Carbon dioxide efflux rates (CER) of stems and roots of overstory and understory black cherry (<i>Prunus serotina</i> Ehrh., BC), red maple (<i>Acer rubrum</i> L., RM) and northern red oak (<i>Quercus rubra</i> L., RO) trees were monitored over two growing seasons at two contrasting sites in the Great Smoky Mountains to investigate diurnal and seasonal patterns in respiration and to develop prediction models based on environmental and plant parameters. CER of small roots (d<0-8 mm) was measured with a newly developed system which allows periodic <i>in situ</i> measurements by using permanently installed flexible cuvettes. Temperature-adjusted CER of roots showed no diel variation. The moderate long-term changes occurred simultaneously in all species and size classes, suggesting that they were driven mostly by environmental factors. Mean root CER ranged from 0.5 to 4.0 nmol g⁻¹ d.w. s⁻¹. Rates were up to six times higher for fine roots (d<2.0 mm) than for coarse roots. CER (per unit length) of boles (d>10 cm) and twigs (d<2 cm) was related to diameter by the function lnCER = a+<i>D</i>·lnd, with <i>D</i> between 1.2 and 1.8. A new, scale-invariant measure of CER, based on <i>D</i>, facilitated comparisons across diameters. Q₁₀ varied with the method of determination, and it was higher in spring (1.8-2.5) than in autumn (1.4-1.5) for all species. Daytime bole CER often fell below temperature-based predictions, likely due to transpiration. The reduction (usually <10%) was less pronounced at the drier site. Twig CER showed more substantial (often >±50%) deviations from the predictions. Deviations were higher in the canopy than in the understory. Mean bole maintenance respiration (at 20°C and d=20 cm) was 0.66, 0.43 and 0.50 μMol m⁻¹, while the volume-based growth coefficient was around 5, 6 and 8 mol cm⁻³ for BC, RM and RO, respectively. In a controlled study, BC and RM seedlings were fumigated in open-top chambers with sub-ambient, ambient and twice-ambient levels of ozone. The twice-ambient treatment reduced stem CER in BC by 50% (p=0.05) in July, but there was no treatment effect in September or in RM. Ozone reduced root/shoot ratio and diameter growth in BC, and P_max in both species. / Ph. D.

Mountain meadows in the western USA are experiencing increased rates of conifer encroachment due to climate change and land management practices. Past research has focused on conifer removal as a meadow restoration strategy, but there has been limited work on conifer transpiration in a pre-restoration state. Meadow restoration by conifer removal has the primary goal of recovering sufficient growing season soil moisture necessary for endemic, herbaceous meadow vegetation. Therefore, conifer water use represents an important hydrologic output toward evaluating the efficacy of this active management approach. This study quantified and evaluated transpiration of encroached conifers in a mountain meadow using sap flow prior to restoration by tree removal. We report results of lodgepole pine transpiration estimates for an approximate 1-year period and an evaluation of key environmental variables influencing water use during a dry growing season. The study was conducted at Rock Creek Meadow (RCM) in the southern Cascade Range near Chester, CA, USA. Sap flow data were collected in a sample of lodgepole pine and scaled on a per-plot basis to the larger meadow using tree survey data within a stratified random sampling design (simple scaling). These estimates were compared to a MODIS evapotranspiration (ET) estimate for the meadow. The 1-year period for transpiration estimates overlapped each of the 2019 and 2020 growing seasons partially. The response of lodgepole pine transpiration to solar radiation, air temperature, vapor pressure deficit, and volumetric soil water content was investigated by calibrating a modified Jarvis-Stewart (MJS) model to hourly sap flow data collected during the 2020 growing season, which experienced below average antecedent winter precipitation. The model was validated using spatially different sap flow data in the meadow from the 2021 growing season, also part of a dry year. Calibration and validation were completed using a MCMC approach via the DREAM(ZS) algorithm and a generalized likelihood (GL) function, enabling model parameter and total uncertainty assessment. We also used the model to inform transpiration scaling for the calibration period in select plots in the meadow, which allowed comparison with simple scaling transpiration estimates. Average total lodgepole pine transpiration at RCM was estimated between 220.57 ± 25.28 and 393.39 ± 45.65 mm for the entire campaign (mid-July 2019 to mid-August 2020) and between 100.22 ± 11.49 and 178.75 ± 20.74 mm for the 2020 partial growing season (April to mid-August). The magnitude and seasonal timing were similar to MODIS ET. The model showed good agreement between observed and predicted sap velocity for the 2020 partial growing season (RMSE = 1.25 cm h-1), with meteorological variables modulating early growing season sap flow and volumetric soil water content decline imposing transpiration decrease in the late growing season. The model validation performed similarly to calibration in terms of performance metrics and the influence of meteorological variables. The consistency of the declining volumetric soil water content effect during the late growing season between periods could not be evaluated due to an abridged validation period. Overall, the implementation GL-DREAM(ZS) showed promise for future use in MJS models. Lastly, the model derived transpiration estimates for the 2020 partial growing season showed some of the potential utility in using the MJS model to scale sap flow at the study locale. It also highlights some of the key limitations of this approach as it is executed in the present study.

