Projeto, instalação e calibração de um lisímetro de pesagem para estudos de evapotranspiração de culturas agrícolas

Lysimeters are tanks filled with soil commonly used in studies of crop ET and movement of water and chemicals in the soil profile. The objective of this work is to describe the procedures for construction, installation and calibration of a precision weighing lysimeter for water demand studies of Sumatra type tobacco (Nicotiana tabacum L.) in Bahia, Brazil. The lysimeter was 1.60 m long, 1.10 m wide and 0.60 deep, with an internal soil surface of 1.76 m2. The lysimeter was installed in an area covered by a 30% shading screen used specifically for production of this type of tobacco. The inner box of the lysimeter was made of steel plates and the outer box was built on site with burnt-clay bricks bonded with cement mass. The weighing platform comprised four 1,000 kg capacity load cells placed underneath the inner tank and a datalogger for data recording. The lysimeter was calibrated in the field using standard loads of known mass. Five cycles of loading and unloading were performed (47 points) in the range of 0 to 110 kg (62.5 mm). The system showed a strong linear relationship between standard mass and load cells output (r2 > 0.99 and Sy/x = 0.033 mm). The load cell accuracy, which combines the effects of hysteresis, linearity and repeatability errors, was found to be of the order of ±0.06 mm and the datalogger was found to be able to resolve mass changes less than 0.1 mm. These uncertainty parameters combined with the ability of the lysimeter to respond to relatively small mass changes suggest that the weighing lysimeter herein described is adequate to measure tobacco ET over time periods of one hour or longer. The investment was around US$5,100.00, including hardware and field work for installation.Lisímetros são tanques preenchidos com solo comumente utilizados em estudos de ET das culturas e movimento da água e solutos no perfil do solo. O objetivo deste trabalho é descrever os procedimentos de construção, instalação e calibração de um lisímetro de pesagem para estudo da demanda de água do fumo (Nicotiana tabacum L.) tipo Sumatra, na Bahia, Brasil. O lisímetro, com área interna de 1,76 m2, tinha 1,10 m de largura, 1,60 m de comprimento e 0,60 m de profundidade e foi instalado em área comercial de fumo coberta com tela de sombreamento de 30$ 5.000,00, incluindo equipamento e mão de obra para instalação

Fluxes of Energy and Water Vapour from Grazed Pasture on a Mineral Soil in the Waikato

The eddy covariance (EC) technique was used to measure half hourly fluxes of energy and evaporation from 15 December 2007 to 30 November 2008 at the Scott Research Farm, located 7 km east of Hamilton. Many other supporting measurements of climate and soil variables were also made. The research addressed three objectives: 1. To examine the accuracy of the eddy covariance measurement technique. 2. Understand the surface partitioning of energy and water vapour on a diurnal to annual timescale. 3. Compare measurements of evaporation to methods of estimation. Average energy balance closure at Scott Farm was deficient by 24%, comparable to published studies of up to 30%. Three lysimeter studies were carried out to help verify eddy covariance data. These resulted in the conclusions that; 1) lysimeter pots needed to be deeper to allow for vegetation rooting depths to be encompassed adequately; 2) forcing energy balance closure was not supported by two of the studies (summer and winter); 3) latent heat flux (λE) gap filling of night time EC data during winter over estimated values by about 10 W m-2; and 4) the spring lysimeter study verified eddy covariance measurements including the closure forcing method. Some uncertainty still exists as to the accuracy of both lysimeter and EC methods of evaporation measurement because both methods still have potential biases, however for the purpose of this study, it would appear data are sufficiently accurate to have confidence in results. Energy and water vapour fluxes varied on both a diurnal and seasonal timescale. Diurnally, fluxes were small or negative at night and were highest during the day, usually at solar noon. Seasonally, spring and summer had the highest energy and evaporation fluxes and winter rates were small but tended to exceed available energy supply. Evaporation was constrained by soil moisture availability during summer and by energy availability during winter. Estimated annual evaporation at Scott Farm was 755 mm, 72% of precipitation. Two evaporation models were compared to eddy covariance evaporation (EEC) measurements; the FAO56 Penman-Monteith model (Eo) and the Priestley-Taylor model (EPT). Both models over estimated evaporation during dry conditions and slightly under estimated during winter. The α coefficient that is applied to EPT was not constant and a seasonally adjusted value would be most appropriate. A crop coefficient of 1.13 is needed for Eo measurements during moist conditions. Eo began over estimating evaporation when soil moisture contents dropped below ~44%. A water stress adjustment was applied to both models which improved evaporation estimates, however early onset of drying was not able to be adjusted for. The adjusted Eo model is the most accurate overall, when compared to EEC

