As mudanças climáticas globais e a expansão da cultura da cana-de-açúcar para regiões com menor suprimento hídrico elevaram a importância de estimativas consistentes das necessidades de água da cultura. Na tentativa de contribuir nesse campo, o presente trabalho buscou analisar o consumo hídrico da cana-de-açúcar em três diferentes escalas espaciais: folha, planta e dossel, além de uma ferramenta de simulação (DSSAT/CANEGRO) quanto ao seu desempenho na estimativa do consumo hídrico da cana-de-açúcar. Foram realizadas medidas de evapotranspiração do dossel pelo método do balanço de energia-razão de Bowen (MRB) e de transpiração das plantas por meio do balanço de calor nos colmos (BC) e das folhas com um analisador de gás à infravermelho (IRGA). Duas áreas experimentais foram utilizadas, sendo a primeira com a variedade CTC 12, na safra 2011/2012, irrigada por gotejamento subsuperficial; a segunda área com a variedade RB867515, irrigada por aspersão por meio de um pivô central, na safra 2012/2013. O acoplamento planta-atmosfera também foi avaliado. As análises do MRB indicaram um fluxo de calor latente médio de 70% da energia disponível no ambiente, com 25% de fluxo de calor sensível e 5% no fluxo de calor no solo. Com a mesma metodologia a evapotranspiração da cultura média (ETc) foi estimada em 3,92 e 3,25 mm dia-1 para as variedades CTC 12 e RB867515, respectivamente, resultando em um coeficiente de cultura (Kc) médio de 1,37, na fase de pleno desenvolvimento vegetativo. No período experimental, o canavial permaneceu mais acoplado à atmosfera (Ω médio=0,37) e a transpiração avaliada pelo BC chegou a 4,7 e 3,62 mm dia-1, respectivamente para CTC 12 e RB867515. A metodologia do IRGA resultou em perda de água ao nível foliar da faixa de até 1 mm h-1. Conforme a demanda atmosférica, o Kc da cultura apresentou-se variável em função da evapotranspiração de referência (ETo). O modelo DSSAT/CANEGRO mostrou-se eficiente na simulação da ETc e transpiração do canavial, com resultados mais satisfatórios (R2=0,59) quando utiliza-se a metodologia FAO 56 nas simulações. / Global climate change and the sugarcane crop expansion to regions with lower water supply became more important the real estimate of crop water requirements. This study aimed to contribute on this regard by analyzing the sugarcane water consumption at three different spatial scales: leaf, plant and canopy. The DSSAT/CANEGRO crop model was also evaluated with respect to sugarcane transpiration and evapotranspiration. Bowen ratio energy balance (BREB) method was performed to measure crop canopy evapotranspiration and the transpiration were measured with sap flow by stem heat balance for plant scale and infra-red gas analyzer (IRGA) for leaf scale. Two experimental sites were used: the first with CTC 12 cultivar and drip irrigation, on 2011/2012 season; in the second experiment the RB867515 variety was grown under sprinkler irrigation by a central pivot, on the 2012/2013 growing season. The plant-atmosphere decoupling factor was also evaluated. BREB method showed latent heat flux representing 70% of the available energy, 25% for sensible heat flux, and 5% for soil heat flux. BREB crop evapotranspiration (ETc) ranged from 3.92 to 3.25 mm day-1 for CTC 12 and RB867515, respectively, resulting in a mean crop coefficient (Kc) of 1.37 at the full vegetative growth stage. In the experimental period, sugarcane crop was coupled to the atmosphere (Ω=0.37) and transpiration assessed by HB reached 4.7 and 3.62 mm day-1 for CTC 12 and RB867515, respectively. IRGA method showed a leaf water loss up to 1 mm h-1. Kc varied with reference evapotranspiration (ETo) The DSSAT/CANEGRO crop model was efficient in the ETc and transpiration simulation, with better results (R2=0.59) when using FAO 56 ETo method in the simulations.

