Agricultural production is the main source of income and major employer in many countries in Africa, including Senegal. Commercial sweet corn (Zea mays L. ssp. saccharata) production in Senegal is increasing in response to global marketing opportunities and offers producers the ability to increase income and diversify the cropping base. Production of optimum sweet corn yield and quality depends on adequate nutrient supply, particularly, nitrogen (N). Current N recommendations are based on recommendations specific to corn for grain. This study aimed to identify tools to estimate sweet corn N status and determine the most appropriate fertilizer dosage for sweet corn. Non-destructive remote sensing tools and ion exchange resin membranes (IEMs) were used to evaluate the effect of fertilizer dose. No differences in ear yield or yield components, normalized difference vegetation index (NDVI) values, biomass, N uptake or leaf N concentration due to fertilizer dose were detected at Ndiol. However, significant relationships existed between NDVI values and yield, biomass, and N uptake at the V9 growth stage. Only yield was affected by fertilizer dose at Sangalkam, and no consistent relationships were found between chlorophyll meter readings and others measured parameters. Treatment differences due to fertilizer dose for available NH4+ at V9 (Ndiol), and NO3- at V5 (Sangalkam) were found, however further research is needed to fully evaluate the usefulness of IEMs to measure available soil N. Based on these studies, sweet corn fertilizer rates should likely be based on 75% of the dose applied to field corn, however more work is needed to confirm this finding. Pearl millet (Pennisetum glaucum (L) R. Br.) is the most widely grown staple crop in Senegal. Introduction of drought tolerant millet genotypes has helped mitigate the effect of increased water shortage in the region, but little is known about the nutritional composition of these genotypes. Our objective was to compare millet grain nutritional composition among and between putative drought tolerant and drought sensitive pearl millet lines under drought stress and well-watered conditions. One field experiment was conducted in 2014 at the National Center for Agronomic Research (CNRA) of Bambey, Senegal (16°30' and 16° 28' N; 15o44' and 15o42' W). The experiment utilized a split-plot design with four replications. Water regime was the main plot experimental factor while genotype, a total of 20 was the sub-plot. Pearl millet genotypes were divided into three contrasting groups based on drought tolerance for comparisons. Water stress did not affect 100-grain weight, test weight, protein, soluble protein, starch, sugars, amino acids or vitamin B2 content of grains among VPD-groups. Accumulation of these constituents of pearl millet grain appear to be genetically controlled and are probably not affected by late drought stress. However, differences were noted among genotypes as the sensitive VPD-group accumulated greater soluble protein, starch and soluble sugars (except sucrose) than the tolerant and medium VPD-groups. The tolerant VPD-group, however, accumulated greater protein and vitamin B2 content. Arginine, proline and serine content was greater in the sensitive VPD-group, while lysine, aspartic acid, and glutamic acid were greater in the tolerant VPD-group. Glycine, histidine, threonine, alanine, tyrosine, valine, methionine, leucine, isoleucine, and phenylalanine were relatively equal in tolerant and sensitive VPD-groups. Calcium and Na levels were affected by water stress in the sensitive VPD-group, but differently. Calcium content was greatest for the sensitive group under drought stress, while sodium was the lowest. Iron accumulation in sensitive VPD-group increased under water stress. Potassium decreased for all VPD-groups under stress, while across water regime, K levels in the drought-sensitive group were lower. Selection for drought appears to effect many of the nutritional constituents of pearl millet grain, however many of these differences appear to be directly related to parameters known to effect plant water relations. / Master of Science

M.S.

