 0, 1, 2 and 3% (w/w). Then moistened to field capacity moisture, and incubated for 8 week, with periodic moisture correction. Destructive sampling was used to collect soil samples at 0, 1, 2, 4 and 8 weeks and the samples were analysed for pH, electrical conductivity, ammonium and nitrate-nitrogen, available phosphorus and exchangeable bases. Three glasshouse experiments were conducted to determine the fertiliser value of BGS for spinach (Spinacia oleracea) grown for 8 weeks. In the first experiment, biogas slurry was compared with chemical fertilizer and cattle manure as nitrogen sources at 100 kg N/ha in the Avalon soil. The second experiment involved application of biogas slurry and cattle manure at increasing nitrogen application rates of 0, 100, 150, 200 and 250 kg N/ha in Avalon soil. While the third experiment involved co-application of biogas slurry with chemical fertilizer at 0/100, 40/60, 60/40 and 100/0 kg N/ha (BGS/CF) in Avalon and Hutton soils. Soil pH increased with increasing application rate on both soils, during incubation. The 1% application rate showed the least pH increase for Hutton soil, which was significantly higher by 1.89% for cattle manure and 3.70% for biogas slurry than the control at week 8. Ammonium-N declined by 73.6% in Avalon compared to the 36.7% in Hutton soil at 3% BGS NH4-N within 2 weeks, then increased steadily up to week 8 at all application rates for both soils. On the other hand, nitrate-nitrogen declined for biogas slurry and increased for cattle manure, with increasing application rate after 2, 4 and 8 weeks of incubation in both soils. Available phosphorus increased with increasing rate of both biogas slurry and cattle manure especially up to two weeks of incubation in soils. Spinach dry matter yield were comparable between biogas slurry (4.04 g/pot) and cattle manure (3.40 g/pot) as a nitrogen sources, even though greater nutrient uptake and soil residual fertility occurred in BGS treatment. Increasing application of biogas slurry and cattle manure increased spinach dry-matter (DM) accumulation significantly from 100 up to 150 kg N/ha by 32.9% for biogas slurry and 23.1% for cattle manure, beyond that rate there was no notable variation. Higher nutrient uptake was observed at 150 kg N/ha, which supports the higher yields. However, biogas slurry co-application with chemical fertilizer had no synergistic effect and increasing application rate showed no significant improvement in dry matter yield and nutrient uptake. The findings of the study implied that the fertiliser value of biogas slurry was similar to cattle manure and subsequent crop could benefit from residual fertility after biogas slurry and cattle manure.The fourth supervisor (M. Moeletsi) is acknowledged on page iii of the thesis
Heat production and seedling vigor of germinating soybean seeds
Full text linkMeasuring the metabolic heat production of germinating seeds may reflect the respiratory characteristics of seed and seedling vigor. This study was established to determine the feasibility of using calorimetric data as an index of seedling vigor. Soybean [Glycine max (L.) Merr.] seeds and a multiplex heat conduction calorimeter were used in this study. Calorimetric measurements of single seeds were conducted for 48 hours at 30 °C under dark. Seedling length and weight were measured immediately after the calorimetric measurement and after a 5-day incubation period. The total metabolic heat evolution from 12 to 48 hours was used for analysis. The total metabolic heat evolution curves during seed germination over a given time were exponential and were consistent with the exponential growth curves generally recognized for soybean seedlings at the early stages of growth. The heat evolution of germinating seeds was positively correlated with the length and fresh weight of 2-day old and 7-day old seedlings. These results suggest that total metabolic heat evolution during seed germination may be related to the potential for subsequent seedling growth and may be used to predict seedling vigor. Calorimetric data describing heat evolution of germinating seeds may be a useful tool for characterizing seedling vigor
Radiation interception and use in a maize and bean intercropping system
No full textEnglish: Food shortage is known to have been caused by overpopulation, natural disasters and poor food distribution. In areas facing food insecurity, such as Africa, peasants or smalIscale farmers have practised traditional cropping techniques since old times. One of the techniques is intercropping, and many intereropping studies have been reported since the 1960s. According to those studies, intereropping has higher productivity and also higher resource use than sole cropping, however, the contribution of crop radiation utilisation to that higher productivity is unclear. From this background, a quest as to whether intereropping was suitable to small-scale farming in a semi-arid region (Free State, South Africa) has started. The main aim of