L’anticipation des effets des changements climatiques nécessite une bonne compréhension dufonctionnement carboné des écosystèmes continentaux. L’une des principales contraintes liées àl’étude de ces écosystèmes est la forte variabilité à la fois spatiale et temporelle de leurs flux decarbone et de leurs réponses aux contraintes abiotiques. L’usage de méthodes de télédétectionoptiques pourrait permettre de suivre de façon spatialisée le fonctionnement des couverts végétaux.Ce travail vise à évaluer le potentiel de méthodes de télédétection pour décrire la structure et lefonctionnement de couverts végétaux à des échelles spatiales et temporelles variées. Pour ce faire,les relations entre indices optiques et phénomènes biologiques ont été étudiées en suivant unedémarche de transfert d’échelle, des échelles les plus fines aux plus larges. Il a été montré que le PRI(Photochemical Reflectance Index), utilisé en tant qu’indicateur du LUE (Light Use Efficiency), est parnature un signal composite qui reflète principalement la régulation du rendement de laphotosynthèse sur des échelles de temps fines, et la structure et composition biochimique ducouvert à l’échelle de la saison. L’analyse de courbes de réponse du PRI au PAR (PhotosyntheticallyActive Radiation) a permis de déconvoluer ces deux sources de variabilité, via l’introduction duconcept de PRI0 ou PRI d’une feuille idéalement adaptée à l’obscurité. Ce PRI0, capturant la variabilitédu PRI indépendante du LUE, a pu être mesuré à l’échelle de la feuille, et estimé à l’échelle de jeunescouverts végétaux et de la parcelle. Cette variabilité a pu être expliquée à l’échelle de la feuille et dejeunes couverts végétaux par les variations du contenu en pigment des feuilles. A l’échelle depeuplements adultes et de l’année, elle résulte cependant d’effets combinés de la compositionbiochimique et de la structure des couverts qui n’ont pu être séparés. Ces effets sont susceptiblesaux échelles larges de masquer en bonne partie, voire de biaiser la relation entre PRI et LUE. Il a enoutre été montré que la représentativité du PRI est limitée aux strates supérieures des canopées etdépend de la structure du couvert et du climat lumineux, ce qui peut limiter son intérêt en tantqu’estimateur du LUE à l’échelle de l’écosystème. Ces résultats soulignent la nécessité de prendre encompte la structure et la composition biochimique des couverts végétaux dans le cadre d’uneutilisation du PRI en tant que proxy du LUE de l’écosystème. / In order to assess the effect of global warming, a good understanding of carbon functioning ofterrestrial ecosystems is needed. The study of terrestrial ecosystem carbon fluxes and responses toabiotic stress remain challenging due to their high spatial and temporal variability. The use of remotesensing may help us to describe those sources of variability. The aim of this work is to assess thepotential of remote sensing as a way to describe canopy structure and functioning over a broadrange of temporal and spatial scales. The relationships between optical indices and biologicalphenomenon were investigated over a range of increasing scales. The PRI (PhotochemicalReflectance Index), used as a proxy of the LUE (Light Use Efficiency) was shown to be a compositesignal, mainly impacted by the regulation of the LUE at short time scales, and by canopy structureand pigment content at seasonal scale. The analysis of PRI response to PAR (PhotosyntheticallyActive Radiation) allowed us to deconvolve those two sources of variability thanks to theintroduction of the PRI0 defined as the PRI of ideally dark adapted leaves. The PRI0 was shown toefficiently describe the LUE unrelated PRI variability, and could be measured at leaf scale, andestimated at the leaf, canopy and stand scales. This variability could be explained by changes in leafpigment content over the growing season at leaf and canopy scales. At the stand scale and over theyear, this LUE independent PRI variability resulted from combined effects of canopy structure andpigment content, which could not be separated. These effects may result in biased or masked PRIversus LUE relationships at larges scales. Moreover, it was shown that the in-situ PRI measurementsmainly responded to the LUE of sunlit leaves, depending on canopy structure and sky conditions. Thismay considerably hamper the use of the PRI as a proxy of the whole ecosystem LUE. These resultsillustrate the need to take canopy structure and pigment content into account while using the PRI asa proxy of the ecosystem LUE.

