Thesis (M.S.)--Mississippi State University. Department of Plant and Soil Sciences. / Title from title screen. Includes bibliographical references.

Eastern North Dakota has received excessive rainfall events since 1995, and soils are prone to waterlogging. This research evaluated the effects of subsurface tile drainage, raised beds, and iron-chelate (Fe-EDDHA) seed-application on iron-deficiency chlorosis (IDC) incidence in soybean [Glycine max (L.) Merr.], soybean growth, and yield, across six environments during 2013 and 2014. Tile drainage without beds increased soybean yield and reduced IDC by 11%. Beds resulted in more vigorous plants with 9% more biomass and increased soybean yield by 6%. There was no yield advantage to using both tile and raised beds within the same field. The Fe-EDDHA reduced plant population and IDC expression, increased plant biomass, but did not result in a yield increase. Farmers are encouraged to consider utilizing raised beds as a means to mitigate excess water. Additional research is needed to determine the cause of lower established plant density after seed application with Fe-EDDHA. / Minnesota Soybean Research and Promotion Council / North Dakota Soybean Council / DuPont Pioneer

L'Amazonie a connu une longue histoire d'occupation humaine. La nature et l'échelle de l'impact des populations d'Amérindiens précolombiens sur leur environnement sont encore largement débattues. Dans une approche pluridisciplinaire, la thèse vise 1) à améliorer les estimations de l'étendue des remaniements anciens des paysages par l'Homme et 2) à comprendre comment ces remaniements affectent la structure et le fonctionnement des écosystèmes contemporains par l'étude des complexes de champs surélevés précolombiens des savanes côtières de Guyane française. Pour la mise en place d'une agriculture intensive sédentaire, les agriculteurs précolombiens ont transformé ces savanes saisonnièrement inondées en édifiant des champs sous la forme de buttes de terre circulaires produisant une hétérogénéité topographique marquée et organisée. Pour répondre au premier objectif, nous avons développé deux approches permettant de distinguer les paysages de buttes d'origine anthropique de ceux, dont la physionomie est très proche, résultant de processus naturels. Pour répondre au second objectif, nous avons décrit comment la structure des communautés d'ingénieurs naturels d'écosystèmes (fourmis, termites, vers de terre et plantes) répond à l'hétérogénéité induite par l'Homme, et comment les activités de ces ingénieurs assurent l'auto-entretien des anciens champs contre l'érosion depuis leur abandon il y a environ 800 ans. Notre travail révèle que l'étude de la dynamique temporelle de la végétation permet d'inférer l'origine des complexes de buttes uniquement lorsqu'elle combine différents proxys. L'analyse de la structure spatiale des buttes montre que les complexes de buttes de Guyane présentent une orientation souvent en grille carrée, orientation qui n'a jamais été montrée ni prédite pour des paysages d'origine naturel, indiquant que la géométrie du paysage peut porter la signature de l'intervention de l'Homme. Depuis l'abandon des champs surélevés, les communautés d'ingénieurs naturels se structurent, et concentrent leurs activités, dans les buttes. Nous avons montré que ces activités contribuent à maintenir des habitats surélevés contre l'érosion mais que les rétroactions qu'ils conduisent sur le sol sont modulées par les conditions initiales du milieu. Le paysage observé actuellement dans les savanes de Guyane n'est ni entièrement façonné par l'Homme, ni entièrement naturel mais résulte de l'interaction complexe entre les composantes physiques et biotiques et de l'héritage des activités anciennes de l'Homme. Le résultat de ces interactions est reflété par une mosaïque de buttes plus ou moins érodées. Notre travail représente la première étude montrant l'impact à long terme des activités anciennes de l'Homme sur les écosystèmes de savanes en Amazonie. Nos résultats présentent des applications importantes dans le domaine de l'ingénierie écologique pour la conception de nouveaux agroécosystèmes durables. / Amazonia has a long history of human occupation. The nature and scale of the impact of pre-Columbian humans on their environment are still hotly debated. In a pluridisciplinary approach, this thesis aims 1) to improve estimations of the scale of ancient landscape transformations by humans and 2) to understand how these transformations influence the structure and the functioning of contemporary ecosystems, by studying the particular exemple of pre-Columbian raised-field complexes in coastal savannas of French Guiana. To conduct sedentary intensive agriculture, pre-Columbian farmers transformed these seasonally flooded savannas by building raised fieldsin the form of circular moundscreating a marked and organized topographic heterogeneity. To accomplish the first objective, we developed two approaches to distinguish anthropogenic mound-field landscapes from others, of similar physiognomy, resulting from natural processes. To accomplish the second objective, we described how the structure of the community of natural ecosystem engineers (ants, termites, earthworms and plants) is influenced by human-induced heterogeneity, and how feedbacks generated by these engineers can lead to self-organized maintenance of the ancient fields against erosion since their abandonment around 800 years ago. Our work reveals that the study of the temporal dynamics of vegetation can be used to infer the origin of mound complexes only when it combines different proxies. The analysis of spatial structure of mounds shows that mound complexes of Guiana are strongly oriented, often in a square lattice, an orientation that has been neither demonstrated nor predicted for natural landscapes, indicating that landscape geometry bears a diagnostic signature of human activities. Ever since raised fields were abandoned, the community of natural engineers is structured, and its activities are concentrated, on mounds. We showed that these activities cont ribute to maintaining these raised features against erosion, but that the effectiveness of engineer-feedbacks on soil in countering erosion are modulated by initial conditions of the environment. The current landscapes of French Guianan savannas are neither solely modeled by humans nor entirely natural, but result from the complex interaction between physical and biotic components and from the legacies of past human land use. The result of these interactions is reflected in a mosaic of more or less eroded mounds. Our work represents the first study showing the long-term impact of ancient human activities on Amazonian savanna ecosystems. Our results can have important applications in the framework of ecological engineering to conceptualize new durable agroecosystems.

Modern agricultural systems have been criticized for their detrimental effects on the environment and a general emphasis on crop yield rather than long-term sustainability. Traditional forms of agriculture may provide case-specific examples of sustainable alternatives for contemporary societies. In the seasonally inundated savannas of the Llanos de Mojos, pre-Columbian Indians piled earth into ‘large raised field platforms’ elevated high enough above the floodplain to allow crops to grow. Archaeological evidence indicates that raised field agriculture supported much larger populations than those found in the Beni today. The examination of satellite imagery has revealed more than 40,000 individual fields spread across an area of approximately 7,500 square kilometers. This study created a digitized map of large raised fields to search for spatial patterns in their distribution. A GIS analysis was conducted in which fields were distributed into organizational groups based on characteristics such as proximity and orientation to cardinal direction. These groups represent potential ‘social units’ involved in the organization of labor required to construct raised fields. This study demonstrated the consistent presence of these units throughout the entirety of the agricultural system. Patterns in the distribution of these groups allowed the study area to be divided into two distinct regions representing a larger scale of organization within a seemingly uniform system. A transitional zone between these two regions was identified on the river Omi, providing a clear area of interest to target in future archaeological excavations. Further archaeological investigations of raised field agriculture have the potential of demonstrating the overall productivity of the system as well as how it was incorporated into the social systems of those who managed it.