Carbon isotope discrimination (?13C) may be an appropriate measure for determination of the water use efficiency (WUE) of plants. This work confirms the negative correlation of ?13C and WUE in selected genotypes of barley and wheat. It also deals with the suitability of using the observed relationship in breeding of drought resistant crops.

Submitted by Emanuel Varela Cardoso (emanuel.varela@ufcg.edu.br) on 2018-05-08T20:54:39Z No. of bitstreams: 1 PATRÍCIA FERREIRA DA SILVA – TESE (PPGEG) 2017.pdf: 1557927 bytes, checksum: ee25e36e22f91a54e1893276f23dfea7 (MD5) / Made available in DSpace on 2018-05-08T20:54:39Z (GMT). No. of bitstreams: 1 PATRÍCIA FERREIRA DA SILVA – TESE (PPGEG) 2017.pdf: 1557927 bytes, checksum: ee25e36e22f91a54e1893276f23dfea7 (MD5) Previous issue date: 2017-02-08 / CNPq / A palma é uma das principais forrageiras utilizadas na alimentação animal no Semiárido nordestino brasileiro, além de poder ser fonte inovadora para a produção de biocombustível. Objetivou-se, com o presente, estudo avaliar o desempenho da palma forrageira sob diferentes lâminas de irrigação e adubação nitrogenada. O experimento foi conduzido em condições de campo no munícipio de Santa Luzia – PB, na fazenda Poço Redondo. O delineamento experimental foi o de blocos casualizados em esquema fatorial 5 x 5, constituído de cinco lâminas de irrigação (125; 100; 75; 50 e 25% da ET 0), cinco níveis de adubação nitrogenada (0; 150; 300; 450 e 600 kg ha-1de N), com três repetições, totalizando 75 unidades experimentais. Foram avaliados, ao longo do experimento, número, comprimento, largura e espessura de cladódios, altura e largura de planta, taxas de crescimento absoluto e relativo, área e índice de área de cladódios, biomassa verde de cladódios, produtividade estimada não destrutiva e destrutiva, e eficiência do uso da água da palma forrageira. Os dados obtidos foram analisados pelo teste F e análise de regressão polinomial. A lâmina de irrigação influenciou, de forma significativa, as variáveis de crescimento da palma forrageira estudadas, exceto o número de cladódios. As diferentes doses de adubação nitrogenada, aplicadas, via fertirrigação, influenciaram, de forma significativa, as variáveis de crescimento da palma forrageira, excetuando-se o comprimento e a área de cladódio. A maior produtividade estimada não destrutiva, destrutiva e a máxima eficiência do uso da água de palma forrageira cultivar orelha de elefante mexicana foram obtidas na associação lâmina de irrigação de 125% da ET0 , total de (371,09 mm) e na dose de nitrogênio de 600 kg ha-1. A eficiência no uso da água e do nitrogênio média foi de 13,9 kg m-3 de água aplicada via fertirrigação em um ano de condução do trabalho. A média de produtividade estimada não destrutiva e a destrutiva foram 700 t ha-1 aos 150 dias após a aplicação dos tratamentos e 299 t ha-1 ano -1. Nas condições de semiaridez com temperatura média de 27,6°C a palma forrageira responde tanto a irrigação quanto a adubação nitrogenada. Recomenda-se o corte da palma forrageira duas vezes ao ano, quando submetida a adubação nitrogenada e irrigação. / The palm is one of the main forages used in animal nutrition in the Brazilian Northeastern semiarid region, besides being an innovative source for the production of biofuel. The objective of this study was to evaluate the performance of forage palm under different irriga tion and nitrogen fertilization. The experiment was conducted under field conditions in the Municipality of Santa Luzia - PB, at the Poço Redondo farm. The experimental design was a randomized complete block design in a 5 x 5 factorial scheme, consisting of five irrigation slides (125, 100, 75, 50 and 25% of ET0), five levels of nitrogen fertilization (0, 150, 300, 450 e 600 kg ha-1 of N), with three replicates, totaling 75 experimental units. Number, length, width and thickness of cladodes, plant height and width, absolute and relative growth rates, area and cladode area index, cladode green biomass, estimated non-destructive and destructive productivity were evaluated throughout the experiment and efficiency of forage palm water use. The data were analyzed by the F test and polynomial regression analysis. The irrigation blade significantly influenced the growth variables of the forage palm studied, except for the number of cladodes. The different doses of nitrogen fertilization, applied via fertigation, significantly influenced the growth variables of the forage palm, except for the length and the cladode area. The highest estimated non destructive, destructive and maximum efficiency of the use of forage palm water for cultivating Mexican elephant ear were obtained in the association of irrigation depth of 125% of ET 0, total of (371.09 mm) and nitrogen dose of 600 kg ha-1. In semiarid conditions with average temperature of 27.6 ° C the forage palm responds to both irrigation and nitrogen fertilization. It is recommended the cutting of the forage palm twice a year, when submitted to nitrogen fertilization and irrigation.