A citricultura é um setor de grande importância para o país na geração de divisas, formação de renda e capital. Um dos fatores críticos no sucesso de um sistema de irrigação localizada é a definição em projeto da fração de área molhada no solo. Face às dificuldades técnicas encontradas nesse tipo de estudo, até o presente, inexistem na literatura científica trabalhos confiáveis que estabeleçam os valores ótimos de fração de área molhada no solo para as diferentes culturas e condições edafoclimáticas. Esse trabalho teve como objetivo principal avaliar o efeito do molhamento parcial do solo para plantas jovens de laranja Valência sob porta-enxerto de citrumelo Swingle e limão Cravo em dois tipos de solo. Os objetivos secundários foram: a) Avaliar o método da sonda de dissipação térmica na estimativa da transpiração em laranja Valência e b) Estabelecer as relações entre a transpiração das plantas, sem restrição de área de solo, molhado e a demanda atmosférica. O experimento foi conduzido em estufa nas dependências do Departamento de Engenharia de Biossistemas da ESALQ/USP. Foi testado o molhamento de 12,5% da área do solo. Mudas de laranja foram plantadas em caixas de 500 L internamente divididas em compartimentos. Determinou-se simultaneamente a transpiração de todas as plantas através de sondas de dissipação térmica, o conteúdo de água no solo, o crescimento das plantas (área foliar e diâmetro de caule) e o número total de frutos por planta. Inicialmente todas as plantas tiveram 100% do volume de solo ocupado pelas raízes irrigado, sendo determinada a contribuição relativa de cada compartimento da caixa na transpiração. Completada a secagem dos compartimentos não irrigados, foi calculado o percentual da transpiração relativa a 100% de área molhada do solo pela relação entre transpiração de cada planta e a transpiração média das plantas com 100% da área do solo molhado. De acordo com os resultados, conclui-se que ocorre redução da transpiração pela restrição da área de solo molhado, sendo esta redução influenciada não só pelo tipo de solo e porta-enxerto, como também pelo número de dias após início da irrigação parcial, demanda evaporativa da atmosfera e fase fenológica da planta. A adaptação do sistema radicular à redução da área molhada ocorreu em torno de 156 dias. Apesar da redução da taxa transpiratória, não houve diferença significativa entre os tratamentos em relação ao crescimento vegetativo e número de frutos por planta. A transpiração das plantas foi influenciada pelo tipo de porta-enxerto utilizado, do crescimento em área foliar e da fase fenológica, sendo que sua relação com a evapotranspiração de referência não é linear em toda faixa de demanda evaporativa da atmosfera. O método da sonda de dissipação térmica, com calibragem específica e correção dos gradientes térmicos naturais no caule, mostrou-se eficaz na avaliação da transpiração de plantas jovens de laranjeira. / The citrus industry is a great important sector to the Brazilian country to generate foreign currency income and capital formation. The determination of the fractional wetted area in the soil is a critical factor in the success of an irrigation system project. Due to the technical difficulties to find out dates in this kind of study, there are no reliable studies in the scientific literature to establish the optimal values of fractional wetted area for different crops, soil and weather. This study aims to evaluate the effect of partial wetting of the soil for Valencia orange under the rootstock Swingle and Rangpur in two soil types. As secondary objectives: a) To evaluate the method of heat dissipation probe in the transpiration estimative in the Valencia orange plant, b) to establish the relationship between the atmospheric demand and plant transpiration, without restriction wetted area. The experiment was conducted in a greenhouse in the Biosystems Engineering Department of ESALQ/USP, Piracicaba-SP, Brazil. It was tested the wetness of 12.5% of the area of soil. For this, orange seedlings were planted in boxes of 500 L internally divided into compartments. It was simultaneously determined transpiration of all plants using heat dissipation probes (sap flow), measured the soil water content, plant growth (leaf area, stem diameter) and the total number of fruits per plant. Initially, it was irrigated 100% of root system of all plants and it was determined the contribution of each compartment of the box in the plant transpiration by the difference in water storage in the soil and measured plant transpiration. When it was completed the drying of not irrigated compartment, it was calculated the percentage of transpiration on 100% of the wetted soil area by the relationship between transpiration of each plant and the average of plant transpiration with 100% of the wetted area. According to the results can be conclude that occur reduction in the transpiration flow due to the restricting of wet soil area and this reduction is not only influenced by soil type and rootstock, but also due to the number of days after onset of partial irrigation, atmospheric evaporative demand and plant phenological stage. The adaptation of the root system to the reduction of the wet soil volume occurred around 156 days. Despite of the reduction in transpiration rate, it was not observed significant difference between treatments in relation to vegetative growth and fruit number per plant. Plant transpiration was influenced by the type of rootstock used, leaf area growth and phenological stage. However the relationship between the plant transpiration and EToPM is not linear across the range of atmospheric evaporative demand. The method of heat dissipation probe, calibrated specifically for the study and with correction of the thermal natural gradient in the trunk was effective in the evaluation of the seedlings of orange transpiration.