Submitted by Celso Magalhaes (celsomagalhaes@ufrrj.br) on 2018-08-02T15:53:51Z No. of bitstreams: 1 2017 - Ana Carolina Mendes Bezerra.pdf: 1946898 bytes, checksum: 5eac08b2a62141f12ea8b97452156ae3 (MD5) / Made available in DSpace on 2018-08-02T15:53:54Z (GMT). No. of bitstreams: 1 2017 - Ana Carolina Mendes Bezerra.pdf: 1946898 bytes, checksum: 5eac08b2a62141f12ea8b97452156ae3 (MD5) Previous issue date: 2017-02-16 / Irrigation acts as an important factor to reduce risks and increase productivity in agricultural crops. However, due to increasing water scarcity and the waste of water practiced by many farmers, there is great concern about the negative impacts of this technique on the productive sector, generating the need to establish a balance between agricultural productivity and the preservation of natural resources. In this scenario, studies related to water economics are inserted through more sustainable types of irrigation management. The objective of this study was use the Simplified Irrigation Controller sensor positioned in the atmosphere, to control the irrigation of lettuce seedlings based on the variation of water vapor pressure. The performance of the adaptation was evaluated by monitoring plant parameters, as well as, water use efficiency (WUE). The device was evaluated with the ceramic sensor positioned outside the substrate, in the atmosphere adjacent to the production trays, seeking to correlate the applied water with the vapor pressure deficit (VPD) observed at the experiment site. The seeds of the Regina cultivar were sown in polystyrene trays (200 cells) with substrate used in organic cultivation. A randomized block design was used in a factorial scheme where factor A were four adjustments of the SIC (3.5; 5, 6.5 and 8kPa) and factor B were the two evaluation periods (from July 8 to August 8 and September 16 to October 16, both in 2016) with four replications, totaling 32 plots (experimental units). Parameters related to the growth and physiology of the crop was evaluated, such as: fresh mass, dry mass, water use efficiency, chlorophyll fluorescence parameters and stomatal conductance. The results were submitted to analysis of variance and in the presence of significant interaction a Sliced- analysis was carried out for each factor. Scott-Knott test was used to determine significance with the cut off at 5%.Biometric and physiological variables tested showed a decrease as the tested tensions were increased. The 3.5 kPa tension showed a higher potential for producing more vigorous seedlings, presenting WUE with an average value of 1.37 g L-1 and producing a seedling with approximately 32.4 mL of water in the second experimental period. The cultivation of lettuce seedlings is possible in both experimental periods. The results show the availability of the use of the SIC with atmospheric sensor and compatibility of the applied water volume applied with the observed VPD / A irriga??o atua como importante fator de redu??o de risco e incremento na produ??o de culturas agr?colas. Por?m, devido ? crescente escassez h?drica e ao desperd?cio de ?gua praticado por grande parte dos agricultores, h? uma grande preocupa??o em rela??o aos impactos negativos dessa t?cnica, gerando a necessidade de se estabelecer um equil?brio entre a produtividade agr?cola e a preserva??o dos recursos naturais. Nesse cen?rio se inserem estudos relacionados com efici?ncia h?drica por meio de tipos de manejo da irriga??o mais sustent?veis. O objetivo desse estudo foi utilizar o sensor do Acionador Simplificado de Irriga??o (ASI) na atmosfera para controlar a irriga??o de mudas de alface baseando-se na varia??o de press?o de vapor da ?gua. O desempenho da adapta??o foi avaliado por meio do monitoramento de par?metros na planta, bem como, da efici?ncia de uso da ?gua (EUA). O acionador foi avaliado com o sensor cer?mico posicionado fora do substrato, na atmosfera adjacente superior as bandejas de produ??o, buscando correlacionar a ?gua aplicada com o d?ficit de press?o de vapor observado nesse local. As sementes da cultivar Regina foram semeadas em bandejas de isopor (200 c?lulas) com substrato utilizado em cultivo org?nico. Foi utilizado o delineamento experimental de blocos casualizados, em esquema fatorial, onde o fator A foi quatro regulagens do acionador (3,5; 5; 6,5 e 8 kPa) e o fator B as duas ?pocas de avalia??o (de 8 de julho a 8 de agosto e 16 de setembro ? 16 de outubro, ambas no ano de 2016), com quatro repeti??es, totalizando 32 parcelas. Foram avaliados par?metros referentes ao crescimento e fisiologia da cultura, quais sejam: massa fresca, massa seca, par?metros de cin?tica da fluoresc?ncia da clorofila a e condut?ncia estom?tica, al?m da EUA. Os resultados foram submetidos ? an?lise de vari?ncia e na presen?a de intera??o significativa foi realizada nova an?lise de vari?ncia com desdobramento dos graus de liberdade. Teste de Scott-Knott foi usado para determina??o de signific?ncia a 5% de probabilidade. As vari?veis biom?tricas e fisiol?gicas avaliadas apresentaram decr?scimo conforme foram aumentadas as tens?es de acionamento. A tens?o 3,5 kPa mostrou maior potencial para produ??o de mudas mais vigorosas, apresentando EUA com valor m?dio de 1,37 g L-1 e produzindo uma muda com aproximadamente 32,4 mL de ?gua na segunda ?poca experimental. O cultivo de mudas de alface mostra-se poss?vel nas duas ?pocas experimentais. Os resultados mostram a viabilidade do uso do acionador com sensor atmosf?rico e compatibilidade do volume de ?gua aplicado com o d?ficit de press?o de vapor da atmosfera observado.