Com a continuação do aquecimento global, prevê-se o aumento dos períodos de seca, um dos mais importantes fatores abióticos a afetar o crescimento dos eucaliptos no Brasil. Nessa direção, as práticas silviculturais poderiam adaptar-se para favorecer os mecanismos de adaptação das árvores à seca. Assim, na Estação Experimental de Itatinga, foram avaliados os efeitos da adubação potássica sobre os aspectos produtivos e fisiológicos de um povoamento de Eucalyptus grandis, em primeira rotação, submetido à exclusão parcial de chuva durante trinta meses após o plantio. O dispositivo experimental foi um split plot, com três blocos completos e quatro tratamentos: dois regimes hídricos (100% e 63% das chuvas, com exclusão parcial artificial) e duas doses de K (0 e 4,5 kmol ha-1). A meta foi avaliar a influência da nutrição potássica sobre as características e a atividade fotossintética das folhas. A transpiração foi medida por sensores de fluxo de seiva para estimar a eficiência de transpiração do povoamento. O potencial foliar e as trocas gasosas foliares foram monitorados, enquanto os valores de \'delta\'13C do floema foram medidos, para avaliar o estado hídrico e o funcionamento estomático das árvores, em função da disponibilidade de K e de água. Os resultados mostraram que a adição de K atuou sobre vários mecanismos responsáveis pelo aumento do crescimento e da produção de madeira: aumento da área foliar total e individual, da duração de vida foliar, do tamanho e da turgescência celular foliar, da espessura foliar e dos espaços intercelulares no mesófilo foliar, da capacidade fotossintética, da condutância dos estômatos e do mesófilo, da exportação dos fotoassimilados, produzidos nas folhas-fontes, do fluxo de seiva, da eficiência de transpiração na produção de madeira, pelo aumento da repartição de biomassa nesse compartimento. Folhas com sintomas de deficiência de K mostraram concentrações de nutrientes, espaços intercelulares e atividade fotossintética inferiores, e concentrações de açúcares solúveis superiores, na comparação com o tratamento com K, sugerindo uma ligação entre nutrição, anatomia e fisiologia foliar. Durante o déficit hídrico, o E. grandis mostrou um comportamento isohidrodinâmico, associado ao fechamento estomático, ao ajustamento foliar osmótico, à diminuição na elasticidade das paredes celulares, ao aumento na eficiência de uso da água nas folhas, à diminuição da área foliar total e à rápida absorção da água nas camadas profundas do solo. A partir de aproximadamente 22 meses após o plantio, o estado hídrico das árvores diminuiu: (1) nas parcelas com exclusão parcial de chuva, em relação às parcelas sem exclusão parcial de chuva, e (2) nas parcelas com adição de K, em relação às parcelas sem essa adição. Embora a adição de K melhore as relações hídricas nas folhas, o controle dos movimentos estomáticos e as trocas gasosas foliares, ela agravou o estado hídrico das árvores durante períodos de seca intensa, devido ao maior crescimento e à demanda hídrica. Assim, os efeitos benéficos da adição de K sobre a adaptação à seca das árvores poderiam não contrabalançar o aumento do déficit hídrico durante períodos mais intensos de seca. Em relação às previsões futuras de seca, as empresas florestais, provavelmente, terão de adaptar a fertilização para minimizar a demanda de água e os riscos de mortalidade / Global warming is predicted to exacerbate drought, one of the most important abiotic stress factors affecting eucalypts growth in Brazil. Silvilcultural practices might be adapted to enhance drought adaptation mechanisms of trees. This study examined the effects