A citricultura é um setor de grande importância para o país na geração de divisas, formação de renda e capital. Um dos fatores críticos no sucesso de um sistema de irrigação localizada é a definição em projeto da fração de área molhada no solo. Face às dificuldades técnicas encontradas nesse tipo de estudo, até o presente, inexistem na literatura científica trabalhos confiáveis que estabeleçam os valores ótimos de fração de área molhada no solo para as diferentes culturas e condições edafoclimáticas. Esse trabalho teve como objetivo principal avaliar o efeito do molhamento parcial do solo para plantas jovens de laranja Valência sob porta-enxerto de citrumelo Swingle e limão Cravo em dois tipos de solo. Os objetivos secundários foram: a) Avaliar o método da sonda de dissipação térmica na estimativa da transpiração em laranja Valência e b) Estabelecer as relações entre a transpiração das plantas, sem restrição de área de solo, molhado e a demanda atmosférica. O experimento foi conduzido em estufa nas dependências do Departamento de Engenharia de Biossistemas da ESALQ/USP. Foi testado o molhamento de 12,5% da área do solo. Mudas de laranja foram plantadas em caixas de 500 L internamente divididas em compartimentos. Determinou-se simultaneamente a transpiração de todas as plantas através de sondas de dissipação térmica, o conteúdo de água no solo, o crescimento das plantas (área foliar e diâmetro de caule) e o número total de frutos por planta. Inicialmente todas as plantas tiveram 100% do volume de solo ocupado pelas raízes irrigado, sendo determinada a contribuição relativa de cada compartimento da caixa na transpiração. Completada a secagem dos compartimentos não irrigados, foi calculado o percentual da transpiração relativa a 100% de área molhada do solo pela relação entre transpiração de cada planta e a transpiração média das plantas com 100% da área do solo molhado. De acordo com os resultados, conclui-se que ocorre redução da transpiração pela restrição da área de solo molhado, sendo esta redução influenciada não só pelo tipo de solo e porta-enxerto, como também pelo número de dias após início da irrigação parcial, demanda evaporativa da atmosfera e fase fenológica da planta. A adaptação do sistema radicular à redução da área molhada ocorreu em torno de 156 dias. Apesar da redução da taxa transpiratória, não houve diferença significativa entre os tratamentos em relação ao crescimento vegetativo e número de frutos por planta. A transpiração das plantas foi influenciada pelo tipo de porta-enxerto utilizado, do crescimento em área foliar e da fase fenológica, sendo que sua relação com a evapotranspiração de referência não é linear em toda faixa de demanda evaporativa da atmosfera. O método da sonda de dissipação térmica, com calibragem específica e correção dos gradientes térmicos naturais no caule, mostrou-se eficaz na avaliação da transpiração de plantas jovens de laranjeira. / The citrus industry is a great important sector to the Brazilian country to generate foreign currency income and capital formation. The determination of the fractional wetted area in the soil is a critical factor in the success of an irrigation system project. Due to the technical difficulties to find out dates in this kind of study, there are no reliable studies in the scientific literature to establish the optimal values of fractional wetted area for different crops, soil and weather. This study aims to evaluate the effect of partial wetting of the soil for Valencia orange under the rootstock Swingle and Rangpur in two soil types. As secondary objectives: a) To evaluate the method of heat dissipation probe in the transpiration estimative in the Valencia orange plant, b) to establish the relationship between the atmospheric demand and plant transpiration, without restriction wetted area. The experiment was conducted in a greenhouse in the Biosystems Engineering Department of ESALQ/USP, Piracicaba-SP, Brazil. It was tested the wetness of 12.5% of the area of soil. For this, orange seedlings were planted in boxes of 500 L internally divided into compartments. It was simultaneously determined transpiration of all plants using heat dissipation probes (sap flow), measured the soil water content, plant growth (leaf area, stem diameter) and the total number of fruits per plant. Initially, it was irrigated 100% of root system of all plants and it was determined the contribution of each compartment of the box in the plant transpiration by the difference in water storage in the soil and measured plant transpiration. When it was completed the drying of not irrigated compartment, it was calculated the percentage of transpiration on 100% of the wetted soil area by the relationship between transpiration of each plant and the average of plant transpiration with 100% of the wetted area. According to the results can be conclude that occur reduction in the transpiration flow due to the restricting of wet soil area and this