A better understanding of the hydrogeology of mine waste rock and cover systems is essential for the quantification, prediction and reduction of metals loading to the receiving environment. A series of experiments were conducted on an instrumented intermediate-scale waste rock pile at the Cluff Lake Mine in Saskatchewan to investigate the changes in flow and solute transport within coarse waste rock under three different surface conditions. Following these studies, the waste rock pile was deconstructed, structures were mapped, and samples were collected for physical characterization and pore water extraction. The internal structure of the waste rock pile was more important than the texture and topography under the free-dumped and ripped/leveled surface, while the surface condition was found to be the dominant control on spatial and temporal variability of outflow from the waste rock with the covered surface. Data from a deuterium tracer test, lysimeter outflow, and from TDR probes were used to derive estimates of the maximum and an average pore water velocity through the uncovered and the covered waste rock. An average pore water velocity through the matrix materials of the uncovered waste rock was approximately 1.5 m/yr and maximum preferential flow velocities were as high as 5 m/day. The post-cover pressure wave velocity of 0.1 to 1 m/day is inferred from outflow and TDR data, and average pore water velocities (0.39 m/y and 0.73 m/y) are calculated by the water flux and tracer methods, respectively. The distribution of the tracers in pore water and the internal structure were mapped during a detailed deconstruction of the waste rock pile and attempts were made to link the data to the spatial and temporal patterns of lysimeter outflow. The pore water chloride concentrations and the deuterium values did not provide conclusive data necessary to link the spatial and temporal patterns observed in the lysimeter hydrographs to internal structure; however, it provided insight into the internal flow mechanisms and water residence times.

Submitted by LUÍS GUILHERME POLIZEL LIBARDI null (lgplibardi@gmail.com) on 2018-01-27T15:29:33Z No. of bitstreams: 1 Dissertação - Versão Digital.pdf: 2640206 bytes, checksum: bad6e8febf253e2526f7f86e7c6e49e6 (MD5) / Approved for entry into archive by Karina Gimenes Fernandes null (karinagi@fcav.unesp.br) on 2018-01-29T12:54:39Z (GMT) No. of bitstreams: 1 libardi_lgp_me_jabo.pdf: 2595561 bytes, checksum: 77d88f2a795f0ab5ee9a02d2f29a9eb5 (MD5) / Made available in DSpace on 2018-01-29T12:54:39Z (GMT). No. of bitstreams: 1 libardi_lgp_me_jabo.pdf: 2595561 bytes, checksum: 77d88f2a795f0ab5ee9a02d2f29a9eb5 (MD5) Previous issue date: 2017-12-08 / A produção de mudas pré-brotadas (MPB) de cana-de-açúcar é um método inovador que visa aumentar a taxa de multiplicação da cultura. O sistema é conduzido em cultivo protegido, no qual o manejo correto de irrigação é fator essencial para manter a qualidade da produção. O objetivo do estudo foi expor detalhes da construção e calibração de três lisímetros de pesagem de baixo custo e utilizá-los para determinar evapotranspiração de cultura (ETc) e coeficiente de cultura (Kc) de MPB de três cultivares de cana-de-açúcar (CTC9005HP, RB966928 e SP87365), aliados à análise de crescimento, para manejo de irrigação em cultivo protegido. Três lisímetros de pesagem foram construídos especificamente para MPB em casa de vegetação da Usina São Martinho (São Martinho S/A), cada qual com área de 0,6909 m2 (1179 mm x 586 mm), profundidade de 400 mm e apoiados sobre 3 células de carga. A calibração dos lisímetros demonstrou precisão e acurácia na detecção de variações de massa equivalente em torno de 0,1 mm pelos equipamentos e magnitude de histerese que não comprometeu as avaliações de evapotranspiração. O custo de equipamentos foi baixo, exceto o sistema de aquisição de dados. A determinação de ETc e cálculo de ETo pelo método FAO-56 possibilitaram inferir valores de Kc ao longo do ciclo de produção. O consumo hídrico, determinado pela ETc, variou de 3,0 a 6,9 mm d-1 na CTC9005HP, 3,1 a 6,8 mm d-1 na RB966928 e 2,9 a 6,6 mm d-1 na SP87365. Kc teve elevação de 1,00 a 1,46 na CTC9005HP, 1,02 a 1,53 na RB966928 e 1,02 a 1,49 na SP87365. A poda das folhas aos 37 dias após a transferência reduziu ETc e, consequentemente, Kc dos tratamentos. Altura de colmos foi superior em SP87365 e CTC9005HP e diâmetro de colmos em RB966928. SP87365 foi superior