Master of Science

Cover crops (CC) are planted in between cash crops to improve soil quality and to supply nitrogen (N) to cash crops through biological N fixation or soil N scavenging. Most producers use single species CC, in part because potential benefits of using mixtures of three or more CC species are poorly understood. A three-year study was initiated at Painter, Virginia to observe effects of CC mixtures on a no-till (NT) corn (Zea mays), wheat (Triticum aestivum L.), and soybean (Glycine max) rotation to measure CC performance, N cycling, cash crop yield, and soil quality in a sandy, low organic matter soil. Twelve treatments were created with conventional tillage (CT), NT, no CC control, and monoculture or CC mixtures of 3 to 9 species. Corn was grown in year 3 in all 12 treatments and four N rates were applied (0, 56, 112 and 156 kg N ha-1). Cover crop biomass, N accumulation, CC C:N ratio, and corn and soybean yield were measured annually. Soil bulk density, compaction, infiltration rate, pH, electrical conductivity, soil respiration, earthworm counts, soil microbial respiration, and soil microbial biomass carbon (C) after three years of CC. Cover crop biomass production varied significantly each year (5633 kg ha-1 in year 1, 755 kg ha-1 in year 2, 5370 kg ha-1 in year 3) due to climate and agronomic parameters, but a CC mixture always produced the highest biomass at termination. Nitrogen accumulation was strongly correlated with biomass production (R2= 0.94) and followed the same trend due to all CC having C:N < 30:1. Corn and soybean yields in years 1 and 2 were not significantly different, but corn yield was significantly affected by treatment and N fertilizer rate in year 3. After 3 years, soil respiration, earthworm populations and soil microbial biomass C increased in CC compared to CT without CC. However, infiltration rate, bulk density, microbial respiration, pH did not improve or declined compared to CT. In conclusion, adding CC mixtures to crop rotations shows promise for producing high CC biomass, accumulating N, and increasing crop yields, while improving some soil quality parameters on sandy low organic matter soils. / Doctor of Philosophy / Cover crop (CC) are planted in between cash crops to protect the soil from erosion, improve soil quality, and supply N to next cash crop through biological N fixation or soil N scavenging. Traditionally, CC were single species, but new CC methodologies utilize mixtures of three or more species planted together to protect soils as well as produce high biomass to suppress weeds, conserve soil moisture, and improve soil quality. A long-term study was initiated in fall 2014 in Painter, VA to observe CC mixture effects on no-till (NT) corn (Zea mays), wheat (Triticum aestivum L.), and soybean (Glycine max) rotations on CC performance, N cycling, cash crop yield, and soil quality of a sandy, low organic matter soil. Twelve treatments were created that compared NT rotations with CC monocultures, CC mixtures of 3-9 species, and without CC. In the third year corn was grown in all 12 rotations and four N rates were applied (0, 56, 112 and 156 kg N ha-1). To evaluate CC mixture performance in rotations, CC biomass, CC N accumulation and corn and soybean yield was measured over three years. To evaluate changes in soil quality, nine soil physical, chemical and biological soil properties were measured after three years of NT and CC. Biomass production varied significantly each experimental year (5633 kg ha-1 in year 1, 755 kg ha-1 in year 2, 5370 kg ha-1 in year 3) due to climate and agronomic differences, but CC mixtures were the highest biomass producing CC each spring and accumulated the highest amount of N. Cover crop mixtures had equal corn and soybean yield as CC monocultures. In year 3 corn yield and was greater in treatments with CC than in treatments without CC and was greater in legume dominated monocultures and mixtures than majority grass CC mixtures and monocultures. After 3 years of CC and NT, some soil quality parameters improved. Indicators of soil biology (soil respiration, earthworm populations, and soil microbial biomass C) increased in CC treatments. However, some soil physical and chemical properties (infiltration rate, bulk density, pH and EC) did not improve. In conclusion, adding CC mixtures to crop rotations shows promise for producing high CC biomass, accumulating N, and increasing crop yields, while also improving some soil quality parameters that are important for agricultural systems.