of K addition on productive and physiological aspects of Eucalyptus grandis stands in first rotation submitted to partial through fall exclusion over thirty months after planting. A large-scale through fall exclusion experiment using a split plot design was conducted with three blocks and four treatments: two water regimes (100% and 63% of through fall with partial artificial exclusion) and two K doses (0 and 4.5 kmol ha-1). The influence of K nutrition on characteristics and photosynthetic activity of leaves was assessed Tree transpiration was measured from sap flow probes to estimate water use efficiency. Foliar water potential and gas exchange were monitored, and phloem \'delta\'13C was measured in order to evaluate tree water status and stomatal regulation depending on K and water availabilities. The results showed that K supply influence various mechanisms responsible for tree growth enhancement: increase in total and individual leaf area, leaf lifespan, cell turgor and cell size due to an increase in turgor, leaf thickness and intercellular spaces, photosynthetic capacity, stomata and mesophyll conductances, photoassimilate export from source leaves and transpiration efficiency for wood production through increase of biomass partitioning to this compartment. Leave with K-deficiency symptoms exhibited lower nutrient concentrations and photosynthetic activity, reduced intercellular spaces, and higher soluble sugar contents compared to healthy leaves, which suggested a strong link between nutrition, leaf anatomy and physiology. The adaptive mechanisms of E. grandis trees to cope with water restriction were an isohydrodynamic behavior associated with stomatal closure, osmotic adjustment, a decrease in wall cell elasticity, an increase in foliar water use efficiency, a decrease in total leaf area and a fast water uptake in very deep soil layers. From approximately 22 months after planting onwards, tree water status was lower: (1) in droughted plots compared to the rain-fed plots and, (2) in K-fertilized plots, compared to the K-unfertilized trees. Although K addition enhanced tree water relations, stomatal control and leaf gas exchange, it exacerbated tree water deficit during severe drought as a result of high water demand throughout tree development. Therefore, the beneficial effects of K supply on tree acclimation to drought may not counterbalance the increase in water deficit during severe water restriction periods compared to the K-unfertilized trees. Regarding future drought previsions, forest managers might have to adapt their fertilization regimes to minimize water demand and risks of mortality

FundaÃÃo de Amparo à Pesquisa do Estado do Cearà / Como todas as demais atividades agropecuÃrias, a criaÃÃo de pequenos ruminante à geradora de resÃduos que, manejados inadequadamente, acarretam em impactos negativos ao meio ambiente. Entretanto, vale salientar que, quando corretamente manejados, os resÃduos oriundos da ovinocaprinocultura apresentam alto potencial como insumos agrÃcolas. Objetivou-se avaliar as caracterÃsticas morfofisiolÃgicas de Pennisetum purpureum cv Cameroon irrigado e submetido a doses de composto orgÃnico proveniente de resÃduos da produÃÃo e do abate de pequenos ruminantes. O experimento foi realizado em capineira de capim-elefante, na Embrapa Caprinos e Ovinos, Sobral-CE. Os tratamentos foram doses do composto orgÃnico (0; 13,3; 26,6; 39,9; 53,2; 79,8 tha-1), alÃm de um tratamento mineral de nitrogÃnio e potÃssio numa dose equivalente a 720 e 900 kgha-1ano-1, respectivamente. Utilizou-se o delineamento em blocos completos casualizados em