Modelling the water balance of a grassland soil

Expected future climate change characterized by higher temperatures and more frequent summer droughts may cause significant changes in soil hydrological processes leading to limited nutrient and water availability and reductions in plant growth. Soil hydrological and plant growth models attempt to reproduce the complex interactions in the plant-soil water system in terms of mathematical equations, parameters and coefficients. If these models are able to capture the behaviour of the plant-soil-atmosphere continuum, in terms of soil water fluxes in the vadose zone and plant growth, they could help users to understand and predict the effects of climate change. In the scope of this study, a numerical soil water balance model was applied to three soil lysimeters located in Rollesbroich, Germany to analyse the accuracy of model predictions for temperate grassland. The model output showed some differences in calibrated model parameters and goodness-of-fit for the three lysimeters with identical soil profiles. The numerical analysis of the simulated results showed a satisfactory degree of model plausibility with R2 values between 0.52 and 0.99, RMSE between 0.01 and 0.05 cm3 cm-3 for water contents and 0.067 to 0.072 cm d-1 for actual evapotranspiration. The graphical model analysis showed a good explanation of the main seasonal patterns in the observations, despite some errors revealed by an analysis of the model residuals. It can be concluded that, with some additional improvements, this soil hydrological model could be applied to simulate the effects of future climate change scenarios

Considering soil water content, nutrients movement, phenology and plant growth with reference to development of functional foods in a lysimeter study

Lysimeter is equipped with mechanisms for weighing by load cells enable automated measurements, and the signals resulting from weight changes in the system due to evaporation that are generally recorded in a data acquisition system. According to methods of measuring water content, lysimeters may be divided into weighing lysimeter and non-weighing lysimeter. The weighing lysimeters provide scientists the basic information for research related to evapotranspiration, and they are commonly divided into two types, continuous weighing and intermittent weighing. Weighing lysimeters have been used to quantify precipitation (P) not only in the form of rain or snow, but also dew, fog and rime, and also to determine actual evapotranspiration (ET). Compared to laboratory experiments, out-door lysimeter studies have advantages, like being closer to field environment conditions, it is possible to grow plants and therefore to study the fate of chemicals in soil/plant systems, transformations and leaching. The limitations are costy, which depend on design, variable experimental conditions, such as environmental/ climatic parameters, which are normally not controlled, the soil spatial variability is normally less, they are not suitable for every plant species and even every soil type. The objective of lysimeter is defining the crop coefficient (Kc), which used to convert ETr into equivalent crop evapotranpiration (ETc) values, and determing agronomical characteristics of crops, which are planted in the field of lysimeter. The duration of a lysimeter study is determined by the objective of the study, but for different crops, it should normally be at least two years. Weighing lysimeters using load cells have the advantage of measuring the water balance in the soil over a short time and with good accuracy. Precipitation should be recorded daily at the lysimeter site. All weather data like air temperature, solar radiation, humidity and potential evporation should be obtained onsite, and the frequency and time of measurements should be at least daily

Temporal Variability In The Daytime Green Roof Energy Balance During Drying Periods

Green roofs are a building design element intended to increase evaporative cooling in cities during the summer, which helps alleviate the daytime impacts of heat on human health and energy consumption, and supports mitigation and adaptation to the local effects of climate change. Time varying energy balances were measured on a 0.15 m deep, ~ 60 m2 modular green roof with Sedum spurium in London, Ontario for the summer of 2014. A lysimetry approach was used to measure latent heat QE. Net radiation Q* and ground heat flux QG were also measured, with sensible heat flux QH derived as a residual. An empirical model of evaporative flux ratio QE/(Q*-QG) by volumetric water content VWC was fit based on experimental data (typical values ranged from 0.2-0.4 and decreased linearly to 0.05 during atypical low VWC below 0.22). Research presented here can inform future optimization of green roof atmospheric cooling performance. Furthermore, this study indicates that green roof atmospheric cooling performance in typical North American mid latitude climates is lower than typical urban greenery such lawns and parks, which has policy implications for sustainable building design and urban planning

Direct determination of crop evapotranspiration in the Arkansas Valley with a weighing lysimeter