Conversion of native forests to turfgrass-dominated residential landscapes under a wide range of management practices results in dramatic changes to vegetation and soils, which may affect soil carbon storage. To better understand the effects of landscape conversion and management on soil carbon, we conducted a study on residential properties in the Valley and Ridge physiographic province of southwest Virginia to compare soil carbon storage and dynamics between turfgrass landscapes and the surrounding mixed oak forests from which they were developed. Sixty-four residential properties ranging from 5 to 52 years since site development were investigated. Soil samples were collected from lawns and adjacent forest stands to a depth of 30 cm and analyzed for carbon and nitrogen content. Additional measurements taken were soil bulk density, temperature, moisture, and total soil CO₂ efflux rate. Homeowners participating in the study completed a survey on their lawn management practices so that the effects of specific practices (e.g. fertilization) and intensity levels on carbon dynamics could be analyzed. Also included in the survey were 11 questions regarding the homeowners' commitment to the environment. Homeowners were assigned an environmental commitment score based on their responses which was compared with lawn management practices in order to identify any connection between environmental attitude and lawn management practices. Total soil carbon content to 30 cm depth of lawn (6.5 kg C/m²) and forest (7.1 kg C/m²) marginally differed (P=0.08); however, lawn soil contained significantly greater C than forest soil at the 20-30 cm depth (0.010 vs. 0.007 g C/cm³, P=.0137). There was a weak negative relationship between carbon in the lawn and time since development at the 20-30 cm depth (P=0.08), but no significant relationship between time and C content at shallower depths. We found a positive relationship between time since development and percent C of lawn at the 0-5 cm depth (P=0.04), whereas there was a negative relationship with percent C and time at the 20-30 cm depth (P=0.03). Based on the homeowner survey, we found a positive correlation between lawn fertilization frequency and both lawn nitrogen content (P=.07) and lawn carbon content (P=.0005) in the top 0-5 cm of soil. Nitrogen content was greater in lawn than forest soil at the 0-5 cm depth (0.0025 vs. 0.0018 g/cm³³, P<.0001) and the 5-10 cm depth (0.0013 vs. 0.0009 g/cm³, P <.0001). There was a positive relationship (P=0.059) between overall environmental commitment score and level of management intensity. Higher environmental commitment (EC) score corresponded with a higher level of management intensity (fertilizer and pesticide use). Our results indicate that converting unmanaged Appalachian hardwood forest into managed, turf-grass dominated residential homesites results in similar soil organic concentration and depth distribution as the previous forest within a short period of time following development. Although total soil carbon does not differ between lawn and forest, lawn may develop greater density at 20-30cm depth over time. Fertilization enhances carbon and nitrogen content in the upper 0-5cm in lawns. Homeowners who feel that they are more strongly committed to the environment are more likely to apply higher levels of fertilizer to their lawn. / Master of Science

Early mouse (n = 501) and bovine (d = 6; n = 172) embryos were obtained to evaluate the effect of a deproteinized hemodialysate (CLBl 107) on embryo development in vitro. Bovine morulae also were cultured to examine the effect of agar embedding and the environment of immature mouse uteri on embryo development. Mouse embryos were cultured for up to 96 h in M2 medium or M2 supplemented with CLBl 107. One-and two-cell embryos did not develop beyond the two-cell stage in vitro. Degeneration of one-cell embryos occurred within 36 h. Two-cell embryos degenerated sooner when cultured in M2 plus I% CLB 1107 (27.4 ± 2.5 h) than in M2 alone (41.7 ± 3.0 h). Mean final development classification of embryos cultured from the morula stage (6) in M2 supplemented with CLBI 107 was higher (9.0 ± 2) than that for morulae (8.2 ± 1) cultured in unsupplemented M2 medium. Development of embryos cultured from the blastocyst (8) or expanded blastocyst (9) stages was not affected by treatment. Agar embedded bovine embryos were cultured in Ham's F-10 and 10% steer serum either 1) immediately after collection or 2) 24 h after storage in immature mouse uteri. Non-embedded embryos were cultured in Ham's F-10 containing 3) 10% steer serum, 4) 1% CLB 1107 or 5) 1% CLB 1107 and 10% steer serum. A greater percentage of the embryos reached the hatched blastocyst stage after culture in treatments 1, 3, 4, and 5 (38.1%, 34.6%, 28.6% and 21.1%) than embryos stored in immature mouse uteri for 24 h prior to in vitro culture (9.5%). Mean final development scores for non-embedded and agar embedded embryos cultured in Ham's F-10 and 10% steer serum were not different (5.46 ± .34 and 4.89 ± .44), but were higher than embryos cultured in CLB 1107 (4.19 ± .39), CLBl 107 and steer serum (4.22 ± .44) or immature mouse uteri (3.39 ± .43). Medium supplemented with CLB 1107 did not support mouse embryo development beyond the 2-cell stage nor did it enhance bovine embryo development. However, it appeared to enhance development of mouse morulae in vitro. Additionally, bovine morulae were not affected by agar embedding in vitro and they were able to develop following short term storage in the immature mouse uterus. / M.S.

