This dissertation is composed of two manuscripts in Production Economics and two manuscripts in International Agricultural Development. The first two manuscripts focus on production economics, and both are an exploration of nitrogen use and its impact on continuous corn production and profitability in Colorado. The first manuscript titled "Switching Regression Stochastic Plateau Production Functions––A Comparison of Alternative Specifications" proposes an alternative approach for estimating crop yield response functions using a frequentist approach. The second manuscript titled "Profitability Effects of Different Tillage Systems in Continuous Corn Rotations" explores the interaction between different tillage systems and nitrogen fertilization in irrigated continuous corn production in northeastern Colorado. We find that strip tillage is better suited for continuous corn production under the agro-climatic conditions in northeastern Colorado. The third and fourth manuscripts focus on international agricultural development and analyze the role of factors that influence the agricultural development of small-holder farmers in Ecuador, namely, markets, food value chains, risk preferences, and risk perceptions. The third manuscript titled "Does the Use of Specialty Varieties and Post-Harvest Practices Benefit Farmers? Cocoa Value Chains in Ecuador" analyzes the impact of the use of specialty cocoa varieties on small-scale farmers' income. It finds that the use of specialty cocoa varieties has a low impact on small-scale cocoa producers' income, and that post-harvest practices may lead to substantial price responses irrespective of the type of cocoa grown. Finally, the fourth manuscript titled "Linking Risk Preferences and Risk Perceptions of Climate Change Using Prospect Theory" explores how farmers' risk preferences correlate with their perceptions of climate risk. It finds that farmers that behave in accordance to the assumptions of prospect theory are more likely to perceive greater risks from climate change, that is, they are more likely to perceive the risks associated with climate change as being more threatening at a personal level. Since risk perception is a necessary prerequisite for adaptation, the results presented in this manuscript, have important policy implications for process of adoption of new technologies aimed at mitigating effects of climate change. / Doctor of Philosophy / This dissertation focuses on Production Economics and International Agricultural Development. The first two manuscripts focus on production economics, and both are an exploration of nitrogen use and its impact on continuous corn production and profitability in Colorado. The first manuscript proposes an alternative approach for estimating crop yield response functions to a single input. The second manuscript explores the interaction between different tillage practices and nitrogen fertilization in irrigated continuous corn production. The third and fourth manuscripts focus on international agricultural development, and they analyze the role of different factors that influence the agricultural development of small-holder farmers in Ecuador. The third manuscript analyzes cocoa markets in Ecuador. It finds that the use of gourmet cocoa varieties has a low impact on small-scale cocoa producers' income, and that post-harvest practices may lead to substantial benefits. Finally, the fourth manuscript explores farmers' risk behavior. It finds that farmers that behave in accordance to the assumptions of prospect theory, are more likely to show a greater risk perception of climate change, that is, they are more likely to perceive the risks associated with climate change as being more threatening at a personal level. Since risk perception is a necessary prerequisite for adaptation, the results presented in this manuscript, have important policy implications for the adoption process of new technologies aimed at mitigating effects of climate change.

Broccoli is increasingly being grown as an alternate crop in many tobacco producing regions. Many of these regions, especially in Virginia, are quite susceptible to soil erosion losses. In order to reduce erosion and reap the other benefits of conservation tillage, a strip tillage machine named FOR2 was designed, developed and tested. FOR2 prepares the seedbed and places the seed in one pass through the field. This thesis reports the qualitative and quantitative evaluation of FOR2 based on result from two experiments. The first experiment evaluated broccoli emergence under three different tillage treatments, one of which was FOR2. The second experiment assessed the influence of adjustable machine parameters on the prepared soil condition in terms of aggregate size distributions, The parameters that were varied included pre-planting irrigation amount, tiller depth, tiller RPM, and tractor speed. The analysis revealed that the FOR2 machine produced commercially acceptable stands of broccoli with 77% germination. It was also determined that the percentage of aggregates in the seedbed greater than 0.297 mm was significantly influenced by the irrigation level and the tiller RPM. Tiller depth and tractor speed had no significant effect on the response. / M.S.

