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.

Submitted by Luciana Ferreira (lucgeral@gmail.com) on 2017-02-08T10:12:21Z No. of bitstreams: 2 Dissertação - Gustavo de Melo Oliveira Gonçalves - 2016.pdf: 1630959 bytes, checksum: 90d5f7c22407381803a1e520c265c080 (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) / Approved for entry into archive by Luciana Ferreira (lucgeral@gmail.com) on 2017-02-08T10:12:49Z (GMT) No. of bitstreams: 2 Dissertação - Gustavo de Melo Oliveira Gonçalves - 2016.pdf: 1630959 bytes, checksum: 90d5f7c22407381803a1e520c265c080 (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) / Made available in DSpace on 2017-02-08T10:12:49Z (GMT). No. of bitstreams: 2 Dissertação - Gustavo de Melo Oliveira Gonçalves - 2016.pdf: 1630959 bytes, checksum: 90d5f7c22407381803a1e520c265c080 (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) Previous issue date: 2016-07-29 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / In the last years, due to the government effort, especially in the Tocantins State, there have been significante increase on flooded rice production areas. However, there are few studies about nitrogen sources and doses in that region, which could improve the nitrogen efficiency use and provide higher incomes for farmers. This study aimed to determine the effects of different sources and doses of nitrogen in flooded lowland soils in the pH, redox potential and the concentration of ions in the soil solution in order to obtain the economicallyand environmentally best mineral nitrogen source and dose. The samples were collected in the 2014/2015 season at the Embrapa Rice and Beans Experimental Field - Palmital Farm-, in a Dystric Gleysol. The design was a complete randomized blocks, with four replications, two sources of nitrogen (common urea and slow release urea), three nitrogen rates (30, 70, 150 kg ha-1), and a control, without any N application.Soil solution samples were collected weekly, during the flooded period in rice cultivation, BRS Catiana genotype. The pH analysis and Eh (redoxpotential) were immediately read, just after the soil solution sampling, in the field, and thenHCl (2M) acidified,, and immediately frozen for later analysis of the following ions: Ca, Mg, K, Fe, Zn, Mn, MOS, NO3- and NH4+. The sources used did not affect the release of nutrients dynamics to the soil solution. The anaerobic condition caused changes in the Eh and ions solubility in the soil solution. The doses applied changed Ca and MOS concentrations in solution, and the dose of 150 kg ha-1 N showed the highest values for both. / Nos últimos anos, devido incentivos do governo, especialmente no Estado do Tocantins, houve significante aumento em áreas de produção de arroz irrigado. No entanto, existem poucos estudos sobre fontes de nitrogênio e doses naquela região, o que poderia melhorar a eficiência de uso de nitrogênio e proporcionar maiores rendimentos para os produtores rurais. O presente trabalho teve como objetivo determinar os efeitos de diferentes fontes e doses de nitrogênio em solos de várzea inundados no pH, potencial redox e na concentração de íons da solução do solo, visando a obtenção da fonte e dose de fertilizante economicamente viável e ambientalmente sustentável. As amostras foram coletadas na safra 2014/2015 no Campo Experimental da Fazenda Palmital, da Embrapa Arroz e Feijão, em Gleissolo Háplico. O delineamento utilizado foi o de blocos casualizados com quatro repetições, sendo duas fontes de nitrogênio (ureia comum e ureia de liberação lenta), três doses de N aplicadas em cobertura (30, 70, 150 kg ha-1), e a testemunha absoluta, sem aplicação alguma de N. Foram coletadas amostras de solução do solo, semanalmente, durante o período de inundação no cultivo do arroz, cultivar BRS Catiana. As análises de pH e Eh (potencial de oxirredução) foram feitas logo após a coleta da solução do solo no campo, e então, acidificadas com HCl (2M), e imediatamente congeladas para posterior análise dos seguintes elementos: Ca, Mg, K, Fe, Zn, Mn, MOS, NO3- e NH4+. As fontes utilizadas não interferiram na dinâmica de liberação dos nutrientes para solução do solo. A condição de anaerobiose causou modificações no estado de oxirredução e alterou a solubilidade dos nutrientes na solução do solo. As doses aplicadas alteraram as concentrações de Ca e MOS na solução, sendo a dose de 150 kg ha-1 de N a dose que apresentou os maiores valores para ambos.