à CTC9005HP nas avaliações foliares. Massas frescas e secas de colmos e total não diferiram entre cultivares. Épocas de avaliação apresentaram diferenças nas avaliações, confirmando o crescimento das plantas. Portanto, ETc e Kc de MPB foram determinadas por lisímetros de precisão de baixo custo, aliados à análise de crescimento, para manejo de irrigação de MPB em cultivo protegido. / The pre-sprouted sugarcane plantlets production system (PSS) is an innovative method to enhance crop multiplication rates. This system is greenhouse-grown, where correct irrigation management is essential to maintain the production quality. The purpose of this study was to detail construction and calibration of three low-cost weighing lysimeters and to use them to determine crop evapotranspiration (ETc) and crop coefficient (Kc), allied to growth analysis, of three sugarcane cultivars (CTC9005HP, RB966928 and SP87365), for irrigation management of greenhouse grown PSS. Three specific PSS weighing lysimeters were built in a greenhouse at São Martinho Mill (São Martinho S/A) and covered 0.6909 m2 (1179 mm x 586 mm) with 400 mm depth supported by 3 load cells. The lysimeters calibration showed precision and accuracy detection of equivalent-mass variations around 0.1 mm and hysteresis that did not compromise evapotranspiration measurements. Low cost materials were used in this study, excluding acquisition data system. Determined ETc and calculated FAO-56 ETo resulted in production cycle Kc values. Water requirement, determined by ETc, ranged from 3.0 to 6.9 mm d-1 in CTC9005HP, 3.1 to 6.8 mm d-1 in RB966928 and 2.9 to 6.6 mm d-1 in SP87365. Kc increased from 1.00 to 1.46 in CTC9005HP, 1.02 to 1.53 in RB966928 and 1.02 to 1.49 in SP87365. Treatments leaves pruning at 37 days after transference to greenhouse decreased ETc and, consequently, Kc. Stalk height was higher in SP87365 and CTC9005HP and stalk diameter in RB966928. SP87365 was superior to CTC9005HP in leaf evaluations. Total and stalk fresh and dry masses did not differ between cultivars. Evaluation periods presented difference in evaluations, confirming plants growth. Therefore, ETc and Kc were successfully determined by built precision low-cost lysimeters, allied to growth analysis, for PSS irrigation management in greenhouse grown.

O conhecimento da demanda hídrica de uma cultura é fundamental para o planejamento da implantação de novas áreas, bem como para a análise da viabilidade econômica de uma cultura em determinada região. A utilização de culturas para fontes de matéria prima alternativa vem sendo altamente estudada nos últimos anos. Dentre muitas, vem se destacando no cenário nacional e mundial a cultura do pinhão-manso (Jatropha curcas L.) para a produção de biodiesel. O consumo de água por parte do pinhão-manso é pouco conhecida, necessitando ser estudada a fim de aprofundar os conhecimentos sobre a cultura e fornecer parâmetros confiáveis para a prática da irrigação. Os objetivos desse trabalho foram determinar a evapotranspiração (ET), a evaporação (E), a transpiração (T), o coeficiente de cultivo (Kc), coeficiente de evaporação (Ke) e coeficiente de cultivo basal (Kcb) do pinhão-manso na fase de formação irrigados por pivô central, gotejamento e sem irrigação na cidade de Piracicaba, SP. O experimento foi realizado na Fazenda Areão da Escola Superior de Agricultura \"Luiz de Queiroz\" da USP durante o período de março de 2012 a abril de 2013. O experimento foi dividido em três tratamentos, sendo: irrigado por pivô central, gotejamento e sem irrigação. A determinação de ET foi realizada por meio lisímetros de pesagem em cada tratamento, contabilizando a variação de massa em função das entradas saídas de água no sistema. A determinação do Kc foi realizada pela razão entre ET e ETo (estimado a partir de dados coletados na estação meteorológicos automática da Fazenda Areão). Por meio de microlisímetros de pesagem, foi determinado E. De posso dos dados de E, foram determinados os valores de T pela diferença de E (determinado no microlisímetro) e ET (determinado no lisímetro). Os valores de Ke e Kcb foram determinados pela razão de E e T por ETo, respectivamente. Os valores de ET variaram, principalmente, em função do método de irrigação. Foi observado uma superioridade dos valores de ET para o tratamento irrigado por pivô central, seguido do tratamento irrigado por gotejamento e sem irrigação. As médias dos tratamentos durante o primeiro