Two experiments were conducted with field- and container-grown 'Delicious' apple trees to evaluate the effect of nitrogen fertilization on the physiology of apple leaves subjected to European red mite feeding, and the subsequent recovery of leaf function following mite removal. Nitrogen (N) fertilization affected the visual damage, and the photosynthetic response of 'Imperial Delicious' apple leaves to mite feeding. Visual damage occurred first, and remained greatest on the low N treatment throughout the experiment. High N trees exhibited a linear decline in Pn with increasing MD, in contrast to the quadratic decline found under low N treatment. With equal mite populations, high N trees retained higher Pn rates. Transpiration, dark respiration, relative water content, leaf nitrogen, and total chlorophyll were negatively related to MD, but specific leaf weight was positively related to MD. No interaction was found between N treatment and mite feeding for these parameters. Following removal of ERM populations, 'Redchief Delicious' leaves subjected to greater than 4000 MD exhibited recovery in Pn by 28 days after mite removal. Leaves receiving less MD (1500-3000) demonstrated an inconsistent response over time. Transpiration and diffusive resistance showed no recovery. Relative water content, specific leaf weight, leaf nitrogen, and total chlorophyll linearly declined with mite feeding, and were unaffected by foliar urea treatment. / Master of Science

Forests of the southeastern U.S. play an important role in meeting the increasing demand for forest products, and represent an important carbon (C) sink that can be managed as a potential tool for mitigating atmospheric CO2 concentrations and global climate change. However, realizing this potential depends on full accounting of the ecosystem carbon (C) budget. The separate evaluation of root-derived, autotrophic (RA) and microbially-derived heterotrophic (RH) soil respiration in response to management and climate change is important, as environmental and ecological factors often differentially affect these components, and RH can be weighed against net primary productivity (NPP) to estimate the C sink or source status of forest ecosystems. The objective of this research was to improve the quantitative and mechanistic understanding of soil respiratory fluxes in managed loblolly pine (Pinus taeda L.) plantations of the southeastern U.S. To achieve this overall objective, three studies were implemented to: 1) estimate the proportion and seasonality of RH:RS in four stand age classes, and identify relationships between RH:RS and stand characteristics 2) evaluate the effects of forest nutrient management and throughfall reduction on factors that influence RH and decomposition dynamics, including litter quality, microbial biomass, and enzyme activity and 3) evaluate the sensitivity of sources of RH (mineral soil-derived heterotrophic respiration; RHM, and leaf litter-derived heterotrophic respiration; RHL) to varying soil and litter water content over the course of a dry down event, and assess whether fertilization influences RH. Stand age and measurement season each had a significant effect on RH:RS (P < 0.001), but there were no interactive effects (P = 0.202). Mean RH:RS during the 12-month study declined with stand age, and were 0.82, 0.73, 0.59, and 0.50 for 3-year-old, 9-year-old, 18- year-old, and 25-year-old stands, respectively. Across all age classes, the winter season had the highest mean RH:RS of 0.85 while summer had the lowest of 0.55. Additionally, there were highly significant (P < 0.001) and strong (r > 0.5) correlations between RH:RS and peak LAI, stem volume, and understory biomass. Fertilization improved litter quality by significantly decreasing lignin:N and lignin:P ratios, caused a shift in extracellular enzyme activity from mineral soil N- and P-acquiring enzyme activity to litter C-acquiring enzyme activity, and increased microbial biomass pools. Throughfall reduction decreased litter quality by increasing lignin:N and lignin:P, but also increased C-acquiring enzyme activity. RHL was more sensitive to water content than RHM, and increased linearly with increasing litter water content (R2 = 0.89). The contribution of RHL to RH was greatest immediately following the wetting event, and decreased rapidly to near-zero between three – 10 days. RHM also had a strong relationship with soil water content (R2 = 0.62), but took between 200 – 233 days to attain near-zero RHM rates. Fertilization had no effect on RHM (P = 0.657), but significantly suppressed RHL rates after the wetting event (P < 0.009). This research provides estimates of RH:RS in managed loblolly pine systems that can be used to improve regional ecosystem C modeling efforts, and demonstrates the need to consider the impact of stand age and seasonal patterns to identify the point at which plantations switch from functioning as C sources to