Thesis (M.Sc.(Agronomy)) --University of Limpopo, 2015 / The changes in climate, especially poor rainfall patterns and distributions are key issues posing major agricultural challenges for food security and threaten the rural livelihoods of many communities in the Limpopo Province. Rainfall (P) is low and limited. These limited P is mostly lost through runoff and evaporation, which result in low soil moisture availability and possible crop failure. Therefore, techniques that reduce these water losses are important for improving dryland crop production and rainwater productivity (RWP). The objectives of this study were to determine the potential and effectiveness of rainwater harvesting and conservation techniques (RWH&CT’s) to conserve and improve plant available water (PAW) for dryland maize production and also determine the efficiency of the RWH&CT’s to improve dryland maize yield and RWP compared to conventional tillage (CON). The study was conducted over a period of two growing seasons (2008/09; 2009/10) using maize as indicator crop at the Towoomba Research Station of the Limpopo Department of Agriculture in the Limpopo Province of South Africa, on an Arcadia ecotope. The experiment was laid out in a randomized complete block design, with four replications and five treatments. The five treatments used in the study were; conventional tillage (CON), No-till (NT), In-field rainwater harvesting (IRWH), Mechanized basins (MB) and Daling plough (DAL). The IRWH and DL were classified as rainwater harvesting techniques (RWHT’s), whilst MB and NT were classified as water conservation techniques. Two access tubes were installed at each treatment to measure the soil water content (SWC) at four different soil depths of 150, 450, 750 and 1050 mm using the neutron water meter. The data collected included climatic data, soil and plant parameters. The data were subjected to analysis of variance through NCSS 2000 Statistical System for Windows and GENSTAT 14th edition. Mean separation tests were computed using Fisher's protected least significant difference test. The SWC of IRWH, DAL and MB were about 510 and 490 mm higher compared to CON and NT treatment during the 2008/09 and 2009/10 seasons, respectively. The PAWT of the IRWH, MB and DAL was significantly different from the CON treatment during the 2008/09 season. For both seasons the biomass yield of the IRWH treatment was significantly different from the NT treatment, producing 23 and 50% more biomass in the 2008/09 and 2009/10 growing seasons, respectively. The grain yield under IRWH was significantly different from the NT treatment during both 2008/09 and 2009/10 seasons. The highest maize grain yield of IRWH was achieved during the 2009/10 season with 56% higher grain yield than the NT treatment. RWP from various RWHT’s were significantly different from the NT treatment. These results indicate that IRWH and DAL were 12 and 2% more effective in converting rainwater into harvestable grain yield than the CON treatment. R2 values of 68.6 and 78.4% for SWC and transpiration (Ev) were obtained when correlated with maize grain yield respectively. This indicates the importance of moisture conservation for improved dryland maize production under low P areas. Therefore, the use of appropriate RWHT’s by smallscale farmers maybe crucial to improve dryland maize production. IRWH outperformed all other treatments in terms of the soil parameters and plant parameter measured during the period of this study. Therefore, these results suggest IRWH has potential of sustaining maize yields under low rainfall conditions. Key words: Rainwater harvesting, conservation techniques, ecotope, rainwater productivity, maize yield, precipitation use efficiency.