Comparing farms using different corn tillage methods, farms using reduced corn tillage had higher returns to fixed resources than farms using conventional corn tillage in all cases, except when energy prices were increased by 50, 75, and 100 percent. At these higher energy price increases, since conventional corn tillage had lower energy costs per unit of feed produced, conventional corn tillage was more profitable. Quantities and costs of energy used to produce the feed for the cow herd were directly related to what crops were produced and what quantities of feed were purchased. Farms using reduced corn tillage were consistently the higher energy users compared with farms using conventional corn tillage, except when 75 and 100 percent energy price increases occurred; but this result might have been different if energy used to produce the purchased feed had been considered. Reductions in returns to fixed resources, when energy quantities are restricted, are much more severe than reductions in returns to fixed resources with energy price increases.l1 This result indicates that if government were faced w~th the choice of an energy conservation policy based on large energy price increases, or an energy conservation policy based on a strict rationing of energy inputs, the strict rationing policy would probably cause greater reductions in livestock farmer's income. / Master of Science

Cabbage (<i>Brassica oleracea</i> L.) production in Virginia is concentrated in the mountainous southwest region of the state where soil erosion and soil-moisture deficits are major problems associated with row-crop agriculture. The objectives of this study were to assess the applicability of conservation tillage systems for cabbage production. Four tillage systems (conventional tillage, CT; no-tillage, NT; and two types of strip tillage—Ro-till, RT, and chisel plow, CP) and three planting dates (early, mid and late) were compared in 1985 and 1986. Plants were set with a locally adapted no-till transplanter into a cover crop of cereal rye (<i>Secale cereale</i> L.). Under unusually rainy conditions in 1985, cabbage yields with NT were lower than with CT; while with dry weather prevailing in 1986, NT and CT yields were equal for all planting dates. Yields in strip tillage systems were equal or higher than NT and CT with ample or deficit soil moisture. RT out-yielded both CT and NT in 1986. Yield was positively correlated with soil moisture content in 1986, but not in 1985. Once-over resetting was done in all plots resulting in no differences in plant numbers among tillage treatments. Head size was affected by tillage systems and was highly correlated with yield. These data indicate that (i) conservation tillage systems are viable alternatives to CT for production of cabbage, and (ii) available water resources and soil drainage should be important considerations in selection of the most productive tillage system. / M.S.

Masters of Science / Department of Agricultural Economics / Hikaru H. Peterson / Concerns about environmental degradation due to agriculture have gained importance as it is associated with soil erosion, health hazards, and ground water pollution. Environment-friendly land use practices have been developed to gain a wide range of environmental benefits including reduced soil erosion, reduced nutrient runoff from crop and livestock facilities, increased biodiversity preservation efforts, and restoration of wetlands and other native ecosystems. No-till is one such practice where soil erosion, nutrient runoff and environmental degradation can be reduced to a certain extent. This study evaluated the factors affecting the adoption of tillage systems in Kansas. A survey was conducted with a total of 135 participants from four different locations in the state of Kansas between August 2006 and January 2007. The adoption process was modeled as a two-step econometric models consisting of perception and adoption equations to estimate the impacts of demographic variables and farmers’ familiarity with and participation in certain conservation programs. The results for the perception models showed that the farm operators’ perceptions regarding whether BPM installation and management is unfair to producers or not and whether environmental legislation is often unfair to producers do not vary systematically across farm size, producers’ familiarity and participation in conservation programs, or other demographics considered in the study. On the other hand, their perceptions regarding how polluted their water supplies varied by their thoughts on relative profitability across various tillage practices, their primary occupation, and their familiarity with conservation programs. Specifically, the results suggested that those who regarded no-till practices to be more profitable than other tillage practices or whose primary occupation was farming-related tended to believe that ground water was not polluted, and those who were less familiar with available conservation programs tended to believe that surface waters were not polluted. The adoption model results suggested that farmers with greater operating acreage, those who perceived that no-till was more profitable than other tillage systems, and those with greater familiarity with and participation in existing conservation programs were more likely to adopt more conservation tillage systems, all else equal. Further, perceptions of fairness of environmental regulations or the level of pollution did not impact the tillage choices.