esquema de parcelas subdivididas, com medidas repetidas no tempo, onde as parcelas corresponderam a sete doses de composto orgÃnico e um tratamento adicional (adubaÃÃo mineral) e, as subparcelas, quatro ciclos de crescimento da cultura. A eficiÃncia quÃntica potencial (FV/FM) apresentou valor de 0,75 na dose de 79,8 tha-1. PorÃm, a razÃo de decrÃscimo da fluorescÃncia (Rfd) respondeu de maneira quadrÃtica nos ciclos 1 e 2, denotando bom funcionamento do aparato fotossintÃtico ao longo dos ciclos. Nos ciclos 1 e 2, foi verificado a taxa de acÃmulo de forragem mÃxima de 278,9 kg de MSha-1dia-1, na dose de 70,63 tha-1. As variÃveis biomassa de lÃmina foliar verde (BLV) e de colmo verde (BCV) apresentaram comportamento quadrÃtico no ciclo 1, com ponto de mÃximo nas doses 67,73 e 63,05 tha-1, respectivamente. Comportamento semelhante foi verificado para as variÃveis eficiÃncia de uso Ãgua para produÃÃo de lÃmina (EUABLV) e de colmo (EUABCV), com ponto de mÃximo nas doses 62,94 e 60,28 tha-1 do composto. A anÃlise de contraste entre as doses do composto orgÃnico x adubaÃÃo mineral nÃo revelou efeito no primeiro ciclo para a maioria das variÃveis analisadas. Conclui-se que devido à alta taxa de mineralizaÃÃo do nitrogÃnio do composto orgÃnico nos dois primeiros ciclos de crescimento, hà a necessidade da suplementaÃÃo com o uso de adubaÃÃo nitrogenada nos ciclos subsequentes, com o propÃsito de garantir a manutenÃÃo da produtividade. / Similarly to other agricultural activities, small ruminant farming produces waste that, if managed improperly, results in negative environmental impacts. However, when properly managed, sheep and goat farming waste have a high potential to be used as agricultural inputs. This study evaluated the morphological and physiological characteristics of Pennisetum purpureum cv. Cameroon irrigated and subjected to different levels of organic compost from waste production and slaughter of small ruminants. The experiment was conducted in a cut and carry elephant grass at Embrapa Goats and Sheep, Sobral-CE. The treatments consisted of different levels of the organic compost (0; 13,3; 26,6; 39,9; 53,2; 79,8 tha-1) besides a mineral treatment of nitrogen and potassium equivalent to 720 and 900 kgha-1year-1 , respectively. This was a split-plot randomized complete block design with repeated measures over time, in which the plots corresponded to seven levels of organic compost and an additional treatment (mineral fertilization), and the subplots to four crop growth cycles. The potential quantum efficiency (Fv/Fm) showed a value of 0,75 at a level of 79,8 tha-1. The fluorescence decrease ratio (Rfd) responded quadratically in cycles 1 and 2, indicating proper functioning of the photosynthetic apparatus over the cycles. In cycles 1 and 2, it was observed the maximum forage accumulation rate of 278,9 kg DMha-1day1 at a level of 70,63 tha-1. Biomass of leaf blades (LDB) and green stems (GCB) presented a quadratic response in cycle 1, with maximum point at the levels 67,73 and 63,05 tha-1, respectively. Similar behavior was found for the variables water use efficiency for blade production (WUELDB) and stem (WUEGCB), with maximum point at the levels 62,94 and 60,28 tha-1 compost. The contrast analysis between the levels of the organic compost x mineral fertilization evidenced no effect in the first cycle for most variables. In conclusion, due to the high rate of mineralization of nitrogen from the organic compost in the first two growth cycles, there is need for supplementation with nitrogen fertilizer in subsequent cycles, for the purpose of maintaining productivity.