reduction is not only influenced by soil type and rootstock, but also due to the number of days after onset of partial irrigation, atmospheric evaporative demand and plant phenological stage. The adaptation of the root system to the reduction of the wet soil volume occurred around 156 days. Despite of the reduction in transpiration rate, it was not observed significant difference between treatments in relation to vegetative growth and fruit number per plant. Plant transpiration was influenced by the type of rootstock used, leaf area growth and phenological stage. However the relationship between the plant transpiration and EToPM is not linear across the range of atmospheric evaporative demand. The method of heat dissipation probe, calibrated specifically for the study and with correction of the thermal natural gradient in the trunk was effective in the evaluation of the seedlings of orange transpiration.

High latitude and altitude ecosystems are currently undergoing rapid and unprecedented warming in response to anthropogenically induced climate change. Subarctic, alpine regions are particularly vulnerable to increases in air temperature and changing precipitation regimes, which have caused cascading hydrological and ecological impacts. In addition to changing flow regimes, thawing permafrost, and declining glaciers, widespread changes in vegetation composition, density and distribution have been observed across northern regions. Specifically, treeline is advancing with increasing latitude and altitude and shrubs are increasing in height, extent, and density. Despite widespread documentation of this northern greening, few field-based studies have evaluated the hydrological implications of these changes. Quantification of total evapotranspiration (ET) across a range of vegetation gradients is essential for predicting water yield, yet challenging in cold alpine catchments due to heterogeneous land cover. Direct field-level measurements of transpiration (T) and evaporative partitioning across subarctic, alpine ecosystems and species are rare, yet essential to assess sensitivities and hydrological response to changing climate drivers. This thesis presents six years of surface energy balance components and ET dynamics and two years of sap flux measurements and critical zone stable water isotope sampling at three sites along an elevational gradient in a subarctic, alpine catchment near Whitehorse, Yukon Territory, Canada. These sites span a gradient of thermal and vegetation regimes, providing a space-for-time comparison for future ecosystem shifts: 1) a low-elevation boreal white spruce forest (~12-20 m), 2) a mid-elevation subalpine taiga comprised of tall, dense willow (Salix) and birch (Betula) shrubs (~1-3 m) and 3) a high-elevation subalpine taiga with short, sparse shrub cover (< 0.75 m) and moss, lichen, and bare rock. We utilize both mass flux measurements and stable water isotopes to evaluate the timing, magnitude, sensitivities, and sources of plant water uptake across these vegetation covers. Total ET decreased and interannual variability increased with elevation, with mean May to September ET totals of 349 (±3) mm at the forest, 249 (±10) mm at the tall, dense shrub site, and 240 (± 26) mm at the short, sparse shrub site. The shrub sites exhibited similar ET losses over 6 years despite differences in shrub height and abundance, although daily rates were higher at the tall shrub site in the peak growing season. From May to September, ET:R ratios were the highest and most variable at the forest (2.19 ± 0.37) and similar at the tall, dense shrub (1.22 ± 0.09) and short, sparse shrub (1.14 ± 0.05) sites. In the mid-growing season, mean T rates were greater at the dense shrub site (2.0 ± 0.75 mm d-1) than the forest (1.47 ± 0.52 mm d-1). During this time, T:ET was lower at the forest (0.48) than at the tall, dense shrub site (0.80). During the growing season between the two years, 2020 was considerably wetter and cooler than 2019. At the tall shrub site, during the mid-growing season (July 1-Aug 15), T dropped considerably in 2020 (-26%), as T was suppressed during the short, wet growing season. In contrast, T at the forest was only moderately suppressed (-3%) between years in this same period. Evapotranspiration was more strongly controlled by air temperature during the early and late season at the forest, while ET at the shrub site was more sensitive to warmer temperatures in the mid-growing season. At the shrub sites, ET was energy limited with no observed soil moisture limitation on T. While 2H and 18O of volume weighted precipitation became more depleted with elevation, the opposite was true in xylem water, where 2H and 18O became more enriched with elevation. Plant water uptake was more reflective of snow water at the forest site than both shrub sites, particularly early in the year and during dry periods. Near-surface bulk soil water had more negative lc-excess at the forest