A produtividade dos plantios de eucalipto no Brasil apresentou ganhos significativos nas últimas décadas devido a avanços em melhoramento genético e silvicultura. Contudo, a produção de madeira representa apenas uma fração da produtividade primária bruta (GPP). Avaliar fluxos e partição de carbono (C) entre os diferentes componentes da floresta, e estudar o uso e a eficiência de uso dos recursos disponíveis é essencial para compreender os mecanismos que controlam a produtividade de plantios intensivamente manejados. O estudo quantificou os fluxos e partição de C e a eficiência de uso da luz para a produção de lenho (LUE) em 12 parcelas em um gradiente natural de produtividade, durante o sétimo ano de um plantio comercial de Eucalyptus grandis. Nessas mesmas parcelas, na escala da árvore, foram avaliadas a dominância do crescimento, produção de lenho e LUE, identificando a representatividade de árvores dominantes e suprimidas na produtividade do povoamento. O estudo do balanço de C e a aplicação da teoria da ecologia da produção em diferentes escalas objetivaram ampliar o conhecimento sobre os processos que governam a produtividade florestal. A heterogeneidade espacial dos atributos do solo e a topografia da área experimental influenciaram fortemente os fluxos componentes da GPP e sua partição, gerando um gradiente de produtividade. A produtividade de lenho variou de 554 gC m-2 ano-1 na parcela com menor GPP a 923 gC m-2 ano-1 na parcela com maior GPP. O fluxo de C para o solo variou de 497 gC m-2 ano-1 a 1235 gC m-2 ano-1 sem relação significativa com GPP. A partição do GPP para produção de lenho aumentou de 0,19 a 0,23, com tendência de aumento com o GPP (R2=0,30, p=0,07). A LUE aumentou em 66% (de 0,25 gC MJ-1 para 0,42 gC MJ-1) com a GPP, como resultado da elevação do fluxo e partição de C para produção de lenho. Ao longo do gradiente de produtividade, parcelas com alta eficiência quântica do dossel também mostraram alta LUE. A dominância do crescimento entre árvores teve forte impacto sobre a produtividade do povoamento. As 20% maiores árvores apresentaram em média 38% da biomassa de lenho e representaram 47% da produção de lenho. Características das folhas sugeriram que a maior produtividade de árvores dominantes, em relação às suprimidas, pode resultar de diferenças no controle estomático e não na capacidade fotossintética. A ecologia da produção na escala da árvore mostrou que os indivíduos dominantes produziram mais madeira por terem absorvido mais radiação e pela maior eficiência do uso da luz, comparativamente às árvores suprimidas. Em média, uma árvore suprimida cresceu 1,2 kg ano-1 de lenho, absorveu 2,9 GJ ano-1 de radiação e teve uma LUE de 0,4 g MJ-1. Já uma dominante cresceu 37 kg ano-1, absorveu 38 GJ ano-1 com mais que o dobro da eficiência (1,01 g MJ-1). Estudos sobre o balanço de carbono e ecologia da produção em diferentes escalas são essenciais para aperfeiçoar o conhecimento sobre os processos que controlam a produtividade de madeira e a fixação de carbono, e aprimorar os modelos ecofisiológicos. / The productivity of the eucalypt plantations in Brazil showed significant increase over the last decades, due to improvement in breeding and silviculture. However, wood production represents only a fraction of the gross primary production (GPP). Assessing carbon (C) fluxes and partitioning among forest components, and evaluate use and use efficiency of the available resources is essential to understand mechanisms driving productivity of intensively managed plantations. The study quantified fluxes and partitioning of C and light use efficiency for stem production (LUE) in 12 plots across a natural gradient of productivity during the seventh year of a commercial Eucalyptus grandis. Within these plots, at tree level, were evaluated growth dominance, stem production and LUE, identifying representativeness of dominant and suppressed trees to stand productivity. The study of C budget and the application of the production ecology theory at different levels aimed increase the knowledge about the processes driving forest productivity. The spatial heterogeneity of soil attributes and topography across the experimental site strongly influenced the component fluxes of GPP and partitioning, generating a gradient of productivity. Stem production