this study was to analyse and model radiation interception and employment in a maize-bean intereropping system with alternate (northsouth and east-west) row directions (Chapters 3 and 4). Also, the intererop yield advantage was assessed in terms of intensity of land use, accumulation of energy and return of cash increment (Chapter 2); and photosynthetically active radiation (PAR) above plant canopies was investigated (Chapter 5). In Chapter 2 it was shown that the maize-bean intereropping had a yield advantage, compared with the sole cropping, under the set conditions used for both maize and beans planting. In other words, maize-bean intereropping was equivalent in yield to sole maize, and gave a higher yield than sole beans. This was explained by crop radiation interception and use in Chapter 3. The intereropping was analogous to maize sole cropping in the overall efficiency of radiation interception and use, and had greater radiation interception and use than bean sole cropping. In addition, no difference in crop productivity and efficiency was found between row direction treatments. In the modelling study (Chapter 4), the intercropped maize had the same growth efficiency as the sole cropped maize, but beans had greater radiation utilisation in intereropping than in sole cropping. This resulted in an intereropping yield advantage. In Chapter 5, an empirical equation for estimating PAR from solar radiation has been introduced because PAR is not routinely measured at weather stations. The equation may be accurate enough to compute PAR from the large data sets available across southern Africa. This study has shown that planting maize in association with beans is advantageous compared with separate planting, in both crop productivity and efficiency. Normally, small-scale farmers cultivate not one crop but a staple crop and supplement crops. From this point of view, the conclusion is drawn that intereropping is suitable for use in the small-scale farming sector.Afrikaans: Dit is bekend dat oorbevolking, natuurrampe en gebrekkige voedselverspreiding
grotendeels die oorsaak van voedseltekorte is. In gebiede soos Afrika, waar
voedselonsekerheid die arm bevolking of kleinskaalboere dikwels in die gesig staar, is
boere goed vertroud met die tradisionele verbouingstegnieke van toeka se dae. Een van
die tegnieke is tussen- of kruisverbouing wat die studieveld al in die 1960s betree het.
Volgens bewese resultate lewer tussenverbouing hoër opbrengste en veral hoër
gewashulpbronverbruik as enkelverbouing. Na aanleiding van hierdie agtergrond is daar
gepoog om die gepastheid van kruisverbouing op kleinskaalboerdery in die semi-ariede
area (Bloemfontein, Vrystaat, Suid Afrika) na te vors en is 'n studie uitgevoer om
gewasstralingsonderskepping en verbruik van gewasstraling te ondersoek. Die hoofdoel
van die studie is die analise en modellering van stralingsonderskepping en verbruik in die
mielie/bone tussenverbouing met twee verskillende (noord-suid en oos-wes) ryrigtings
(Hoofstukke 3 en 4). Verder is die kruisverbouingsopbrengsvoordeel bereken in terme
van intensitiet van landsverbruik, akkumerlering van energie en geldverdienste (Hoofstuk
2) en is ondersoek ingestel na fotosintetiese aktiewe sraling (FAS), wat die primêre faktor'
is in plantegroei bokant plantgewasdakke (Hoofstuk 5).
In Hoofstuk 2 is bewys dat tussenverbouing 'n opbrengsvoordeel teenoor monoverbouing
toon, met die veronderstelling dat beide mielies en bone geplant word. Met ander woorde,
mielie-bone tussenverbouing is ekwivalent in opbrengs aan slegs mielies en toon 'n hoër
opbrengs as slegs bone. Hierdie verskynsel word deur gewasstralingsonderskepping en -
verbruik in Hoofstuk 3 behandel. Die tussenverbouing het ooreengekom met slegs
mielieverbouing in die algehele doeltreffendheid van stralingsonderskepping en verbruik
en wys hoër stralingsonderskepping en verbruik as die geval by slegs boneverbouing.
Verder, geen verskil is tussen ryrigting behandelings op opbrengste en doeltreffendheid
gevind nie. In Hoofstuk 4 (modelleringstudie) is gevind dat die tussenverboude mielies
dieselfde groeidoeltreffendheid as slegs verboude mielies het, maar dat bone groter
stralingsverbruik by tussenverbouing as by monoverbouing toon. Dit kan lei tot die
tussenverboude opbrengsvoordeel. In Hoofstuk 5 word 'n empiriese vergelyking vir
berekening van FAS vanaf straling voorgestel, omdat FAS nie normaalweg gemeet word
deur weerstasies nie. Die vergelyking mag akkuraat genoeg wees om FAS by groot
datastelle te bereken.
Hierdie studie het bewys dat die gesamentlike aanplanting van mielies en bone voordelig
is vir gewasproduktiwiteit en doeltreffendheid, in vergelyking met afsonderlike
aanplanting. Gewoonlik sal kleinboere nie 'n enkele gewas nie, maar 'n
hoofvoedselgewas plus supplementêre gewasse kweek. Die gevolgtrekking is dus gemaak
dat tussenverbouing gepas is vir kleinskaalboerdery
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
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