throughout the season and with depth, highlighting increased contributions from soil evaporation. This study combined direct measurements of sap flux, ET, and critical zone isotopes to provide new details on multi-year plant-soil-water dynamics, critical zone water cycling, and species-specific plant water uptake patterns in seasonally frozen soils, which have not previously been reported in cold regions. Our results suggest that advances in treeline will increase overall ET and lower interannual variability; however, the large growing season water deficit and stable water isotope signature at the forest indicates strong reliance on soil moisture from late fall and snowmelt recharge and the potential for plant water stress. Differences between the shrub species were apparent in the sap flux and stable isotope measurements, highlighting the need to further evaluate species specific responses and feedbacks when predicting hydrological fluxes across subarctic ecosystems. Overall, our results suggest that predicted changes in vegetation type and structure in northern regions will have a considerable impact on water partitioning and will vary in a complex way in response to changing precipitation timing, phase and magnitude. / Thesis / Candidate in Philosophy

In the Mediterranean area water is a scarce natural resource and periods of drought are frequent. It is then important to increase water use efficiency of irrigated crops. In order to achieve this, one promising option is regulated deficit irrigation (RDI). RDI consists in reducing water application during stages of crop development when yield and fruit quality have low sensitivity to water stress. Full irrigation is provided during the rest of the season to maintain production and fruit quality at adequate levels (Behboudian and Mills, 1997). In citrus, flowering and fruit set are sensitive periods to water restrictions, because water stress during this period increases fruit drop (Ginestar and Castel 1996). The more appropriate phenological period for applying water restrictions seems to be the summer period providing that water applications returned at full dosage sufficiently before harvest in order to allow for compensation in fruit growth (Cohen and Goell 1988). Previous work by González-Altozano and Castel (1999) showed the feasibility of applying RDI in 'Clementina de Nules' and identified threshold values of plant water stress that allowed water savings of about 10-20% without any detrimental effect on yield or fruit size. It would be desirable now to study the extrapolation of these results to commercial orchards of citrus and assess the use of RDI in different citrus cultivars. Two RDI strategies (RDI-1, irrigated at 50% of crop evapotranspiration (ETc) during summer and; RDI-2, irrigated at 35% ETc during the same period to RDI-1) will be compared with a control treatment irrigated at full requirements. As the level of water stress reached by trees is the important factor when RDI strategies are applied, the study of accurate water stress indicators for citrus is also needed. Thus, during the period of water restrictions the use of sap flow and canopy temperature measurements, obtained by thermal imaging or by means of fixed infrared thermometer sensors, will be assessed and compared to classical methods like stem water potential and stomatal conductance. / Ballester Lurbe, C. (2013). Regulated deficit irrigation in citrus: agronomic response and water stress indicators [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/28582 / Premios Extraordinarios de tesis doctorales

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The thesis was intended to fill the information gap in the ecohydrology of the Pinus rotundata dominated peatbogs in the Třeboň Basin Biosphere Reserve, Czech Republic by studying various aspects of their water régime (i.e., transpiration of the dominant tree species, soil water chemistry, retention ability). The study is based on regular monitoring of the water table, water discharge, soil water chemistry and precipitation (during 1995-2000, study sites Červené blato and Žofinka peatbogs). Additionally, the transpiration of adult Pinus rotundata trees was measured in the field during 1999-2000 at the experimental plot in the Červené blato peatbog (330 ha, 465-475 m a.s.l.). Nowadays, the Pinus rotundata-dominated peatbogs represent almost natural (peaty) forests inside of otherwise human-made forest plantations. Long-term vegetation changes after natural disturbances such as windstorms, insect infestation and fire are only occasionally reported for the central European natural forests. Therefore the evaluation of vegetation changes after disturbances, typical of boreal forests, and their impact on peatbog hydrology has also been included in this thesis (study site Žofinka peatbog, 130 ha, 470-475 m a.s.l.). Transpiration of the central European endemic tree species, Pinus rotundata Link, was...