January 2011.Includes bibliographical references

The Effect of Watering Regimes on the Growth and Development of Alpinia Purpurata (Viell) K. Schum. Inflorescences

The objective of this research was to determine the water requirement of Alpinia purpurata (red ginger) to produce high quality inflorescences. A farm using overhead irrigation with impact sprinklers at 4.3 mm per hour for one hour three times per week proved superior to the drip irrigated three cultivars of Alpinia purpurata, red ginger, 'Eileen McDonald', and Ginoza No.__, were grown under different irrigation levels at the Waimanalo Research Station located in Waimanalo, Hawaii from August 1991 to May 1993. Five drip-irrigation treatments corresponded to replacement of 0.33 to 1.67 of pan evaporation. Weekly samples of the shoots were monitored to determine the stages of growth and development of the plant. The stages of inflorescence development in chronological order were: inflorescence initiation, appearance of color at the shoot tip, swelling of the inflorescence, appearance of the inflorescence, and harvest of the shoot. The influence of water application rates was monitored by stomatal conductance, relative water content, total leaf area per shoot, inflorescence diameter and length, shoot diameter and length, number of expanded leaves, and number of inflorescences per clump. Seasonal trends were compared with environmental data collected by a weather station. The components of the soil water balance were determined. The stages of inflorescence development were not affected by water application rates but were affected by the cultivars and seasonality. The average durations (weeks) for the appearance of color at the shoot tip, swelling of the inflorescence, appearance of the inflorescence, and harvest of the shoot were 20.8, 21.5, 23.2, and 26.4 respectively. The Ginoza cultivar took significantly longer from shoot emergence to all four stages compared to the other two cultivars. The Ginoza cultivar also produced the longest shoots, most number of expanded leaves, and shorter inflorescences than 'Eileen McDonald'. Shoots which emerged at the start of increasing temperatures and solar radiation (March and April) averaged shorter times to the four stages compared to shoots which emerged at the start of decreasing temperature and solar radiation (November). The highest irrigation treatment produced higher quality inflorescences, but all treatments appeared to experience frequent water stress due to deep drainage

Evaluation of crop coefficient and evapotranspiration data for sugar beets from landsat surface reflectances using micrometeorological measurements and weighing lysimetry

In California and other agricultural regions that are facing challenges with water scarcity, accurate estimates of crop evapotranspiration (ETc) can support agricultural entities in ongoing efforts to improve on-farm water use efficiency. Remote sensing approaches for calculating ETc can be used to support wide area mapping of crop coefficients and ETc with the goal of increasing access to spatially and temporally distributed information for these variables, and advancing the use of evapotranspiration (ET) data in irrigation scheduling and management. We briefly review past work on the derivation of crop coefficients and ETc data from satellite-derived vegetation indices (VI) and evaluate the accuracy of a VI-based approach for calculation of ETc using a well instrumented, drip irrigated sugar beet (Beta vulgaris) field in the California Central Valley as a demonstration case. Sugar beets are grown around the world for sugar production, and are also being evaluated in California as a potential biofuel crop as well as for their ability to scavenge nitrogen from the soil, with important potential benefits for reduction of nitrate leaching from agricultural fields during the winter months. In this study, we evaluated the accuracy of ETc data from the Satellite Irrigation Management Support (SIMS) framework for sugar beets using ET data from a weighing lysimeter and a flux station instrumented with micrometeorological instrumentation. We used the Allen and Pereira (A&P) approach, which was developed to estimate single and basal crop coefficients from crop fractional cover (fc) and height, and combined with satellite-derived fc data and grass reference ET (ETo) data as implemented within SIMS to estimate daily ETc from SIMS (ETc-SIMS) for the sugar beet crop. The accuracy of the daily ETc-SIMS data was evaluated against daily actual ET data from the weighing lysimeter (ETa-lys) and actual ET calculated using an energy balance approach from micrometeorological instrumentation (ETa-eb). Over the course of the 181-day production cycle, ETc-SIMS totaled 737.1 mm, which was within 7.7% of total ETa-lys and 3.7% of ETa-eb. On a daily timestep, SIMS mean bias error was −0.31 mm/day relative to ETa-lys, and 0.15 mm/day relative to ETa-eb. The results from this study highlight the potential utility of applying satellite-based fc data coupled with the A&P approach to estimate ETc for drip-irrigated crops