As exigências do potássio para maximizar o crescimento do eucalipto têm sido intensivamente estudadas pelas empresas florestais através de experimentos empíricos. Embora, ainda existe um fraco entendimento dos processos envolvidos com a resposta à adubação com potássio, conduzindo a resultados contraditórios entre a disponibilidade do potássio no solo e as respostas do eucalipto segundo o encontrado na literatura. Existe a hipótese que grandes depósitos de sódio perto ao mar, poderiam conduzir numa substituição parcial do potássio pelo sódio na fisiologia do eucalipto, considerando que respostas ao sódio têm sido observadas em ambientes pobres de potássio. Portanto, o objetivo deste trabalho foi avaliar a resposta de plântulas de Eucalyptus grandis a adubação tanto de potássio quanto de sódio, além de ser submetidas a teores de umidade de -0.07 MPa e -0.6 MPa. Mudanças na partição de assimilados, eficiência no uso da água (EUA) e trocas gasosas foram determinadas em casa de vegetação, nas idades de dois, quatro e seis meses após a adubação. O estresse hídrico afetou a produção de matéria seca para todos os tratamentos. Não obstante, o potássio ajudou na osmoregulação sob condições de estresse, encontrando uma produção de matéria seca significativamente superior ao testemunho sem aplicação de potássio nem sódio. Além disso, a resposta do eucalipto ao sódio indicou uma alta condutância estomática que foi refletida numa alta transpiração, sendo um comportamento de má adaptação para condições de estresse hídrico. / The requirements of potassium fertilization to maximize the growth of eucalyptus stands have been extensively studied by forest companies through empirical experiments. Nevertheless, there is a poor understanding of the processes involved in the response of trees to K+ fertilization, leading to contradictory results in the literature between the availability of K+ in the soil and the responses of eucalyptus plantations to K+ inputs. The hypothesis that large amounts of Na+ atmospheric deposits close to the sea could result in a partial replacement of K+ by Na+ in the physiology of eucalyptus has been made, since a response to Na+ fertilizer application has been observed in soils with very low exchangeable K+ contents. The present study aimed to assess the response of Eucalyptus grandis cuttings to K+ and Na+ fertilizations, for two level of soil water potential: -0,07 MPa and -0,6 MPa. Changes in dry matter partition, water use efficiency (WUE), and gas exchange were determined in a greenhouse experiment, two, four and six months after treatment establishment. The water stress influenced the dry matter production whatever the fertilization type. However, the potassium application improved the osmotic adjustment under conditions of stress, leading to a production of dry matter significantly higher than in the control treatment without K+ and Na+ application. Moreover, Na+ application increased the stomatal conductance of eucalyptus plants, leading to high transpiration rates, indicating that Na+ inputs lead to a tree behavior badly adapted to water stress conditions.

Le principal objectif de ce travail était de déterminer l’efficience d’utilisation de l’eau (WUE) de diverses espèces d’acacias d’origine Australienne et Sahélienne par la discrimination isotopique au niveau de la feuille (Δ13Cf) et par différentes techniques de mesure. Les acacias ont montré une forte variabilité interspécifique de Δ13Cf. Cette variabilité a été confirmée par les mesures directes d’échanges gazeux au niveau des feuilles (efficience intrinsèque d’utilisation de l’eau, Wi) et par des mesures effectuées au niveau de la plante entière (efficience de transpiration, TE). Une forte variabilité interspécifique des traits foliaires(densité stomatique DS, proportion d’azote dans les feuilles %N, surface massique SLA, assimilation nette du CO2 à la saturation Asat, conductance stomatique en vapeur d’eau à la saturation gssat) et de la croissance (ratio biomasse racinaire sur biomasse aérienne R/S) a également été constatée entre les espèces. WUE était pratiquement contrôlée par gssat.L’hypothèse selon laquelle les espèces se développant dans les zones arides présenteraient une WUE plus élevée n’a pas été vérifiée. Au contraire, les espèces des zones semi-humides ont présenté une WUE plus élevée que celles de zones semi-arides et arides. / The main objective of this work was to compare water use efficiency (WUE) among various Australian and Sahelian acacia species using isotope discrimination at leaf level (Δ13Cf) and various methods of measurement. Acacia species exhibited a large inter-specific variability of Δ13Cf. This variability was confirmed by direct leaf gas exchange measurements (intrinsic water use efficiency, Wi) and by measurement at the whole plant level (transpiration efficiency, TE). A large interspecific variability of leaf traits (stomatal density DS, leaf nitrogen concentration %N, specific leaf area SLA, net CO2 assimilation of the saturation Asat, stomatal conductance for water vapor of the saturation gssat) and growth characteristics (root shoot biomass ratio R/S) has also been reported. WUE was controlled for gssat. The hypothesis that the species from arid areas exhibit higher WUE was not confirmed. In contrast, the species from semi-wet area exhibited a higher WUE than those from semi-arid and arid zones