O uso crescente de irrigação na cafeicultura devido ao cultivo em áreas com maior deficiência hídrica exige conhecimento sobre o consumo de água da cultura. Para contribuir para esse conhecimento, a evapotranspiração global do cafezal (ETc) e sua partição nos fluxos componentes evapotranspiração das linhas de cafeeiros (ETlin), evapotranspiração das entrelinhas (ETel) e a transpiração dos cafeeiros (T) foram determinadas em um cafezal de Coffea arabica cv. Obatã IAC-1669-20, cultivado em Piracicaba, SP, em espaçamento de 3,50 m x 0,90 m, irrigado por gotejamento e idade entre 3 a 4 anos, com medidas de setembro/04 a maio/05 e em setembro e outubro de 2005. ETc foi determinada pelo método de balanço de energia-razão de Bowen, ETlin por lisímetros de células de carga, sendo estes usados em vários períodos com o solo coberto com plástico para determinação direta da transpiração e para calibrar o método da sonda de dissipação térmica, usado na determinação do fluxo de seiva (FS) dos cafeeiros. Em abril-maio/05, FS foi usado como uma estimativa de T diária. ETc e componentes foram relacionados com a evapotranspiração de referência estimada pelos métodos de Penman- Monteith (ETo 1) e do tanque classe A (ETo 2). O calor latente de vaporização (LE) representou a maior fração na partição da energia disponível (saldo de radiação menos fluxo de calor no solo), com variação de 73 a 80 % ao longo dos meses, não se podendo descartar a contribuição de calor advectivo para os valores encontrados nos meses secos. ETc cresceu a partir de setembro/04 a fevereiro/05 (2,75 a 4,58 mm d-1), refletindo principalmente o incremento de área foliar e diminuindo, posteriormente, até maio/05 (3,13 mm d-1) com a diminuição da demanda atmosférica. Em setembro-outubro/05 os valores foram maiores (2,93 e 4,29 mm d-1) do que os observados no mesmo período em 2004, sendo o aumento da área foliar uma das responsáveis pelo fato. A relação ETc/ETo ("Kc global da cultura") foi maior quando calculada com ETo 1 do que com ETo 2, sendo os valores crescentes até janeiro/05 (1,20 com ETo 1 e 1,21 com ETo 2) mas com o menor valor em setembro/04 (0,67 e 0,54) e com diminuição da tendência de acréscimo em fevereiro/05 (1,17 e 0,73), provavelmente pela regulação estomática dos cafeeiros devido à alta demanda atmosférica nesses meses. A contribuição de ETlin para a ETc variou pouco entre setembro/04 e fevereiro/05 (24 % a 31 %), aumentando em março e abril (35 % e 40 %), valores esses próximos da proporção entre a área de solo coberta pelos cafeeiros e a área total (linhas+entrelinhas). A relação ETlin/ETo variou entre 0,20 (uso de ETo 1) e 0,16 (com ETo 2) em setembro/04 a 0,36-0,47 (com ETo 1) e 0,25-0,49 nos outros meses. A T dos cafeeiros por unidade de área foliar diminuiu com o aumento da área foliar. A relação T/ETlin variou de 72 % em fevereiro a 46 % em abril, sendo o valor de T/ETo ("Kc basal") variável entre 0,13 (com ETo 1) e 0,10 (com ETo 2) em setembro a 0,30 (independente do método de estimativa de ETo) em abril e maio/04, provavelmente refletindo a menor atividade fisiológica. / The increasing use of irrigation in coffee plantations in Brazil, due to the deplacement of the crop to areas where water deficit occurs, requires knowledge about crop water consumption. Aiming to know more about coffee plantation water consumption, daily crop evapotranspiration (ETc) and its partition in row evapotranspiration (ETrow), interrows evapotanspiration (ETint) and coffee plants transpiration (T) were determined in a drip-irrigated coffee plantation (cv. Obatã IAC-1669-20), cultivated at 3.5 m between rows and 0.9m between plants, in Piracicaba, São Paulo State, Brazil. The ET and wheater variables measurements were carried out from September 2004 to May 2005 and from September to October 2005. ETc was determined by he Bowen ratio-energy balance method, ETrow by load cell lysimeters and T with lysimeters with soil surface covered with plastic or by sap flow determined with the thermal dissipation probe method (TDP). Lysimeters were also used to calibrate the TDP method. So, sap flow was adopted as representative of coffee plants transpiration for 24-h period. ET