O sistema de manejo adotado e o tempo de cultivo acabam influenciando na disponibilidade de nutrientes, promovendo mudanças nas formas com que estes nutrientes se acumulam no solo, principalmente no caso do fósforo. Objetivou-se com o estudo avaliar as mudanças em longo prazo promovidas por sistemas de manejo do solo na fertilidade e nas frações de P em solos de Cerrado. Visando a melhor caracterização do bioma, foram analisados quatro experimentos de manejo do solo instalados em quatro locais representativos do Cerrado, sob Latossolo Vermelho (LV) ou Latossolo Vermelho-Amarelo (LVA), localizados em Costa Rica-MS (LV-1), Sapezal-MT (LV-2), Luziânia-GO (LVA-1) e Tasso Fragoso-MA (LVA-2). O delineamento experimental foi em blocos ao acaso, com parcelas subdividas, com parcelas constituídas pelos manejos, sendo eles o plantio direto (PD), o preparo convencional (PC) e a vegetação nativa (Cerrado), e como subparcelas foram consideradas as profundidades avaliadas: 0-5, 5-10 e 10-20 cm, com quatro repetições, totalizando 36 parcelas por área de estudo. Analisaram-se os atributos químicos do solo: potássio (K), cálcio (Ca) e magnésio (Mg) trocáveis, matéria orgânica (MO), acidez potencial (H + Al), e ainda a saturação por cátions no solo (V%). Realizou-se também o fracionamento do P visando identificar frações inorgânicas e orgânicas no solo. Os extratores, na sequência, foram: resina (PRTA), NaHCO3 0,5 mol L-1 (PiBIC e PoBIC), NaOH 0,1 mol L-1 (PiHID-0,1 e PoHID-0,1), HCl 1 mol L-1 (PHCl), NaOH 0,5 mol L-1 (PiHid-0,5 e PoHid-0,5) e a digestão do resíduo (PResidual, Pi e Po). A MO do solo foi influenciada diretamente pelo sistema de manejo, com aumento expressivo na camada superficial (0-5 cm) do solo quando manejado sob PD e com maior tempo no sistema. O pH, a acidez potencial e os teores trocáveis de K, Ca e Mg, bem como a saturação por bases do solo, em superfície (0-10 cm), foram maiores com a adoção do PD, comparado ao PC, em função deste manejo promover a deposição em superfície de corretivos, fertilizantes e resíduos vegetais no solo, o que não ocorre no PC. A adoção do PD resultou em acúmulo de frações orgânicas de P na camada superficial do solo e incrementou todas as frações inorgânicas de P, com maiores diferenças para o PC nos 10 primeiros cm do solo. O PC promoveu acúmulo de frações orgânicas de menor labilidade em subsuperfície nos solos argilosos. No solo mais arenoso a proporção das frações orgânicas de P foi muito inferior à observada em solos argilosos. / The soil management and cultivation time affect the availability of nutrients, changing the forms that they accumulate in the soil, especially in the case of phosphorus (P). This study aimed to evaluate the changes promoted by long-term tillage systems on soil fertility and on P fractions in Cerrado soils. To the better characterization of the biome, four experiments of soil management were analyzed, in four sites representing the Cerrado under Brazilian Oxisols (\"Latossolo Vermelho\", LV and \"Latossolo Vermelho-amarelo\", LVA) , located in Costa Rica - MS (LV-1) , Sapezal - MT (LV-2), Luziânia - GO (LVA-1) and Tasso Fragoso MA - (LVA-2). The experiments were distributed in a split plot randomized blocks design, with plots constituted of managements no-till (PD), conventional tillage (PC) and native vegetation (Cerrado), and the depths of 0-5, 5-10 and 10-20 cm were considered as subplots, with four replications, totaling 36 plots per study area. The soil chemical attributes analyzed were: exchangeable potassium (K), calcium (Ca) and magnesium (Mg), organic matter (MO), potential acidity (H+Al) and soil cations saturation (V%). Also, the fractionation of P was analyzed to identify organic and inorganic P fractions, using the following extractors: resin (PRTA), NaHCO3 0.5 mol L-1 (PiBIC and PoBIC), NaOH 0.1 mol L-1 ( PiHID-0,1 and PoHID-0,1), HCl 1 mol L-1 (PHCL), NaOH 0.5 mol L-1 (PiHID-0,5 and PoHID-0,5) and residual P digestion (PResidual). The soil OM was directly affected by management systems, with expressive increase in the soil surface layer (0-5 cm) when managed under PD and longer time. The pH, potential acidity and levels of exchangeable K, Ca, Mg, and V% in soil surface (0-5 and 5-10 cm) were higher with PD compared to PC, because of surface lime and fertilizer applications and crop residues deposition, which doesn`t occur on PC management. The PD resulted in accumulation of organic P fractions in the soil surface layer and increased all the inorganic P fractions, with larger differences for the PC in the first 10 cm layer. The PC promoted accumulation of organic P fractions of lower lability in subsurface of the clayey soils. In sandy soil the proportion of organic P fractions was much lower than in clayey soils.