Salinity continues to be one of the world’s most serious environmental problems in agriculture. The increasing world population and urbanization are forcing farmers to utilize marginal lands as well as poor quality water. One of the strategies in dealing with salinity is growing salt tolerant plants and there has been increased need to understand the effects of salinity on crops. Owing to its high nutritive value and wide adaptability to diverse environments, amaranth is considered a promising crop for marginal lands and semiarid regions. The objective of the study was to investigate the response of amaranth to salinity stress and evaluate stress amelioration by calcium and seed priming. Salinity tolerance during germination and early seedling growth was examined for six genotypes of amaranth (Amaranthus species) at different salt concentrations ranging from 0 to 200 mM NaCl or Na2SO4. Enhancement of germination was observed at 25 mM, while increasing salt concentrations reduced the germination percentage as well as germination rate. A.tricolor and Accession ’83 were able to germinate in 200 mM NaCl while there was no germination at 200 mM Na2SO4 in all the genotypes. Overall, Accession ’83 was the most resistant and A. hybridus the most sensitive genotype, particularly at high salt concentrations. Inhibition of germination was greater in Na2SO4 than in NaCl salinity treatments. Amaranth was more salt tolerant at germination than at seedling growth. Seedling emergence, survival and growth were reduced by salinity and at much lower concentrations than at seed germination. Differences in salt tolerance were noted among the genotypes. Salinity stress was initiated at different growth stages (cotyledon stage, 2-leaf stage and 4-leaf stage) in order to determine whether tolerance of amaranth differs with the stage of development. The treatment either continued until termination of the experiment or for 14 days at each stage. Amaranth plants were less sensitive to salinity when the stress was initiated at the 4-leaf stage. Lower salt concentrations had less detrimental effects than higher concentrations when applied at the cotyledon stage. Application of low salt concentration at cotyledon stage for 14 days did not have any effect on plant growth. The results indicate that it is feasible to use saline water for growing amaranth with minimum yield losses if salt concentration, duration of exposure and time of salinization are carefully managed. Differences in salinity tolerance among amaranth genotypes were analyzed in terms of plant survival, growth, gas exchange, water use and leaf anatomical changes. A. hypochondriacus and A. cruentus showed greater tolerance to salinity since they survived in 200 mM NaCl treatment and the reduction in growth at 50 and 100 mM was lower than that of A. tricolor and Accession ’83. A. hypochondriacus and A. cruentus were more efficient water users and partitioned photosynthates towards shoot growth as opposed to the other two genotypes. Photosynthetic rate, stomatal conductance, stomatal density and apertures were reduced by salinity but were higher in A. tricolor than in A. cruentus. Salinity resulted in A. cruentus developing thicker leaves compared to A. tricolor. Productivity on saline soils can be increased by growing genotypes more tolerant to salinity. The interactive effect of salinity and water stress on amaranth plant growth was evaluated. It was found that the reduction in shoot growth was greater in plants submitted to water stress than in those submitted to salt or salt + water stress. Water use efficiency was increased while leaf water and osmotic potentials were reduced by the salinity stress treatments. In drying soil plants previously salinized had a greater degree of osmotic adjustment, so that plants were able to continue growth for a longer period compared to water stressed plants. The effect of calcium in ameliorating salt stress was investigated. Supplementary calcium, either as CaSO4 or CaCl2 ameliorated the negative effects of salinity on growth, gas exchange, membrane permeability and mineral uptake. In a separate experiment it was shown that it is feasible to mitigate the adverse effects of salinity on amaranth seed germination, seedling survival and growth by seed priming and that the positive effect of priming persisted to vegetative growth stage. Priming with CaSO4 + NaCl showed a greater positive response than priming with the individual salts. / Thesis (PhD (Plant Production andSoil Science))--University of Pretoria, 2007. / Plant Production and Soil Science / unrestricted