ano foram 3,17, 2,82 e 2,82 mm dia-1 para os tratamentos irrigado por pivô central, irrigado por gotejamento e sem irrigação, respectivamente. Essa mesma proporção de ET entre os tratamentos irrigados foi observado nos valores de Kc. A média do período de Kc foi 0,69 e 0,63 para os tratamentos irrigados por pivô central e gotejamento. Essas maiores taxas de ET e Kc do tratamento irrigado por pivô central em relação ao tratamento irrigado por gotejamento foi devido ao método de irrigação por gotejamento ser mais eficiente na utilização de água pelas plantas em relação ao método por pivô central. Nesse método, a água é aplicada de maneira localizada as plantas, diferentemente do método por pivô central, em que a água é aplicada em toda a superfície do solo. Isso faz com que as taxas de E no método por gotejamento seja menor em relação ao pivô central, diminuindo as taxas de ET. De maneira geral, as taxas de E e Ke foram maiores em relação aos valores de T e Kcb durante o período analisado. Isso foi devido as plantas estarem com porte baixo e o solo estar quase por completo exposto as variações atmosféricas, fazendo com que as taxas de E e Ke sejam superiores as de T e Kcb. A média de E e Ke foram 1,85 mm dia-1 e 1,03, respectivamente, e as médias de T e Kcb foram 0,4 mm dia-1 e 0,2, respectivamente. / The knowledge of the water demand of a culture is essential for planning of new areas, as well as for the economic viability analysis of a culture in a specific region. The use of crops for alternative feedstock sources has been extensively studied in the last years. Among many, jatropha (Jatropha curcas L.) has been highlighted for biodiesel production in the national and global scenarios. Water consumption by the jatropha is little known, which requires to be studied in order to increase the knowledge and provide reliable parameters for the irrigation practice. The objectives of this study were to determine the evapotranspiration (ET), evaporation (E), transpiration (T), crop coefficient (Kc), evaporation coefficient (Ke) and basal crop coefficient (Kcb) of jatropha in the formation phase irrigated by center pivot, drip and without irrigation in Piracicaba, SP. The experiment was conducted at Areão Farm of Escola Superior de Agricultura \"Luiz de Queiroz\" of USP during March 2012 to April 2013. The experiment included three treatments: center pivot irrigated, drip irrigated and dryland. The determination of ET was made by weighing lysimeters for each treatment, accounting the inputs and outputs of water in the lysimeter system. The determination of Kc was made by the ratio between ET and ETo (estimated from data collected at the automatic meteorological station of Areão Farm). The determination of E was made by microlysimeters and T was determined between the difference of ET and E. Ke and Kcb values were determined by the ratio of E and T by ETo, respectively. ET values varied, mainly, according to the irrigation method. It was observed superiority of ET values for the treatment irrigated by center pivot, followed by the treatment irrigated by drip and without irrigation. The average during the first year was 3.17, 2.82 and 2.82 mm day-1 for the treatment irrigated by center pivot, irrigated by drip irrigated and without irrigation, respectively. The same proportion of ET from irrigated treatments was observed in the values of Kc. In the period, the average of Kc was 0.69 and 0.63 for the treatments irrigated by center pivot and irrigated by drip. These higher rates of ET and Kc of the treatment irrigated by center pivot compared to the treatment irrigated by drip was due to the method of drip irrigation is more efficient in water use by plants in relation to the method irrigated by central pivot. In this method, the water application is made in a localized way, differently in relation to the center pivot method in which water is applied all over the soil surface. This makes E rates given by drip irrigation method lower than the center pivot irrigation method, decreasing its ET averages. In general, rates of E and Ke were higher compared T and Kcb values during the period analyzed. This was explained due the short plants stature and the soil was almost completely exposed to atmospheric variations, causing rates of E and Ke exceed from T and Kcb rates. The average of Ke and E were 1.85 mm day-1 and 1.03, respectively, and the average of T and Kcb were 0.4 mm day-1 and 0.2, respectively.