The purpose of this study was to determine the economic viability of various dryland wheat tillage systems, many of which were developed from years of cooperative research efforts. In the study three conventional tillage methods were analyzed along with ten conservation tillage practices. The study farm consisted of 2000 acres, of which 1000 acres are classified as land 1 and its wheat yield is assumed to be 35 bushels per acre for non-continuous tillage methods and 23 bushels per acre for continuous tillage methods. The remaining 1000 acres are classed as land 2 and its assumed wheat yield is 30 bushels per acre for non-continuous tillage methods and 20 bushels per acre for continuous tillage practices. The farm operating conditions were changed to allow for an economic evaluation of questions that a dryland farmer would face. Questions such as: 1. do no-till chemical-fallow treatments have higher profits than do conventional tillage treatments; 2. will it pay for my farming enterprise to participate in the 1990 Farm Bills' Acreage Reduction Program (ARP); 3. what effect will be on returns to land, labor and management of a new 20-ft combine purchase, were analyzed using the Cost and Return Estimator (CARE) computer enterprise budgeting program developed for USDA-Soil Conservation Service (SCS) for each land class totaling 104 CARE budgets. A computer linear programming optimization model was run using LINDO to examine the 104 CARE budgets for an optimal tillage practice. The results are as follows: 1. Under the study assumptions chemical-fallow (no-till) treatments have higher profits than do conventional tillage treatments, if conventional tillage equipment can be adapted to no-till tillage methods. 2. Participation in the government ARP set-aside will offset the higher machinery ownership costs and thus it would pay to participate. 3 . The purchase of a new 20-ft combine or no-till Yielder drill as well as other major purchases could bankrupt a farming enterprise. It should be handled with CARE.

Conservation tillage programs have been successfully implemented for many agronomic cropping systems, but adoption of reduced tillage for vegetable crops has been slow. As many conventionally managed conservation tillage programs rely on synthetic herbicides for clean cultivation, alternative methods must be devised to suppress weed pressure and reduce reliance on mechanical cultivation to aid in the development of reduced tillage programs for organic cropping system. Strip tillage is a reduced tillage method that is well suited to vegetable crop production, and the utilization of cover crops and living mulches between rows provides a viable weed management option for organic systems. The adoption of reduced tillage and the inclusion of cover crops and living mulches have the potential to alter the agroecosystem in ways that impact plant development and crop yield, and augment weed, insect and disease pressure. The current study focuses on the use of strip tillage and the interplanting of spring-seeded living mulches and overwintered cover crops for early-season organic broccoli production. Data were collected on ground cover provided by cover crops and living mulches, crop physiological status (petiole sap nitrate, photosynthetic rate, plant growth and crop biomass) and pest pressure (weed relative abundance, insect density and disease incidence and severity). Living mulches provided the greatest ground coverage when cover crop establishment was poor; however, when cover crops produced a large amount of biomass, living mulch establishment was suppressed. Decreases in herbivorous pests and suppression of grassy and cool-season weed species were also observed, indicating that strip tillage and the use of spring-seeded living mulches and overwintered cover crops may provide beneficial pest management strategies. Decreases in crop growth and biomass, and decreases in petiole sap nitrate were observed, however, indicating reductions in crop vigor and yield may be expected with the implementation of strip tillage and living mulch crops. It is suggested that the utilization of strip tillage and living mulch crops may provide benefits to pest management which may outweigh declines in yield.