This research examined the mechanisms by which temperature, water availability and nitrogen (N) affect the dry matter (DM) yield potential of cocksfoot (Dactylis glomerata L.) dominant pastures. The experiment was a split plot design with main plots of fully irrigated (I) or dryland (D), sub-plots of N fertiliser at 800 kg N/ha in 2003/04; and 1600 kg N/ha in 2004/05 (+N) or 0 kg N/ha (-N). The potential environmental yield of an established 8 year old cocksfoot dominant pasture was 21.9 t DM/ha/y from I+N pastures compared with 9.8 t DM/ha by I-N pastures and 15.1 t DM/ha/y by D+N pastures. The lowest yields were from dryland pastures with no N which produced 7.5 t DM/ha/y in 2003/03 and 5.0 t DM/ha/y in 2004/05. The effect of seasonal temperatures on the DM production, when periods of water stress were excluded, was quantified using thermal time accumulated above a base temperature of 3°C as 7.0 kg DM/°Cd/ha for N fertilised pastures and 3.3 kg DM/°Cd/ha for pastures with no N. The 2.5 t DM/ha difference in yields of D-N pastures in 2003/04 and 2004/05 was the result of the duration, extent and timing of the water stress period. In both years the critical limiting deficit (DL) was calculated as 78 mm from the soil moisture deficit in the 0-0.8 m soil layers. Beyond DL yield decreased at a rate of 1.45%/mm in +N and –N pastures, relative to fully irrigated control pastures. Yields of D+N and D-N pastures were similar during periods of water stress with 0.4±0.1 t/DM/ha produced during the rotation ending 30/12/2003. This was less than from either the I-N (1.2 t DM/ha) or I+N (3.5 t DM/ha) pastures due to the reduction in the amount of photosynthetically active radiation intercepted by the canopies of the dryland pastures. However, in the rotation ending 2/5/2004, after autumn rain alleviated drought conditions, yield of the D+N pasture was 2.1 t DM/ha compared with 1.7 t DM/ha by I+N pastures. The effect of N on yield was described using a nutrition index which showed that as DM yield increased N% in the herbage declined. This is a function of the ratio between metabolic and structural N requirements rather than caused by ontogeny alone. Specific leaf N was determined at two harvests and appeared constant at a given point in time (1.0-1.6 g N/m² leaf). In contrast, specific pseudostem N increased from 0.8-1.0 g N/m² pseudostem at an NNI of 0.4 in –N pastures to 2.6-3.0 g N/m² pseudostem at an NNI of 1.2 in the +N pastures. Differences between the yields of +N and –N pastures were caused by differences in radiation use efficiency (RUE) as determined by the linear relationship (R²=0.76) between RUE and the nitrogen nutrition index (NNI). In this thesis, empirical relationships for the effects of temperature, water availability and N were derived and the physiological mechanisms which underlie these descriptions were identified. These relationships provide clear and simple explanations of the effects of environmental variables on the productivity of cocksfoot based pastures which will enhance understanding of the benefits and limitations of cocksfoot, particularly in dryland farming systems.