A better understanding of the hydrogeology of mine waste rock and cover systems is essential for the quantification, prediction and reduction of metals loading to the receiving environment. A series of experiments were conducted on an instrumented intermediate-scale waste rock pile at the Cluff Lake Mine in Saskatchewan to investigate the changes in flow and solute transport within coarse waste rock under three different surface conditions. Following these studies, the waste rock pile was deconstructed, structures were mapped, and samples were collected for physical characterization and pore water extraction. The internal structure of the waste rock pile was more important than the texture and topography under the free-dumped and ripped/leveled surface, while the surface condition was found to be the dominant control on spatial and temporal variability of outflow from the waste rock with the covered surface. Data from a deuterium tracer test, lysimeter outflow, and from TDR probes were used to derive estimates of the maximum and an average pore water velocity through the uncovered and the covered waste rock. An average pore water velocity through the matrix materials of the uncovered waste rock was approximately 1.5 m/yr and maximum preferential flow velocities were as high as 5 m/day. The post-cover pressure wave velocity of 0.1 to 1 m/day is inferred from outflow and TDR data, and average pore water velocities (0.39 m/y and 0.73 m/y) are calculated by the water flux and tracer methods, respectively. The distribution of the tracers in pore water and the internal structure were mapped during a detailed deconstruction of the waste rock pile and attempts were made to link the data to the spatial and temporal patterns of lysimeter outflow. The pore water chloride concentrations and the deuterium values did not provide conclusive data necessary to link the spatial and temporal patterns observed in the lysimeter hydrographs to internal structure; however, it provided insight into the internal flow mechanisms and water residence times. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

To quantify the energy balance above a lysimeter without disturbance of the measured air volume itself, the applicability of an acoustic-meteorological measurement method is numerically investigated. Several sound paths between transmitters and receivers around the lysimeter border an air volume (‚acoustic chamber’) to determine the interaction between the ground surface and the environment with remote sensing. This study is focused on the sensitivity of the acoustically derived air temperature and wind vector values. To describe the uncertainty of these quantities outgoing from the uncertainty of the acoustic travel time, several effects on the sound propagation, e.g. air absorption, ground reflection, and atmospheric refraction are studied. Based on the wind and temperature data at several height levels, momentum and heat fluxes can be derived which are important for the energy exchange above the lysimeter surface. First results of the achievable accuracy for the fluxes are summarized in the study using a numerical model of the atmospheric boundary layer.

Agronomic and water quality impacts of urea particle size were evaluated through field and laboratory experiments and mathematical modeling. In a two-year field study, corn silage yield, corn nitrogen (N) removal, and nitrate-N (NO₃⁻-N) leaching from urea pellets (1.5 g each) and granules (0.01-0.02 g each) applied at 184 kg-N/ha were compared. A control treatment (no N) and two other N application rates (110 and 258 kg-N/ha) were also included. Urea particle size impact on dissolution rate, dissolved urea movement, mineralization, and N0³-N leaching were evaluated in the laboratory. A two-dimensional (2-D) mathematical model was developed to simulate the fate of subsurface-banded urea and its transformation products, ammonium (NH₄⁺)and NO₃⁻. With 184 kg-N/ha, corn silage yield was 15% higher (p = 0.02) and corn N removal was 19% higher (p = 0.07) with pellets than granules in the second year of the field study. In the absence of yield response at 110 kg-N/ha, reason for higher yield at 184 kg-N/ha with pellets was unclear. Greater N removal reduced NO₃⁻-N leaching potential from pellets compared to granules during the over-winter period. No urea form response to yield or corn N removal was observed in the first year. In 23 of 27 sampling events, granules had higher NO₃⁻-N concentration in the root zone than pellets, with average nitrate-N concentrations of 2.6 and 2.2 mg-N/L, respectively. However, statistically, NO₃⁻-N leaching from the root zone was unaffected by urea form, probably due to high variability within treatments masking the treatment effects. In October 1997, pellets retained 16% more (p = 0.04) inorganic-N in the top half of the root zone than granules, due to slower nitrification in pellets as was determined in the mineralization study. Slower NO₃⁻-N leaching allowed for greater N extraction by plants. Pellets had lower dissolution, urea hydrolysis, and nitrification rates than granules; however, nitrification inhibition was the dominant mechanism controlling N fate. The model took into account high substrate concentration effects on N transformations, important for simulating the fate of band-applied N. The model exhibited good mass conservative properties, robustness, and expected moisture and N distribution profiles. Differences in measured field data and model outputs were likely due to uncertainties and errors in measured data and input parameters. Model calibration results indicated that moisture-related parameters greatly affected N fate simulation. Sensitivity analyses indicated the importance of nitrification-related parameters in N simulation, particularly, their possible multiplicative effects. Need for extensive model testing and validation was recognized. The validated 2-D N model could be incorporated into a management model for better management of subsurface-banded granular N. However, the 2-D model is not appropriate for simulating the three dimensional N movement from pellets. / Ph. D.

No description available.

