Typescript. / Thesis (Ph. D.)--University of Hawaii at Manoa, 1974. / Bibliography: leaves 322-332. / xvii, 332 leaves ill. (some col.), maps

Light availability in forest understories is a well recognized constraint on sapling growth, but limitations in soil nitrogen (N) availability, and the link to foliar photosynthetic capacity, typically receive less consideration in describing stand dynamics. My primary hypothesis is that light and soil N availability have species-specific effects on photosynthetic activity and growth, and that together these resources will better define understory development in complex forests. To test these relationships, I examined 1) soil N indices and the tradeoffs between soil fertility and light attenuation in old-growth forest understories; 2) the effects of light and N constraints on understory sapling foliar N concentration (N%), N per unit area (Na), and natural abundance of ¹³C; 3) the effects of light and soil N supply on species growth and photosynthetic activity in a factorial field experiment; and 4) the mechanisms responsible for the stagnation of understory saplings. Soil N indices incorporating dissolved inorganic N and organic N were useful in characterizing differences in N supply among contrasting sites. Understory light availability declined with increasing soil N supply, while understory Abies lasiocarpa had strong correlations between foliar N% and soil N availability, despite shading effects. In partial-cut forests, understory Tsuga heterophylla and Picea glauca x sitchensis had consistent foliar N% across gradients of light availability; in contrast, foliar N% of Betula papyrifera and Thuja plicata declined with increasing shade, which would distort assessments of soil fertility and perhaps contribute to increased mortality of these species in deep shade. Strong correlations between foliar Na and ¹³C or growth increment suggest foliar N per unit area is the simplest integration of light availability and N nutrition on leaf photosynthetic activity. Ontogenic interactions that occur among foliar attributes and tree size in forest understories, especially for saplings < 1 m in height, contribute to time effects on growth patterns and emphasize the need for long-term studies of species autecology and stand dynamics. My experimental manipulation of light and N supply on saplings was ineffective, and future research using natural gradients in site productivity may be more fruitful in defining species response to light and N interactions.

Diss. (sammanfattning) Uppsala : Sveriges lantbruksuniversitet, 2006. / Härtill 4 uppsatser.

Thesis (Ph. D.?)--Universitat Bayreuth, 2006.

Thesis (Ph. D.)--University of Missouri-Columbia, 2004. / Typescript. Vita. Includes bibliographical references (leaves 75-81). Also available on the Internet.

Thesis (Ph. D.)--University of Missouri-Columbia, 2004. / Typescript. Vita. Includes bibliographical references (leaves 75-81). Also available on the Internet.

Thesis (Ph.D.)(Agricultural Economics)--University of Pretoria, 2007. / Includes summary. Includes bibliographical references. Available on the Internet via the World Wide Web.

Thesis (MScFor (Forest and Wood Science))--Stellenbosch University, 2008. / This study sought to examine the effects of soil fertility replenishment (SFR) adoption on household security and poverty reduction in smallholder farming households of central and southern Malawi by assessing food security, asset status, and household income generating activities in Kasungu and Machinga Districts during 2007. The results showed that households had been able to significantly increase maize production by an extra 382 kg per year in Kasungu and 242 kg per year in Machinga Districts, which constitutes approximately 35% and 22% of average household maize requirements for the year for each district, respectively. This reduced the critical annual hunger periods from 3.46 months to 2.80 months per year in Kasungu and from 4.31 months to 3.75 months in Machinga. Respondents also reported a significant increase in assets and an increase in income. Despite these positive changes, households were found to still be living in extreme poverty. Selling physical assets was the most common response to shocks and any increase in income was allocated to the purchase of food, household supplies, and other items necessary to immediate survival. This study revealed that while food security is paramount to the sustainable livelihoods of smallholder farmers, livelihood security and poverty reduction depend on more than increased food production. SFR technologies are fulfilling their primary role as a means to food security, but their adoption does not lead to significant livelihood improvements. Achieving lasting impacts requires that initiatives take an integrated approach and address not only household food production, but the multifaceted dynamics of social institutions, markets/economy, and policy. The long-term impacts of the current agroforestry programs in the study areas will emerge only with time. Livelihood improvements will depend on several factors. First, market inefficiencies must be remedied and economic barriers must be broken down. Second, the challenges identified by the respondents, especially access to resources and training, need to be addressed in a participatory way that promotes education and empowerment. As these two issues are tackled, households will become better equipped to manage the complexities that arise from SFR adoption and livelihood diversification. It is recommended that future research and initiatives should focus on identifying and removing economic barriers to markets, addressing farmeridentified challenges such as access to seed, water, and education and training, supporting households in managing multiple livelihood strategies, and continuing research to identify appropriate agroforestry species and technologies.