As nitrogen (N) is a critical nutrient for plant growth, the development of synthetic N fertilisers dramatically changed agricultural production in the twentieth century. Improvement in N use efficiency (NUE) has been a focus of breeding for grain crop species, since protein is an important component of the harvested product. The study of NUE in sugarcane has lagged behind grain crops, mainly because N is not a component of sucrose, the primary product of the traditional sugarcane industry. Recently, improvement in NUE has become a focus of sugarcane breeding, due largely to environmental concerns regarding pollution from high N fertilisation, and the increasing cost of N fertilisers. This thesis aimed to gain an initial understanding of the genetic basis for variability in NUE in sugarcane. This was achieved through: (i) the screening of 168 sugarcane genotypes under limiting and non-limiting N supply in two glasshouse experiments; (ii) the mapping of marker-trait associations (MTA) for biomass and physiological traits under limiting and non-limiting N supply in a sugarcane mapping population; (iii) the analysis of expression of candidate genes encoding enzymes involved in the central processes of N assimilation and remobilisation in plants; and (iv) the mapping of candidate genes in a sugarcane genetic map. Genetic variation was identified for growth traits as well as physiological traits including %N, internal NUE (iNUE, g dry weight g-1 N) and leaf glutamine synthetase (GS) activity in a sugarcane mapping population. These traits were also analysed for linkage with genetic markers. Genetic variation in the screened genotypes was higher under limiting N supply, a finding that was reflected by the fact that marker-trait associations (MTA) for increases in iNUE were not identified under non-limiting N supply in the commercial parent of the mapping population. Contrary to findings in grain crop species, there was no link between GS activity and other traits, either through phenotypic correlations or co-location of MTA. The expression of candidate genes encoding GS, nitrate reductase (NR) and alanine amintotransferase (AlaAT) was quantified with Sequenom™ MassARRAY technology. Plants were grown under growth-limiting N supply, non-limiting N supply, or a N-pulse treatment, which consisted of growth-limiting N supply followed by non-limiting N supply 24 hours prior to sampling. Two genes, scAlaAT.d and scGS1.a, encoding AlaAT and GS respectively, were identified as non-responsive to changes in N supply, whereas scAlaAT.a, scGS1.b and scGS1.c had significantly (p<0.05) increased expression under a N-pulse, indicating an important role for these genes in the response of sugarcane to a sudden increase in N availability. The location of candidate genes associated with variation in NUE in a sugarcane genetic map were sought through restriction fragment length polymorphism (RFLP) markers. Twenty-two probes were screened, of which two generated single-dose markers, allowing the mapping of a single allele of scAspAT, encoding aspartate aminotransferase, and two alleles of scGS2, encoding plastidic GS. Because of the economic and environmental consequences of inefficient N fertiliser application, the development of sugarcane cultivars with improved NUE is essential. Since variation for NUE exists, especially in unimproved sugarcane varieties, this may be achieved through traditional breeding methods by screening existing breeding populations under limiting N supply. Additionally, an improved understanding of the genetic basis of variation for NUE in sugarcane should be pursued by further analysis of candidate gene response to changing N availability by screening widely varying cane species for differences in gene expression, enzyme activity and metabolite profiles. The further addition of candidate gene locations to sugarcane genetic maps will aid both future marker-assisted selection in breeding, and a fundamental understanding of genetic control of NUE variation. Through the development of sugarcane cultivars with improved NUE and an enhanced knowledge of the genetic control underpinning sugarcane N physiology, concerns regarding high N fertiliser applications may be mitigated and sustainability ensured.

The urban water demand in Southwest Texas has grown rapidly in recent years due to the population increases in urban areas, which caused conflict between municipal and agricultural water use. Deficit irrigation is one important measure for solving this problem. A field experiment with seven different irrigation treatments and four cotton varieties was conducted at the Texas AgriLife Research and Extension Center at Uvalde in the summers of 2008 and 2009 to examine the water saving potential and related phenological/physiological responses in Southwest Texas. The results showed that: 1) The threshold deficit ratio for a traditional deficit irrigation scheme falls between 0.7 and 0.8 for cotton production in Southwest Texas under a low energy precision application (LEPA) sprinkler irrigation system. The 70 percent evapotranspiration (ET)-initialled regulated deficit irrigation scheme (70R) performed well in maintaining lint yield in most cotton varieties tested. The significant changes detected in lint quality failed to introduce premiums or discounts in cotton price. 2) The phenological parameters (plant height, node number and flower/fruit number) showed clear trends that illustrate the relationship between increased stress level and decreased plant growth and development. The observed inconsistency of the physiological responses in the two growing seasons may imply that physiological parameters are not good direct predictors of lint yield if measurements are conducted only on a point basis. The partitioning coefficients of boll dry weight in both years failed to show a significant difference between deficit irrigation treatments and the control, indicating that reallocation of carbohydrates may not be the major factor of maintaining lint yield for the deficit irrigation treatments. 3) Economic analysis showed that due to the low water price, it is not currently profitable to adopt deficit irrigation. In case that water price is increased, it may become more profitable to adopt deficit irrigation. This work provides reference information to water authorities and policy makers to set quotas for municipal and agricultural water use and to value water properly through setting different water prices.

