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Crop rotation is one of the pillars of conservation agriculture (CA). It has been adopted moderately in the summer rainfall area of South Africa, but the adoption of conservation tillage has been very slow. It has been observed that research information on crop rotation helped with the adoption of the CA concept in the Western Cape. Limited research has been done on crop rotation in the Eastern Free State. This study used the crop matrix trial design to evaluate the impact of different cropping sequences in a CA system on the growth, development, yield and quality of wheat as target crop. The profitability and production risk of the different crop rotations were also determined. Only preceding summer crop sequences had a significant (Pâ¤0.1) influence on the yield parameters of the final wheat crop. For the final wheat crop three preceding sequences, namely sorghum à soybean, maize à sunflower and soybean à maize, led to a lower (Pâ¤0.1) number of plants and ears, with a lower biomass and residue yield unit area. Although the poorest response was always recorded on the preceding sorghum à soybean sequence plots, it did not differ significantly from those of the other two crop sequences. The final wheat crop also had a significantly higher TKM and harvest index on preceding sorghum à soybean sequence plots. It was concluded that the lower number of plants on these plots could be attributed to lesser in-row competition for water and nutrients, which resulted in bigger and heavier wheat kernels with a higher TKM. The study confirmed previous research, namely that the final wheat crop planted on second season sunflower plots had a significantly (Pâ¤0.1) higher number of ears m-2, with a better N(grain) use efficiency. That resulted in a significantly higher grain protein content. However, the yield of the final wheat crop did not differ between plantings on second season summer crop plots. Rotation with oats is often recommended to reduce Take-all, a soil-borne disease of wheat. It was found that the final wheat crop planted on second season oats plots had a significantly lower seedling number, with fewer ears and a lower grain yield per unit area. The wheat plants also had a lower (Pâ¤0.1) precipitation use efficiency and grain nitrogen use efficiency, which led to a lower accumulation of grain protein. It was concluded that oats has a negative influence on wheat yield in a rotation system and that the crop should only be used as a break crop against Take-all. Thirty two of the 50 crop rotations had a total profit margin above the chosen target income of R1,000 ha-1. The soybean à maize à wheat rotation gave the highest total profit of R7,549.76 ha-1, while the sorghum à dry bean à wheat rotation realised the highest total loss of R1,903.93. Maize had a stable yield over two seasons, while the yield of the other four preceding summer crops posed a higher production risk under rainy conditions (pod shattering in dry bean and soybean crops), or potential bird damage situations (sunflower and sorghum). The crop matrix technique proved to be a reliable method to generate more information on cropping sequence in the same trial over a much shorter period. A multi-disciplinary approach in future cropping sequence research will help to provide producers with reliable information. If crop sequences can be proven to be effective at research level, clear guidelines and recommendations can be developed to help producers in implementing conservation tillage more successfully in the Eastern Free State.

Maize (Zea mays L.) is an important cereal crop not only in the world but more specifically in South Africa. Therefore, understanding maizeâs nutrient requirement becomes an importance factor especially during the vegetative growth period. Nitrogen (N) and phosphorus (P) are reported to be two essential nutrients for both accelerated vegetative growth and maximum yield. Addition of these two plant nutrients should include consideration of both form and total nutrient concentration, since these two factors determine availability and accessibility. In order to evaluate the response of maize to P sources and P application rates as well as N sources a glasshouse experiment was conducted in 40.5 L pots filled with a dark brown sandy-loam topsoil pertaining a medium soil pH of 5.5. Treatments consisted of three main factor treatments viz. N source (urea and limestone ammonium nitrate - LAN), P source (monoammonium phosphate - MAP, nitrophosphate - NP and ammonium polyphosphate - APP) and P application rate (0, 10, 20, 30 and 40 kg P ha-1). Treatments combinations were replicated three times and independently subjected to a randomized complete block design with a factorial combination. The experiment was repeated on two planting dates. Treatments and treatment combinations were band applied to dry soil in a single 0.34 m line, 50 mm below and 50 mm away from the maize seeds; which were planted with a between row spacing of 0.91 m, 50 mm below the soil surface. After planting the soil was watered and maintained at field capacity for a duration of five weeks after emergence. The aerial parameters of three plants per pot were measured on a weekly basis following emergence while the subsoil parameters were taken at the end of the five week vegetative growing period. Both aerial and subsoil parameters showed responses to nitrogen source; which was strongly reflected during both plantings. Plants treated with LAN yielded both greater aerial and subsoil measurements compared to urea, primarily ascribed to immediate availability after application in addition to ease in uptake. Both aerial and subsoil parameter response to phosphorus source and P application rate, though apparent throughout both plantings, was more prominent during the first planting. Monoammonium phosphate and NP (orthophosphate sources) yielded greater aerial measurements compared to that of the APP (polyphosphate source). Subsoil parameter results comparing phosphorus sources were inconsistent. Subsoil parameters of the fertilized zone were significantly greater with the use of MAP (orthophosphate), while APP (polyphosphate) yielded significant greater subsoil parameters within the unfertilized zone. Both aerial and subsoil parameter measurements taken either throughout or at the end of the vegetative growth period were overall significantly greater when P was applied at 40 kg P ha-1. Subsoil parameter response in and away from the fertilizer band was however inconsistent. The aerial dry plant material was analyzed (Omnia Nutriology®) to evaluate the effect of the three main treatments on the quantitative nutrient concentration as well as the uptake thereof. Nutrient concentration and uptake was used to determine the synergistic or antagonistic effect of treatments or treatment combinations. Nutrient concentration measurements were inconsistent for N source, however total uptake proved to be more efficient with the application of LAN compared to urea. Both nutrient concentration and uptake was greater with the application of both the orthophosphate sources (MAP and NP) compared to the polyphosphate source (APP). The 40 kg P ha-1 application yielded a synergistic response to the total uptake of S, N, P, Ca and B, while a synergistic nutrient concentration response was found with the control treatment for N, Mg, Cu and Zn nutrients. Nutrient uptake was also stimulated by an increasing rate of P.