Despite being the driest inhabited continent, Australia has one of the highest per capita water consumptions in the world. In addition, instead of having fit-for-purpose water supplies (using different qualities of water for different applications), highly treated drinking water is used for nearly all of Australia's urban water supply needs, including landscape irrigation. The water requirement of urban landscapes, particularly urban parklands, is of growing concern. The estimation of evapotranspiration (ET) and subsequently plant water requirements in urban vegetation needs to consider the heterogeneity of plants, soils, water, and climate characteristics. This research contributes to a broader effort to establish sustainable irrigation practices within the Adelaide Parklands in Adelaide, South Australia. In this paper, two practical ET estimation approaches are compared to a detailed Soil Water Balance (SWB) analysis over a one year period. One approach is the Water Use Classification of Landscape Plants (WUCOLS) method, which is based on expert opinion on the water needs of different classes of landscape plants. The other is a remote sensing approach based on the Enhanced Vegetation Index (EVI) from Moderate Resolution Imaging Spectroradiometer (MODIS) sensors on the Terra satellite. Both methods require knowledge of reference ET calculated from meteorological data. The SWB determined that plants consumed 1084 mmyr(-1) of water in ET with an additional 16% lost to drainage past the root zone, an amount sufficient to keep salts from accumulating in the root zone. ET by MODIS EVI was 1088 mmyr(-1), very close to the SWB estimate, while WUCOLS estimated the total water requirement at only 802 mmyr(-1), 26% lower than the SWB estimate and 37% lower than the amount actually added including the drainage fraction. Individual monthly ET by MODIS was not accurate, but these errors were cancelled out to give good agreement on an annual time step. We conclude that the MODIS EVI method can provide accurate estimates of urban water requirements in mixed landscapes large enough to be sampled by MODIS imagery with 250-m resolution such as parklands and golf courses.

A quantificação da evapotranspiração é uma tarefa essencial para a determinação do balanço hídrico em uma bacia hidrográfica e para o estabelecimento do déficit hídrico de uma cultura. Nesse sentido, o presente trabalho aborda a análise da evapotranspiração de referência (ETo) para a região de Jaboticabal-SP. O comportamento do fenômeno na região foi estudado a partir da interpretação de dados de uma bateria de 12 lisímetros de drenagem (EToLis) e estimativas teóricas por 10 equações diferentes disponíveis na literatura. A análise estatística de correlação indica que as estimativas da ETo por equações teóricas comparadas à EToLis medida em lisímetro de drenagem não apresentaram bons índices de comparação e erro. Admitindo que a operação dos lisímetros não permitiu a determinação da ETo com boa confiabilidade, propôs-se um ajuste local das demais metodologias de estimativa da ETo, através de auto-regressão (AR) dos ruídos destas equações em comparação com uma média anual estimada pela equação de Penman-Monteith (EToPM), tomada como padrão, em períodos quinzenal e mensal. O ajuste através de regressão linear simples também foi analisado. Os resultados obtidos indicam que a radiação efetiva é a variável climática de maior importância para o estabelecimento da ETo na região. A estimativa pela equação de Penman-Monteith apresentou excelente concordância com as equações de Makkink (1957) e do balanço de energia. Os ajustes locais propostos apresentaram excelentes resultados para a maioria das equações testadas, dando-se destaque às equações da radiação solar FAO-24, de Makkink (1957), de Jensen-Haise (1963), de Camargo (1971), do balanço de radiação, de Turc (1961) e de Thornthwaite (1948). O ajuste por regressão linear simples é de mais fácil execução e apresentou excelentes resultados. / The quantification of the evapotranspiration is an essential task for the determination of the water balance in a watershed and for the establishment of the culture´s water deficit. Therefore, the present work describes the analysis of the reference evapotranspiration (ETo) for the region of Jaboticabal-SP. The phenomenon behavior in the region was studied based on the interpretation of 12 drainage lysimeters data (EToLis) and on theoretical estimates for 10 different equations available in the Literature. An statistical analysis indicated that the theoretical ETo estimates compared with the EToLis did not present good indices of comparison and error. Admitting that the lysimeters operation did not allow a reliable ETo determination, a local adjustment of the theoretical methodologies for ETo estimate was considered. An auto-regression (AR) of the noises of these equations in comparison with the annual average estimate for the Penman-Monteith equation (EToPM), taken as standard, has been performed in fortnightly and monthly periods. The adjustment through simple linear regression has also been analyzed. The obtained results indicate that the effective radiation is the most important climatic variable for the establishment of the ETo in the region. The Penman-Monteith estimate presented excellent correlation to the estimates by Makkink (1957) equation and the energy balance. The local adjustments presented excellent results for the majority of the tested equations, specially for the solar radiation FAO-24, Makkink (1957), Jensen-Haise (1963), Camargo (1971), radiation balance, Turc (1961) and Thornthwaite (1948) equations. The adjustment by simple linear regression is of easier execution and also presented excellent results.