As a result of predicted climate change, environmental conditions may make woody plant species such as poplars (Populus spp.) vulnerable unless they are sufficiently adaptable to the new environment. This greenhouse study examined the responses of Hill, Northwest, Okanese and Walker hybrid poplar clones to drought, a potential outcome of a changing climate. Plants were grown from cuttings and subjected to two soil moisture treatments; a well-watered treatment and a drought conditioning treatment in which plants were subjected to cycles of soil moisture deficit. The first study examined growth and gas exchange following treatments, while the second study examined concurrent changes in leaf water potential and gas exchange during a period of increasing soil moisture deficit, following treatments.<p> Hill and Okanese plants had reduced shoot:root ratios, possibly leading to more positive plant moisture balances compared to Northwest and Walker plants. Stomatal characteristics related to steady state gas exchange with Okanese plants having stomata predominantly on lower leaf surfaces, and lower stomatal conductance and Northwest plants having relatively large stomata and increased stomatal conductance. Hill and Okanese plants had the most responsive stomata, which began to close at much higher levels of leaf water potential (-0.45 and -0.54 MPa) than Northwest or Walker plants (-1.03 and -0.88 MPa); however, closure was more gradual in Okanese plants. Drought preconditioning resulted in stomatal closure occurring at higher leaf water potentials in droughted Northwest and Walker plants compared to well-watered plants. Regardless of soil moisture treatment, WUE was highest in Okanese and Walker plants. The drought treatment did however lead to increased WUE in Hill and Northwest plants.<p> Overall, Okanese plants appear to be the best adapted to conditions of reduced soil moisture based on growth and physiological traits, while Northwest and Hill seem better suited to areas where moisture deficits are likely to be less frequent or less severe. Results indicate that variability exists in adaptability of hybrid poplar clones to drought, suggesting that there may also be other hybrid clones that are adaptable to reduced soil moisture conditions, which may merit further investigation.

The feasibility of using optical sensors and non-nitrogen limiting reference crops to determine post-emergent nitrogen fertilizer requirements of canola was evaluated. Normalized difference vegetation index was well suited for estimating yield potential and nitrogen status. Although sensor-based nitrogen management was generally agronomically feasible for canola, the economic benefits of doing so remain uncertain because of the added cost of applying post-emergent nitrogen. / February 2008

As a result of predicted climate change, environmental conditions may make woody plant species such as poplars (Populus spp.) vulnerable unless they are sufficiently adaptable to the new environment. This greenhouse study examined the responses of Hill, Northwest, Okanese and Walker hybrid poplar clones to drought, a potential outcome of a changing climate. Plants were grown from cuttings and subjected to two soil moisture treatments; a well-watered treatment and a drought conditioning treatment in which plants were subjected to cycles of soil moisture deficit. The first study examined growth and gas exchange following treatments, while the second study examined concurrent changes in leaf water potential and gas exchange during a period of increasing soil moisture deficit, following treatments.<p> Hill and Okanese plants had reduced shoot:root ratios, possibly leading to more positive plant moisture balances compared to Northwest and Walker plants. Stomatal characteristics related to steady state gas exchange with Okanese plants having stomata predominantly on lower leaf surfaces, and lower stomatal conductance and Northwest plants having relatively large stomata and increased stomatal conductance. Hill and Okanese plants had the most responsive stomata, which began to close at much higher levels of leaf water potential (-0.45 and -0.54 MPa) than Northwest or Walker plants (-1.03 and -0.88 MPa); however, closure was more gradual in Okanese plants. Drought preconditioning resulted in stomatal closure occurring at higher leaf water potentials in droughted Northwest and Walker plants compared to well-watered plants. Regardless of soil moisture treatment, WUE was highest in Okanese and Walker plants. The drought treatment did however lead to increased WUE in Hill and Northwest plants.<p> Overall, Okanese plants appear to be the best adapted to conditions of reduced soil moisture based on growth and physiological traits, while Northwest and Hill seem better suited to areas where moisture deficits are likely to be less frequent or less severe. Results indicate that variability exists in adaptability of hybrid poplar clones to drought, suggesting that there may also be other hybrid clones that are adaptable to reduced soil moisture conditions, which may merit further investigation.