Indigenous agroforestry systems, or the intentional use of trees and livestock in croplands, have a long history in the West African Sahel. In many locations, they have long contributed to food security and climate change resilience. But a century or more of cash cropping and use of modern agricultural inputs and tools has meant that no such agroforestry systems remain intact, and many are extinct, including in west-central Senegal, where the Serer historic mixed farming and pastoral strategies previously provided resilience to cyclical droughts and colonial-era agricultural and economic change but are now neither intact nor extinct. This study examines the current state of Serer agroecosystems, considering who uses what elements of the old systems, who has introduced what elements of nonindigenous farming systems, and whether this combination of local and imported farming systems is a coherent and sustainable fusion, or an incoherent pastiche leading toward agrarian collapse. I argue that, depending on how farmers integrate new models with the technical and cultural elements of the old system, a coherent fusion may result, with positive implications for sustainability, climate change adaptation, soil replenishment, crop yield, and livelihood resilience. This mixed-methods study draws upon literature from cultural ecology, agroecology, socioecological resilience, and history to interpret farmers’ accounts of changing agrarian practices. The study links ethnographic findings to empirical analysis of soil conditions and land use change. With these tools, my research sheds new light on the evolving role of local techniques and knowledge in the struggle to maintain agricultural productivity, as Sahelian communities confront soil fertility depletion, food insecurity, and climate change. The study finds that farming communities in this region can strengthen their livelihood resilience and enhance crop yields if they update elements of the well-adapted historic farming system, employ new techniques and tools, and in the process, forge coherent farming systems that still make cultural sense to farmers. / 10000-01-01

Made available in DSpace on 2014-06-11T19:31:33Z (GMT). No. of bitstreams: 0 Previous issue date: 2010-01-29Bitstream added on 2014-06-13T18:42:19Z : No. of bitstreams: 1 morales_mm_dr_botfca.pdf: 985827 bytes, checksum: c47574acdcc4d6b770e1055c47ca76c4 (MD5) / Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Suprir a demanda de alimento para mais de 6 bilhões de pessoas promovendo agricultura de forma sustentável é o desafio do novo milênio. O biocarvão (BC), ingrediente que proporciona ao solo capacidade de reter matéria orgânica e nutrientes, pode ser uma ferramenta de grande importância na busca de soluções para esse desafio. Portanto, entender o efeito do BC sobre o comportamento da matéria orgânica (MO) e o ciclo do fósforo inorgânico (Pi) em solo degradado foram os objetivos deste trabalho. A taxa de mineralização e o teor de carbono total foram monitorados nas misturas de solo degradado + 35%BC + doses de MO iguais a 0, 10, 40, 70 e 100 t ha-1, nos tempos 0, 80, 160, 240 e 320 dias de incubação em estufa. Reações de sorção e dessorção de Pi foram avaliadas nas misturas de solo degradado + 35%BC + doses de P com 0, 75, 150, 200 e 300 mg kg-1, no tempo 240 dias de incubação, além do controle com somente solo, para ambos os estudos. A adição de BC ao solo promoveu a mineralização da mistura; entretanto, o BC apresentou tendência à recalcitrância ao longo do período, dobrou o tempo de reação com o P tanto para as reações de sorção quanto dessorção, diminuiu a sorção de P do solo e dessorveu quantidades ideais para a maioria das culturas. O BC possui poder fertilizante, porém sua utilização deve ser assistida por possuir características químicas limitantes como pH e sais. Palavras chave: Fertilidade do solo, sorção, dessorção, mineralização. / To supply the food demand for more than 6 billion people, promoting sustainable agriculture is the chellenge for the new milennium; the biochar (BC) ingredient that provides the ability to retain soil organic matter and nutrients can be an important tool to figure oout solutions for this challenge, thus, understand the effect of BC on the organic matter (OM) behavior and at inorganic phosphorus (Pi) cycle in degraded tropical soil has been our goal. The mineralization rate and total carbon content were monitored in mixtures of degraded tropical soil + 35% BC + OM doses, equal to 0, 10, 40, 70 and 100 t ha-1 at 0, 80, 160, 240, and 320 greenhouse incubation days. Pi Sorption and desorption Reactions were analysed in mixtures of degraded tropical soil + 35% BC + P rates of 0, 75, 150, 200, 300 mg kg-1, on 240 days of greenhouse incubation, beyond the control with soil by itself. The BC soil addition promote mineralization, however presented recalcitrance tendency in the incubation time, doubled the time of reaction with P for both the reactions of sorption and desorption, decreased P sorption and desorption of soil quantities ideal for most crops. The BC can act as a fertilizer, but its dosage should be well attended as it has the capacity to increase soil pH and salt.