C sinks. Additionally, it demonstrates that the controls over RH are dynamic and influenced in the short-term by fertilization and changed precipitation regimes, with the greatest impact on properties affecting litter RH compared to mineral soil. Future research should work to improve the mechanistic understanding of the seasonal and spatial variability of RH and related controlling biotic and abiotic parameters to remedy the variability in existing RS and ecosystem C models. Understanding how management and climate change may impact factors that control RH will ultimately improve our understanding of what drives changes in forest C fluxes. / Ph. D. / Quantification of the heterotrophic component of total soil respiration is important for estimating forest carbon (C) pools and fluxes, and for understanding how silvicultural management and climate change may influence forest C dynamics. The separate evaluation of root-derived, autotrophic (R_A) and microbially-derived heterotrophic (R_H) soil respiration is necessary, as environmental and ecological factors often differentially affect these components, and R_H can be weighed against net primary productivity (NPP) to estimate the C sink or source status of forest ecosystems. This research examined the dynamics of R_H in loblolly pine plantations of the southeastern U.S., and the drivers of RH and organic matter decomposition in response to forest management (fertilization) and reduced precipitation (throughfall reduction) to improve the quantitative and mechanistic understanding of this important C flux. This work provided estimates of R_H in managed loblolly pine systems that can be used to improve regional ecosystem C modeling efforts, and demonstrates the need to consider the impact of stand age and seasonal patterns to identify the point at which plantations switch from functioning as C sources to C sinks. Additionally, it demonstrates that the controls over R_H, such as substrate quality and microbial community activity and biomass, are dynamic and influenced in the short-term by fertilization and altered moisture availability, with the greatest impact on properties affecting forest floor R_H compared to mineral soil R_H. Future research should work to improve the mechanistic understanding of the seasonal and spatial variability of R_H and related controlling biotic and abiotic parameters to remedy the variability in existing R_S and ecosystem C models. Understanding how management and climate change may impact factors that control R_H will ultimately improve our understanding of what drives changes in forest C fluxes.

Orientador: Mara Cristina Pessôa da Cruz / Resumo: Nas áreas de cultivo de cana-de-açúcar em que se empregam mudas pré-brotadas, o transplantio é um momento crítico, e há necessidade de adoção de práticas de manejo que levem ao enraizamento rápido, de modo que irrigações suplementares possam ser reduzidas ou dispensadas. A adubação, sobretudo o uso de fósforo e de nitrogênio, pode ser um fator de aceleração do enraizamento. Deste modo, objetivou-se, com o presente estudo, avaliar o enraizamento de mudas pré-brotadas de cana-de-açúcar em função do fornecimento de nitrogênio e fósforo, buscando a redução de tempo para o início da emissão radicular após o transplantio. O experimento foi conduzido em casa de vegetação, utilizando amostra da camada superficial (0-20 cm) de solo de textura média, com baixo teor de fósforo. Os tratamentos foram arranjados em esquema fatorial com três fatores (doses de nitrogênio, doses de fósforo e tempos de crescimento), em delineamento inteiramente ao caso com cinco repetições. As doses de nitrogênio e fósforo foram equivalentes a 0 e 100 mg dm-3, e os tempos de crescimento foram 7, 14, 21 e 28 dias. O experimento foi conduzido empregando mudas do cultivar RB97 5201, produzidas em condições comerciais. Em cada data de avaliação foram determinados comprimento, área, diâmetro médio e densidade de raízes, matéria seca de raízes e da parte aérea e concentrações e acúmulos de nitrogênio e de fósforo na parte aérea. O aumento da concentração de nitrogênio no solo promoveu diminuição no diâmetro das raíz... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: In sugarcane cultivation areas where pre-sprout seedlings are used, transplanting is a critical moment and there is a need to adopt methods that lead to fast rooting, so that additional irrigations can be minimized or dispensed. Fertilization, especially the use of phosphorus and nitrogen, can be a factor of rooting acceleration. Thus, the objective of the present study was to evaluate the rooting of pre-sprouted sugarcane seedlings due the supply of nitrogen and phosphorus, aiming to reduce the time to start root emission after transplanting. The experiment was carried out in a greenhouse, using a sample of sandy loam topsoil layer (0-20 cm) with low phosphorus content. The treatments were arranged in a factorial