Inaug.-Diss.--Basel. / Vita. Summary in French. Includes bibliographical references.

Long-term food security and environmental quality are closely linked to maintaining soil quality. Therefore, the assessment of the effect of agricultural management practices on soil chemical, physical and biological parameters provide fundamental information about sustainability. An agricultural management practice which has received much attention in the last decade is tillage. The loss of topsoil due to erosion and a reduction of soil organic matter under conventional tillage practices, together with escalating fuel prices, have lead to the increased implementation of conservation tillage practices. However, the response of soil to a reduction in tillage is dependent on the inherent soil properties, environmental conditions, crop type and the land management practices. The successful implementation of conservation tillage practices is thus site specific. Furthermore, the effect of fertilizer application on soil quality is affected by tillage regime and therefore has important implications for recommendations of fertilizer application rates. The objectives of this study were to investigate the effect of tillage regime at three rates of nitrogen fertilization on soil microbial activity and selected soil physical properties in the Loskop area of KwaZulu-Natal, South Africa. Based on the outcomes of these investigations, recommendations regarding sustainable tillage practice and nitrogen fertilizer application rate are made. A field trial was initiated in 2003 on Gourton Farm in the Loskop area of KwaZulu-Natal on an area that was previously under annual conventional tillage and is currently planted to dry-land maize. The trial was arranged as a split plot experimental design with tillage regime (whole plots) replicated three times, and fertilizer type and application rate forming randomized subplots within the whole plots. The trial was on a clay loam soil type (Hutton soil form). The effects of annual conventional tillage (CT1) and no-till (NT) at three rates of nitrogen (N) fertilizer (as limestone ammonium nitrate (LAN)) applied at rates of 0 kg N ha-1 annum-1 (0N), 100 kg N ha-1 annum-1 (100N) and 200 kg N ha-1 annum-1 (200N) were evaluated for their effects on soil organic carbon (SOC), microbial activity, bulk density (ñb), water retention characteristics, saturated hydraulic conductivity (Ks), micro-aggregate stability and soil penetration resistance. Undisturbed soil cores were taken from three inter-rows in triplicate from each sub-plot for the A horizon (0 to 20 cm) and from three inter-rows in duplicate for the B horizon (20 to 40 cm). These undisturbed soil cores were used to determine the ñb, water retention characteristics and Ks. Bulk soil samples were collected from three inter-rows in triplicate from each sub-plot for the A (0 to 20 cm) and B (20 to 40 cm) horizons. The bulk samples from each horizon in each sub-plot were thoroughly mixed and halved. One half was used to determine microbial activity as measured by the hydrolytic and cellulolytic activity and the other half was used to determine SOC content, particle size distribution and aggregate stability. Penetration resistance was taken in duplicate in three rows in each sub-plot at 1 cm increments to a depth of 50 cm or until an instrument limiting penetration resistance of 5000 kPa was reached. Tillage regime and N application rate considerably affected soil microbial and physical properties in the A horizon (0 to 20 cm). The SOC, hydrolytic activity and ñb are significantly greater (P 0.05) effect on the soil microbial activity and physical properties except for Ks, where the Ks is significantly (P 0.05) in the B horizon on the measured soil microbial activity and physical properties except for the penetration resistance. Increasing levels of fertilizer resulted in increased penetration resistance throughout the soil profile under NT. Under CT1, this same trend is evident from below the plough layer. These results indicate that the microbial activity, as measured by hydrolytic and cellulolytic activity, is improved under NT compared to CT1. Furthermore, the soil under NT retains more plant available water (PAW) and although the ñb and penetration resistance are greater there was no obvious adverse effect on maize growth. In addition, a high rate of LAN fertilizer adversely affected soil microbial and physical properties, especially under NT. Therefore, it is proposed that NT is the preferred tillage practice in providing long-term sustainability and soil health without causing negative soil structural properties for crop productivity in the short-term. In addition, it is recommended that although increased levels of nitrogen fertilizer results in higher yielding maize plants it is unsustainable to apply high applications of LAN due to the negative effect on the soil microbial and physical properties and thus there is a need to re-evaluate the sustainability of using high rates of LAN to increase crop yields, especially under NT systems. / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2010.