A series of field, rainshelter, growth cabinet and modelling studies were conducted to investigate hot pepper response to different irrigation regimes and row spacings; to generate crop-specific model parameters; and to calibrate and validate the Soil Water Balance (SWB) model. Soil, climate and management data of five hot pepper growing regions of Ethiopia were identified to develop irrigation calendars and estimate water requirements of hot pepper under different growing conditions. High irrigation regimes increased fresh and dry fruit yield, fruit number, harvest index and top dry matter production. Yield loss could be prevented by irrigating at 20-25% depletion of plant available water, confirming the sensitivity of the crop to mild soil water stress. High plant density markedly increased fresh and dry fruit yield, water-use efficiency and dry matter production. Average fruit mass, succulence and specific leaf area were neither affected by row spacing nor by irrigation regimes. There were marked differences among the cultivars in fruit yields despite comparable top dry mass production. Average dry fruit mass, fruit number per plant and succulence were significantly affected by cultivar differences. The absence of interaction effects among cultivar and irrigation regimes, cultivars and row spacing, and irrigation regimes and row spacing for most parameters suggest that appropriate irrigation regimes and row spacing that maximize productivity of hot pepper can be devised across cultivars. To facilitate irrigation scheduling, a simple canopy cover based procedure was used to determine FAO-type crop factors and growth periods for different growth stages of five hot pepper cultivars. Growth analysis was done to calculate crop-specific model parameters for the SWB model and the model was successfully calibrated and validated for five hot pepper cultivars under different irrigation regimes or row spacings. FAO basal crop coefficients (Kcb) and crop-specific model parameters for new hot pepper cultivars can now be estimated from the database, using canopy characteristics, day degrees to maturity and dry matter production. Growth cabinet studies were used to determine cardinal temperatures, namely the base, optimum and cut-off temperatures for various developmental stages. Hot pepper cultivars were observed to require different cardinal temperatures for various developmental stages. Data on thermal time requirement for flowering and maturity between plants in growth cabinet and open field experiments matched closely. Simulated water requirements for hot pepper cultivar Mareko Fana production ranged between 517 mm at Melkassa and 775 mm at Alemaya. The simulated irrigation interval ranged between 9 days at Alemaya and 6 days at Bako, and the average irrigation amount per irrigation ranged between 27.9 mm at Bako and 35.0 mm at Zeway. / Thesis (PhD)--University of Pretoria, 2010. / Plant Production and Soil Science / unrestricted

Water availability and arable lands are increasingly limiting resources in many parts of the U.S., particularly in semi-arid and arid regions. As a means of addressing food and fuel demands associated with burgeoning population growth, highly productive and water-use efficient crops need to be identified. One potential crop, Agave, merits consideration and evaluation due to its putative capability to provide sustenance and energy despite growing in water-limited regions and on marginal soils. However, little is known regarding the productivity these succulent plants will have under growing conditions of the Southwest, where high concentrated saline soils are abundant, and water is often limited. The objectives of these studies were to determine the effects of high levels of salinity and different volumetric water content levels (VWC) on plant growth, biomass accumulation, and nutrient uptake. I used a hydroponic study to compare the effects of four salinity treatments (0.5, 3, 6, and 9 dS m-1) on productivity of four Agave species (Agave parryi, Agave utahensis ssp. kaibabensis, Agave utahensis ssp. utahensis, and Agave weberi). In a second study, an automated irrigation system was established to examine four pre-determined VWC threshold set-points and simulated a gradient of well-watered to drought conditions, to evaluate how A. weberi would respond to varying levels of water availability. Salinity concentrations did not significantly affect root and plant dry weight accumulation in A. weberi, but all other agave plants experienced less biomass accumulation under high saline conditions (>6 dS m-1). Seedlings of A. utahensis were two times more likely to die in the two highest saline treatments (6 and 9 dS m-1) than the two lower treatments (0.5 dS m-1 and 3 dS m-1). Calcium, Mg, S, Mn levels decreased in both A. parryi and A. weberi at higher salinity levels. Agave weberi was able to tolerate salinity, but it also experienced lower biomass production ≤3 dS m-1. In the water-stress study, Agave weberi plants experienced a decrease of 2.11 g as compared to plants in the highest treatment. Plants in the intermediate VWC treatments had similar dry mass values as those in the highest treatment, which suggests that this species could have moderately high yields under limited water conditions, and consequently should be evaluated as a potential bioenergy crop for semi-arid regions, such as the U.S. Southwest. Agave shows considerable potential to be grown in arid and semi-arid regions that are moderately high in salinity and have limited water availability. Indeed, the cultivation of Agave as a crop appears to be a viable option for many areas of the Southwest. While some of the Agave species evaluated were quite productive under moderate salt and water stress, it is uncertain if growth will be significantly reduced if under these stress conditions for periods longer than 3 months.

No description available.