Over the past decades, we have seen escalating costs associated with the direct socioeconomic impacts of hydrometeorological events and climate extremes such as flooding, rising sea levels due to climate change, solid earth changes, and other anthropogenic activities. With the increasing population in the era of changing climate, the number of people suffering from exposure to extreme events and sea level rise is expected to increase over the years. To develop resilience plans and mitigation strategies, hindcast exposure models, and calculate the insurance payouts, accurate maps of flooding extent and socioeconomic exposure at management-relevant resolution (102m) are needed. The growing number and continually improving coverage of Earth-observing satellites, an extensive archive of big data, and machine learning approaches have transformed the community's capacity to timely respond to flooding and water security concerns. However, in the case of flood extent mapping, most flood mapping algorithms estimate flood extent in the form of a binary map and do not provide any information on the uncertainty associated with the pixel class. Additionally, in the case of coastal inundation from sea level rise, most future projections of sea-level rise lack an accurate estimate of vertical land motion and pose a significant challenge to flood risk management plans. In this dissertation, I explore an extensive archive of available remotely sensed space-borne. synthetic aperture radar (SAR) and interferometric SAR measurements for 1) Large-scale flood extent mapping and exposure utilizing machine learning approaches and Bayesian framework to obtain probabilistic flood maps for the 2019 flood of Iran and 2018 flood of India and 2) Assessment of relative sea-level rise flooding for coastal disaster resilience in the Chesapeake Bay. Lastly, I investigate how climate change affects hydrology and cryosphere to 3) understand cryosphere-climate interaction for hazard risk and water resources management. / Doctor of Philosophy / Flooding increased exponentially in recent decades due to changes in climate and human activities. With an increasing number of people and flooding events, exposure to such events has been enhanced. The presence of satellites in space, the increase in revisit-time, and better tools and techniques to map flood extents have transformed society's ability to respond to hazard and water-related issues. To develop risk management plans and project how many people will be affected by hazards, and calculate the insurance payouts, accurate maps of flooding extent, and socioeconomic exposure at management-relevant resolution are needed. However, in terms of flood mapping, most flood maps do not provide information on how much water is there on a particular map. In addition, in the case of coastal flooding coming from sea level changes, current methods for future scenarios of flooding, do not accurately account for how the ocean is rising with respect to the land-encompassing movement of the land. This causes a significant challenge to coastal flood risk management plans. Therefore, in this dissertation, I explore large datasets from satellites for 1) Accurate flood extent mapping and 2) Estimation of coastal flood from relative sea level rise. Lastly, I also, examine how climate change is affecting ice and water changes to 3) Understand the role of climate on the water for hazard risk and water management.

Proposant une approche méthodologique fondée sur la sémiologie des indices et la sémiotique narrative, notre travail doctoral sous convention CIFRE pour EDF R&D s’attache à comprendre le fonctionnement structural et narratif des représentations du changement climatique dans différentes sphères sociales en France. Partant du caractère scientifique de l’Objet de recherche, l’étude s’intéresse aux discours forgés par les climatologues, la presse de vulgarisation scientifique, trois titres de la presse quotidienne nationale et les discours profanes au travers d’entretiens collectifs, selon une temporalité commune, de novembre 2009 à mars 2010. La « Une » des quotidiens et des magazines de vulgarisation scientifique est alors considérée comme un marqueur social et historique fort, capable de construire les représentations relatives au changement climatique. Le corpus de presse d’information fonde les représentations tant du phénomène climatique que des événements médiatiques qui lui donnent une existence. Le recours à la sémiotique narrative permet une comparaison de corpus de natures différentes, afin de prendre la mesure de la circulation entre les différentes sphères sociales visitées. L’objectif étant une compréhension globale des représentations climatiques, permettant une réflexion sur les mythes dont nos sociétés se nourrissent pour se construire, et sur le possible ré-enchantement de ces mythes. / This doctoral research, conducted through a CIFRE agreement with EDF R&D, aims to understand the structural and narrative organization of climate change representations through four different social spheres in France. First considered as a scientific topic, climate change representations are analysed throughout climate scientists and profane discourses, but also throughout documents such as science popularization magazines and three French newspapers, which of the front pages are considered as a social and historical tracer, particularly during the period running from November 2009 to March 2010. Informative press corpus enables to construct representations of global warming and of the media events that participate to their media life. The use of narrative semiotic methodology allows a comparative study through the different corpuses, in order to spot out the hypothetical circulation of these representations. The eventual aim is a global understanding of climate representations, opening the way for a consideration of the different myths as a basement of our societies, willing to reinvent themselves through new social and cultural myths.