and its components were related to the reference evapotranspiration, determined by Penman-Monteith (ETo 1) and Class-A pan (ETo 2) methods. Latent heat of vaporization (LE) represented the major fraction (73 a 80 %) of the available energy (net radiation less soil heat flux) along the months, but a contribution of advective heat flux in dry months must be considered for the observed values. ETc increased from September 2004 to February 2005 (from 2.75 to 4.58 mm d-1), which is reflecting the increase of coffee plants leaf area. From March to May 2005, ETc decreased according to the decrease of the atmospheric demand. In September and October 2005, ETc were greater, respectively, 2.93 and 4.29 mm d-1, than those observed in the same months of 2004 and, again the increase of leaf area was the responsable for these differences. ETc/ETo, defined as a "global Kc", was greater when determined with ETo 1 than when determined with ETo 2, increasing with the leaf area.from September 2004 (0.67 with ETo 1 and 0.54 with ETo 2) to January 2005 (1,20 and 1,21). In February Kc decreased to 1.17 (with ETo 1) and 0.73 (with ETo 2), probably as a consequence of the coffee plants stomatal control due to the high atmospheric demand. The contribution of ETrow to ETc varied between 25 % and 31 % for the period September 2004- February 2005, increasing in March and April 2005 (35 % and 40 %). These values were close to those observed for the ratio between the area of soil covered by coffee plants and the total area (rows+interrows). ETlin/ETo changed from 0.20 or 0.16 (using ETo 1 and ETo 2, respectively) in September 2004 to 0.36-0.47 (with ETo 1) or 0.25- 0.49 (with ETo 2) in the other months. Coffee plant transpiration per leaf area unit decresead with the increase of leaf area. T/ETrow changed from 0.72 (February) to 0.46 (April). T/ETo ("basal Kc") ranged from 0.13 (with ETo 1) or 0.10 (with ETo 2) in September 2004 to 0.30 (for both ETo 1 or ETo 2) in February, but decreased in April and May 2005, probably reflecting the decrease in the physiological activity of coffee plants.

O uso crescente de irrigação na cafeicultura devido ao cultivo em áreas com maior deficiência hídrica exige conhecimento sobre o consumo de água da cultura. Para contribuir para esse conhecimento, a evapotranspiração global do cafezal (ETc) e sua partição nos fluxos componentes evapotranspiração das linhas de cafeeiros (ETlin), evapotranspiração das entrelinhas (ETel) e a transpiração dos cafeeiros (T) foram determinadas em um cafezal de Coffea arabica cv. Obatã IAC-1669-20, cultivado em Piracicaba, SP, em espaçamento de 3,50 m x 0,90 m, irrigado por gotejamento e idade entre 3 a 4 anos, com medidas de setembro/04 a maio/05 e em setembro e outubro de 2005. ETc foi determinada pelo método de balanço de energia-razão de Bowen, ETlin por lisímetros de células de carga, sendo estes usados em vários períodos com o solo coberto com plástico para determinação direta da transpiração e para calibrar o método da sonda de dissipação térmica, usado na determinação do fluxo de seiva (FS) dos cafeeiros. Em abril-maio/05, FS foi usado como uma estimativa de T diária. ETc e componentes foram relacionados com a evapotranspiração de referência estimada pelos métodos de Penman- Monteith (ETo 1) e do tanque classe A (ETo 2). O calor latente de vaporização (LE) representou a maior fração na partição da energia disponível (saldo de radiação menos fluxo de calor no solo), com variação de 73 a 80 % ao longo dos meses, não se podendo descartar a contribuição de calor advectivo para os valores encontrados nos meses secos. ETc cresceu a partir de setembro/04 a fevereiro/05 (2,75 a 4,58 mm d-1), refletindo principalmente o incremento de área foliar e diminuindo, posteriormente, até maio/05 (3,13 mm d-1) com a diminuição da demanda atmosférica. Em setembro-outubro/05 os valores foram maiores (2,93 e 4,29 mm d-1) do que os observados no mesmo período em 2004, sendo o aumento da área foliar uma das responsáveis pelo fato. A relação ETc/ETo (“Kc global da cultura”) foi maior quando calculada com ETo 1 do que com ETo 2, sendo os valores crescentes até janeiro/05 (1,20 com ETo 1 e 1,21 com ETo 