ranged from 554 gC m-2 year-1 at the lowest GPP plot to 923 gC m-2 year-1 at the highest GPP plot. Total below ground carbon flux (TBCF) ranged from 497 g C m-2 year-1 to 1235 g C m-2 year-1, with no relationship to ANPP or GPP. Stem NPP:GPP partitioning ratio increased from 0.19 to 0.23 showing a trend of increase with GPP (R2=0.30, p=0.07). LUE increased by 66% (from 0.25 gC MJ-1 to 0.42 gC MJ-1) with GPP, as a result of the increased C partitioned and flux to stem NPP. Across the gradient of productivity, plots with the highest canopy quantum efficiency also showed the highest LUE. Growth dominance between trees showed a strong impact on stand productivity. The 20% larger trees accounted for 38% of stem biomass and represented 47% stem production. Leaf characteristics suggested that dominant trees were more productive, in relation to suppressed, may result in differences on stomatal control and not on photosynthetic capacity. The production ecology at tree level showed that dominant trees produced more wood by absorbing more radiation and due to higher light use efficiency, comparing to suppressed trees. On average, a suppressed tree grew 1,2 kg year-1 of stem, absorbed 2,9 GJ year-1 of radiation with a LUE of 0.4 g MJ-1. Although, a dominant grew 37 kg year-1 of stem, absorbed 38 GJ year-1 of radiation with the double of efficiency (1.01 g MJ-1). Studies regarding carbon balance and production ecology at different levels are essential to improve the knowledge on processes controlling wood production and carbon uptake, and develop ecophysiological models.

Fotossíntese é o processo biofísico pelo qual energia luminosa é transformada em energia química armazenada em compostos de carbono. A taxa fotossintética instantânea possui um forte padrão assintótico em resposta ao incremento da intensidade luminosa, porém quando integramos a fotossíntese em escalas espaciais e temporais maiores, observa-se um padrão linear de resposta entre radiação interceptada e produção. Esta abordagem permitiu o surgimento de modelos baseados nas taxas de conversão de energia radiante em biomassa seca, ou eficiência do uso da luz (&epsilon;). Valores publicados para o Eucalyptus estão na faixa de 0,5-2,5 g MJ-1, porém se faz necessário um entendimento mais profundo a respeito da sensibilidade destes valores às flutuações do clima e sua sazonalidade. Para isso, as taxas de crescimento, uso e eficiência do uso da luz foram monitoradas quinzenalmente durante 16 meses em parcelas de 18 clones de Eucalyptus, dos 1,3 aos 2,7 anos de idade. Foram testadas as hipóteses de que a produção de madeira aumentaria em função de incrementos no uso e/ou eficiência de uso da luz, assim como estes valores aumentariam respectivamente com incrementos no índice de área foliar e por uma alocação de carbono para o fuste, respectivamente. Os clones apresentaram uma grande amplitude de produtividade (9,9-22,7 Mg ha-1 ano-1) e arquiteturas de copa, capturando entre 65-95% da radiação incidente. Tais valores resultaram em uma eficiência do uso da luz média de 1,5 g MJ-1, variando entre 0,16-3,14 g MJ-1. Apesar de patamares distintos, os valores de eficiência de uso dos clones oscilaram de maneira similar, de modo que a radiação incidente foi a principal variável afetando a eficiência de uso da luz, estando &epsilon; positivamente relacionada a variáveis que expressam períodos de maior disponibilidade hídrica e negativamente relacionado a períodos de menor disponibilidade. Maiores valores de índice de área foliar efetivo (Le) acarretaram em maior interceptação de luz, porém as distintas arquiteturas de copa revelaram diferentes estratégias de captura de luz (0,3 < &kappa; < 0,6). Apesar de uma maior interceptação, não houve correlação significativa com a produtividade, no entanto observou-se uma forte correlação entre eficiência do uso da luz e crescimento em madeira, resultado de uma maior alocação para o fuste. Apesar de evidenciar a relação entre alocação e eficiência, existem outros mecanismos associados às alterações observadas em &epsilon; que apenas uma caracterização completa dos fluxos de carbono pode elucidar. / Photosynthesis is the biophysical process by which light energy is converted into chemical energy stored in carbon compounds. The instantaneous photosynthetic rate has a strong asymptotic