A irrigação de pastagens no Brasil apresentou um crescimento acentuado nos últimos anos, porém devido a ausência de pesquisas sobre a aplicação de água em pastagens, o manejo da irrigação não vem sendo realizado de maneira racional. Os objetivos deste trabalho foram avaliar as relações entre a irradiância solar global e a radiação líquida sobre superfícies vegetadas com capim tânzania (Panicum maximum Jacq.) e com grama batatais (Paspalum notatum flugge); determinar a evapotranspiração do capim tânzania, por meio das medidas de lisímetro de pesagem; aplicar o método do balanço de energia para a estimativa da evapotranspiração do capim tânzania, por meio de um sistema automático de razão de Bowen; e comparar os valores de evapotranspiração do capim tanzânia, medidos em lisímetro de pesagem com os estimados pelo balanço de energia por meio de um sistema automático de razão de Bowen. O experimento foi conduzido em Piracicaba, estado de São Paulo. Por meio de um lisímetro de pesagem e um sistema automático de razão de Bowen foram obtidos valores de evapotranspiração do capim tanzânia (ETc). Também foram obtidos dados de irradiância solar global (Qg) e radiação líquida (Rn) sobre grama batatais e capim tanzânia. Os dados foram coletados diariamente e analisados, estatisticamente, mediante análise de regressão. Os modelos de regressão linear de estimativa da radiação líquida encontrados foram Rn = 0,5418.Qg (r 2 = 0,9297) para uma superfície gramada e Rn = 0,5613.Qg (r 2 = 0,8719) para uma superfície vegetada pelo capim tanzânia. A evapotranspiração média do capim tanzânia foi de 4,13 mm.d -1 , segundo o balanço de energia e 4,34 mm.d -1 , obtido pelo lisímetro de pesagem. Com base nos resultados, concluiu-se que o valores de evapotranspiração diários e horários do capim tanzânia medidos pelo sistema automático de razão de Bowen, foram afetados pelo efeito advectivo e pela precipitação, mas apesar disso houve uma razoável correlação com as medidas feitas em lisímetro de pesagem; e o estabelecimento das relações apresentadas neste trabalho mostra que os saldos de radiação em superfície gramada, assim como no capim tanzânia, podem ser estimados satisfatoriamente a partir da irradiância solar global, tendo a necessidade de se considerar suas variações sazonais. / Pasture irrigation presented a large growth in Brazil in recent years. However, the lack of research on pasture water use has led to inefficient irrigation management practices. The objectives of this work were: to evaluate the relationships between global solar irradiance and net radiation on surfaces covered with Guinea grass (Panicum maximum Jacq.) and Bahia grass (Paspalum notatum flugge); to determine the evapotranspiration of Guinea grass through weighing lysimeter measurements; to apply the energy balance method to estimate the evapotranspiration of Guinea grass by means of an automated Bowen ratio system; and finally to compare the evapotranspiration of Guinea grass measured by a weighing lysimeter versus the evapotranspiration estimated by the automated Bowen ratio energy balance system.. Evapotranspiration (ETc) was obtained for Guinea grass by means of a weighing lysimeter and an automated Bowen ratio system. Global solar irradiance (Qg) and the net radiation (Rn) over Bahia grass and Guinea grass were also obtained. The data were collected daily and statistically analyzed through regression analysis. The linear regression models for Rn estimates were Rn = 0,5418.Qg (r 2 = 0,9297) for a Bahia grass surface and Rn = 0,5613.Qg (r 2 = 0,8719) for a surface covered with Guinea grass. Guinea grass average evapotranspiration was 4.13 mm.day -1 by the energy balance method and 4.34 mm.day -1 as measured by the weighing lysimeter. The results led to the conclusion that the daily and hourly evapotranspiration values of Guinea grass obtained by the Bowen ratio automated system, were affected by the advection and by precipitation. Despite that, it was possible to obtain a correlation between the Bowen ratio evapotranspiration and measurements with the weighing lysimeter. The results show that the net radiation over Bahia grass and Guinea grass can satisfactorily be estimated from the global solar irradiance as long as seasonal variations are taken into account.