2) mas com o menor valor em setembro/04 (0,67 e 0,54) e com diminuição da tendência de acréscimo em fevereiro/05 (1,17 e 0,73), provavelmente pela regulação estomática dos cafeeiros devido à alta demanda atmosférica nesses meses. A contribuição de ETlin para a ETc variou pouco entre setembro/04 e fevereiro/05 (24 % a 31 %), aumentando em março e abril (35 % e 40 %), valores esses próximos da proporção entre a área de solo coberta pelos cafeeiros e a área total (linhas+entrelinhas). A relação ETlin/ETo variou entre 0,20 (uso de ETo 1) e 0,16 (com ETo 2) em setembro/04 a 0,36-0,47 (com ETo 1) e 0,25-0,49 nos outros meses. A T dos cafeeiros por unidade de área foliar diminuiu com o aumento da área foliar. A relação T/ETlin variou de 72 % em fevereiro a 46 % em abril, sendo o valor de T/ETo (“Kc basal”) variável entre 0,13 (com ETo 1) e 0,10 (com ETo 2) em setembro a 0,30 (independente do método de estimativa de ETo) em abril e maio/04, provavelmente refletindo a menor atividade fisiológica. / The increasing use of irrigation in coffee plantations in Brazil, due to the deplacement of the crop to areas where water deficit occurs, requires knowledge about crop water consumption. Aiming to know more about coffee plantation water consumption, daily crop evapotranspiration (ETc) and its partition in row evapotranspiration (ETrow), interrows evapotanspiration (ETint) and coffee plants transpiration (T) were determined in a drip-irrigated coffee plantation (cv. Obatã IAC-1669-20), cultivated at 3.5 m between rows and 0.9m between plants, in Piracicaba, São Paulo State, Brazil. The ET and wheater variables measurements were carried out from September 2004 to May 2005 and from September to October 2005. ETc was determined by he Bowen ratio-energy balance method, ETrow by load cell lysimeters and T with lysimeters with soil surface covered with plastic or by sap flow determined with the thermal dissipation probe method (TDP). Lysimeters were also used to calibrate the TDP method. So, sap flow was adopted as representative of coffee plants transpiration for 24-h period. ET and its components were related to the reference evapotranspiration, determined by Penman-Monteith (ETo 1) and Class-A pan (ETo 2) methods. Latent heat of vaporization (LE) represented the major fraction (73 a 80 %) of the available energy (net radiation less soil heat flux) along the months, but a contribution of advective heat flux in dry months must be considered for the observed values. ETc increased from September 2004 to February 2005 (from 2.75 to 4.58 mm d-1), which is reflecting the increase of coffee plants leaf area. From March to May 2005, ETc decreased according to the decrease of the atmospheric demand. In September and October 2005, ETc were greater, respectively, 2.93 and 4.29 mm d-1, than those observed in the same months of 2004 and, again the increase of leaf area was the responsable for these differences. ETc/ETo, defined as a “global Kc”, was greater when determined with ETo 1 than when determined with ETo 2, increasing with the leaf area.from September 2004 (0.67 with ETo 1 and 0.54 with ETo 2) to January 2005 (1,20 and 1,21). In February Kc decreased to 1.17 (with ETo 1) and 0.73 (with ETo 2), probably as a consequence of the coffee plants stomatal control due to the high atmospheric demand. The contribution of ETrow to ETc varied between 25 % and 31 % for the period September 2004- February 2005, increasing in March and April 2005 (35 % and 40 %). These values were close to those observed for the ratio between the area of soil covered by coffee plants and the total area (rows+interrows). ETlin/ETo changed from 0.20 or 0.16 (using ETo 1 and ETo 2, respectively) in September 2004 to 0.36-0.47 (with ETo 1) or 0.25- 0.49 (with ETo 2) in the other months. Coffee plant transpiration per leaf area unit decresead with the increase of leaf area. T/ETrow changed from 0.72 (February) to 0.46 (April). T/ETo (“basal Kc”) ranged from 0.13 (with ETo 1) or 0.10 (with ETo 2) in September 2004 to 0.30 (for both ETo 1 or ETo 2) in February, but decreased in April and May 2005, probably reflecting the decrease in the physiological activity of coffee plants.