pattern in response to increases in light intensity, however when we integrate photosynthesis in larger spatial and temporal scales, there is a linear pattern of response between intercepted radiation and production. This approach has allowed the appearance of models based on radiant energy conversion rates into dry biomass, or light use efficiency (&epsilon;). Published values for Eucalyptus range from 0.5 to 2.5 g MJ-1, but a deeper understanding of the sensitivity of these values to climate fluctuations and seasonality is necessary. For this reason, wood growth rates, light use and efficiency were monitored every two weeks for 16 months at 18 Eucalyptus clones plots, from 1.3 to 2.7 years of age. Our hypothesis was that wood production would be positively related to light use and efficiency, as well these values would increase respectively with increases in leaf area index and carbon allocation to the stem. Clones showed a wide range of productivity (9.9 to 22.7 Mg ha-1 yr-1) and canopy architectures, capturing between 65-95% of incident radiation. Such values resulted in an average light use efficiency of 1.8 g MJ-1, ranging from 0.16 to 3.14 g MJ-1. Although different levels, light use efficiency values for the clones fluctuated similarly. Incident radiation was the main variable affecting the efficiency of dry matter conversion, and &epsilon; values were positively related variables expressing periods of greater water availability and negatively related to periods of lower availability. Larger effective leaf area index (Le) values resulted in higher light interception, but the different canopy architectures revealed different light capture strategies (0.3 < &kappa; < 0.6). Despite a higher interception, there was no significant correlation with productivity; however there was a strong correlation between light use efficiency and wood growth, as a result of increased allocation to the stem. While evidencing the relationship between allocation and efficiency, there are other mechanisms associated with changes in &epsilon; observed that only one full characterization of the carbon fluxes can elucidate.

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.

The bulk of Zimbabwe’s groundnut (Arachis hypogaea L.) crop is grown on sandy soils in the smallholder sector where sustainable production is hindered by acid soil infertility. The study goal was thus to examine the effects of soil acidity amelioration by four Ca-containing materials on nutrient composition, vegetative and reproductive growth, and quality of groundnut to formulate ameliorative strategies to improve productivity on acid soils. The effectiveness of calcitic lime (CL), dolomitic lime (DL), gypsum (G) and single superphosphate (SSP) in ameliorating soil acidity was determined in field experiments conducted for three seasons at two Research Stations in Zimbabwe, and in greenhouse experiments conducted for two seasons at Harare Research Station. In both experiments the lime application rates were from 0 to 4000 kg ha-1, while G application rates were from 0 to 3450 kg ha-1, and those of SSP were from 0 to 250 kg ha-1. Calcitic or dolomitic lime applied at 2000 or 4000 kg ha-1 increased soil pH and Ca and Mg contents in the pod and root zones, and in the plant material. Gypsum and SSP applications at 200 and 250 kg ha-1 respectively, had no significant effects on pH, Ca and Mg levels, but when applied in equivalent amounts of Ca as lime, gypsum improved soil Ca status. Effects of the four ameliorants on the N, P and K levels in the soils and in plant material were generally neither significant nor consistent. The direct and residual benefits of application of CL or DL were manifested in improved plant stands, better growth, nodulation, productivity and quality of groundnut. Gypsum applied at equal Ca rates as CL or DL was the superior Ca-source in improving pod and kernel quality. By the end of the third season, the increases in cumulative kernel yields due to application of 4000 kg ha-1 lime over non-application were up to 319%. The major growth-limiting factors on the studied acid soils were identified as deficiencies of Ca and Mg, and low pH per se. In a field experiment conducted to evaluate the tolerance of 15 groundnut genotypes to soil acidity, significant differences in yield