scheme with three factors (nitrogen doses, phosphorus doses and growth times), in a full design with five replicates. The nitrogen and phosphorus doses were equivalent to 0 and 100 mg dm-3 N or P, and growth times were 7, 14, 21 and 28 days. The experiment was conducted using seedlings of cultivar RB97 5201, produced under commercial conditions. At each evaluation date, length, area, root average diameter, root density, dry matter in roots and shoot, and concentration and accumulation of nitrogen and phosphorus in shoot were determined. The increase in concentration of nitrogen in the soil promoted the reduction of root diameter in the sugarcane seedlings at 28 days after transplantation. The increase in concentration of phosphorus in the soil decreased the area, di... (Complete abstract click electronic access below) / Mestre

Os estudos de adubação com zinco foliar em citros desenvolvidos no Brasil são na maioria das vezes limitados às informações das quantidades dos nutrientes absorvidos pelas folhas, porém o transporte do zinco das folhas para outras partes das plantas ainda precisa ser esclarecido. A maioria das investigações sobre tal assunto é vasta de resultados conflitantes. Em vista disso, o uso da técnica com isótopos estáveis é uma ferramenta viável para auxiliar na determinação direta da absorção e translocação de zinco aplicado via foliar no citros. O presente estudo tem como objetivos determinar (i) os teores de zinco nas folhas durante três dias após a pulverização; na fase de floração e frutificação do citros: (ii) teores e acúmulos de zinco nas folhas e frutos; (iii) concentração de zinco nos pluviolixiviados das folhas; (v) absorção e translocação do zinco proveniente das fontes nas folhas; (vi) translocação do zinco proveniente das fontes nos frutos; (vi) concentrações de zinco nos pluviolixiviados das folhas provenientes das fontes.Foram conduzidos dois experimentos na Estação Experimental de Citricultura de Bebedouro-SP. No primeiro experimento foram avalidas cinco fontes foliares de zinco, EDTA, sulfato, fosfito, quelado aminoácido (AA) e cloreto. No segundo foram avaliadas três fontes enriquecidas com 68Zn, EDTA, fosfito e sulfato, pulverizada na fase de floração e frutificação do citros. Para determinar os pluviolixiviados das folhas nos dois experimentos, colocaram-se recipientes plásticos embaixo das árvores. No experimento 1, todas as fontes aumentaram os teores foliares de Zn. O cloreto de zinco elevou os teores nas folhas novas, frutos novos e maduros. Observou-se que houve lavagem do zinco das folhas pelas chuvas, porém independe da fonte aplicada e depende do tempo decorrido depois da aplicação. Há perda de 11% do zinco aplicado nas folhas pela água da chuva. O zinco proveniente da fonte EDTA foi maior nas folhas novas e frutos novos, colhidos na fase de floração. Na fase de frutificação para os frutos maduros não houve diferença entre o zinco proveniente das fontes. / Studies of zinc fertilization on citrus foliar developed in Brazil are mostly limited to information of the nutrients quantities absorbed by the leaves, but the zinc transport of the leaves to other parts of the plants need to be clarified. Most investigations on this subject is vast array of conflicting results. As a result, the use of stable isotope technique is a viable tool to assist in the direct determination of zinc uptake and translocation of foliar application in citrus.The present study has as objective to determine: (i) the levels of zinc in leaves during three days after spraying, at flowering and fruiting stage of citrus; (ii) levels and accumulation of zinc in leaves and fruits; (iii) concentration of zinc in rainfall leached of the leaves; (iv) uptake and translocation of zinc from the sources in the leaves; (v) translocation of zinc from the sources in the fruits; (vi) rainfall leached zinc concentrations of the leaves from those sources. Two experiments were conducted at the Experimental Station of Citrus - Bebedouro - SP. In the first experiment were evaluated five foliar sources of zinc, EDTA, sulfate, phosphite, chelated amino acid (AA) and chloride. In the second were evaluated three sources enriched with 68Zn, EDTA, phosphite and sulfate sprayed at flowering and fruiting of citrus. To determine the rainfall leached of the leaves in both experiments, plastic containers were placed under the trees. In experiment 1, all sources increased foliar concentrations of Zn. The zinc chloride increased the levels in young leaves, young fruit and mature. It was observed that there washing of the zinc in the leaves by rain, but independent of the applied source and depends on the time elapsed after application. There is loss 11% of zinc applied to the leaves by rainwater. Zinc from the source EDTA was greater in young leaves and fruits, harvested at flowering stage. During fruiting for the ripe fruit there was no difference among the zinc from the sources.