and nutrient utilization efficiency of the genotypes were observed, implying that productivity on acid soils can be increased by growing genotypes efficient in uptake and utilization of nutrients. Results from greenhouse and growth chamber studies conducted to examine the effects of pH (3.0 - 7.0) and its interactions with Ca (0 - 2000 µM Ca) on early seedling growth and reproductive growth of groundnut indicated that low pH per se has a major detrimental impact on seedling survival, growth, pod formation, yield and quality of groundnut, but not on germination. The adverse effects of low pH were more pronounced in the absence of Ca, and became progressively less as the solution Ca concentrations increased. Further experiments showed that it is feasible to mitigate the adverse effects of soil acidity on groundnut germination and seedling survival by pelleting seeds with small amounts of CaCO3, or priming with CaSO4. / Dissertation (PhD (Plant Production: Agronomy))--University of Pretoria, 2003. / Plant Production and Soil Science / unrestricted

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

<p>Wheat is a major source of calories and protein for humans worldwide. Wheat is the most widely grown crop, with cultivation areas and production systems on every continent. The cultivated land area is vast because of its importance and adaptability to various environmental conditions. Global wheat production has not kept up with the growing population, provoking the need to develop new methods and techniques to increase genetic gains. The first research chapter of this Ph.D. dissertation involves performing genome-wide association studies (GWAS) to identify and examine transferability of marker-trait associations (MTAs) across environments. I evaluated yield and yield components traits among 270 soft red winter (SRW) wheat varieties. The population consists of experimental breeding lines adapted to the Midwestern and eastern United States and developed by public university breeding programs. Phenotypic data from a two-year field study and a 45K-SNP marker dataset were analyzed by FarmCPU model to identify MTAs for yield related traits. Grain yield was positively correlated with thousand kernel weight, biomass, and grain weight per spike while negatively correlated with days to heading and maturity. Sixty-one independent loci were identified for agronomic traits, including a region that with <i>–logP</i> of 16.35, which explained 18% of the variation in grain yield. Using 12 existing datasets from other states and seasons, in addition to my own data, I examined the transferability of significant MTAs for grain yield and days to heading across homogenous environments. For grain yield and days to heading, I only observed 6 out of 28 MTAs to hold up across homogenous environments. I concluded that not all marker-trait associations can be detected in other environments.</p><p>In the second research chapter of this Ph.D. dissertation, I dissected yield component traits under contrasting nitrogen environments by using field-based low-throughput phenotyping. I characterized grain yield formation and quality attributes in soft red winter wheat. Using a split-block design, I studied responses of 30 experimental lines, as sub-plot, to high nitrogen and low nitrogen environment, as main-plot, for two years. Differential N environments were imposed by the application, or lack thereof, of spring nitrogen application in a field, following a previous corn harvest. In this study, I measured agronomic traits, in-tissue nitrogen concentrations, nitrogen use efficiency, nitrogen harvest index and end-use quality traits on either all or subset of the germplasm. My data showed that biomass, number of spikes and total grain numbers per unit area were most sensitive to low nitrogen while kernel weight remained stable across environments. Significant genotype x N-environment interaction allowed me to select N-efficient germplasm, that can be used as founding parents for a potential breeding population specifically for low-N environments. I did this selection on the basis of superior agronomic traits and the presence of the desirable gluten quality alleles such as <i>Glu-A1b </i>(<i>2*</i>) and <i>Glu-D1d </i>(<i>5+10</i>).</p>

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