Development and Validation of a New Calibration Model for Diviner 2000® Probe Based on Soil Physical Attributes

This study aimed to develop a new model, valid for soil with and without expandable characters, to estimate volumetric soil water content (θ) from readings of scaled frequency (SF) acquired with the Diviner 2000® sensor. The analysis was carried out on six soils collected in western Sicily, sieved at 5 mm, and repacked to obtain the maximum and minimum bulk density (ρb). During an air-drying process SF values, the corresponding gravimetric soil water content (U) and ρb were monitored. In shrinking/swelling clay soils, due to the contraction process, the variation of dielectric permittivity was affected by the combination of the mutual proportions between the water volumes and the air present in the soil. Thus, to account for the changes of ρb with U, the proposed model assumed θ as the dependent variable being SF and ρb the independent variables; then the model’s parameters were estimated based on the sand and clay fractions. The model validation was finally carried out based on data acquired in undisturbed monoliths sampled in the same areas. The estimated θ, θestim, was generally close to the corresponding measured, θmeas, with Root Mean Square Errors (RMSE) generally lower than 0.049 cm3 cm−3, quite low Mean Bias Errors (MBE), ranging between −0.028 and 0.045 cm3 cm−3, and always positive Nash-Sutcliffe Efficiency index (NSE), confirming the good performance of the model

Modeling for the design of a micro-irrigation system using branched microtubes

Este trabalho foi realizado com o objetivo de se modelar e avaliar o comportamento hidráulico de microtubos ramificados, com base na relação entre vazão e comprimento dos microtubos para uma pressão de entrada, operando sob regime laminar. Dois modelos matemáticos foram estudados, em que um considerou a perda localizada de carga no dimensionamento dos microtubos ramificados e o outro a desconsiderou. O experimento para validação dos modelos foi conduzido no Laboratrio de Hidráulica da Escola Superior de Agricultura "Luiz de Queiroz" (ESALQ-USP), Piracicaba, SP, medindo-se a vazão dos emissores para as pressões de 14,7; 18,6; 39,2 e 58,9 kPa. A configuração do sistema de irrigação consistiu de uma linha lateral com diâmetro nominal (DN) de 10,0 mm, na qual foram inseridos microtubos conectores com DN de 0,8 mm conectados a um segmento de tubo de derivação e acoplados seis microtubos emissores com DN de 0,7 mm. Verificou-se que, dentre os modelos matemáticos, aquele que considerou a perda localizada de carga apresentou maior exatidão pois teve elevado, um bom índice de Willmott e baixo erro quadrático médio

Micro-sprinkler with microtube emitters: a new trickle irrigation hydraulic concern

O microtubo é um emissor simples, de baixo custo, com a grande vantagem de melhor adaptação em condições de topografias onduladas e montanhosas, onde a pressão na linha lateral varia consideravelmente. Este estudo constitui a elaboração de um modelo para dimensionamento hidráulico de microaspersores, cujo emissor é um microtubo de tamanho variável. O fundamento teórico do estudo baseia-se na premissa da compensação da perda de carga na linha lateral e das diferenças topográficas do terreno, através da variação do comprimento do microtubo. Os objetivos específicos deste trabalho foram: determinar as características hidráulicas do microtubo; desenvolver um modelo para dimensionamento do sistema de irrigação proposto e sugerir um defletor para o microaspersor; avaliar a uniformidade de vazão ao longo de linhas laterais experimentais em declive e desenvolver uma planilha eletrônica, para dimensionamento de microtubos. Dois microtubos de diferentes diâmetros foram utilizados neste estudo. Entre as características hidráulicas determinadas, estão o diâmetro interno real, relação vazão-pressão e pressão-comprimento. A determinação do diâmetro interno médio dos microtubos foi realizada em laboratório através da medida de fluxo sob regime laminar e pelo projetor ótico de perfil. Uma equação resultante da combinação das equações de energia desenvolvida por Bernoulli e Darcy-Weisbach além da equação de Hagen-Poiseuille para cálculo do fator de atrito (f), foi deduzida para cálculo do diâmetro. Uma bancada de ensaios foi montada para realização dos ensaios. Os experimentos foram realizados numa faixa de número de Reynolds entre 8000 e 17000, portanto regime de escoamento turbulento. A equação de Darcy-Weisbach foi utilizada para cálculo da perda de carga total e a equação de Blasius foi utilizada para cálculo do fator de atrito (f). Duas laterais foram dimensionadas e instaladas em diferentes declividades (0,5 e 2,3 %). Medidas de dispersão foram utilizadas para avaliar e classificar o sistema de irrigação. Dois modelos de defletores foram desenvolvidos em laboratório, e avaliados em termos de distribuição espacial da água e facilidade construtiva. A análise dos resultados experimentais foi realizada em bases empíricas e teóricas. A avaliação hidrodinâmica do diâmetro dos microtubos aproximou-se muito da determinação através do projetor ótico de perfil, o que indica ser uma alternativa viável para o dimensionamento. A estimativa da pressão de operação do microaspersor baseada nas equações propostas foi bem próxima à pressão observada. O modelo empírico estimou o comprimento do microtubo em função da pressão com bastante precisão, consequentemente a uniformidade de vazão ao longo da lateral foi classificada como excelente em ambas as situações de declive, com coeficientes superiores a 95 %. Uma análise de sensibilidade para estimar as implicações no desempenho hidráulico do sistema, dos erros ou das mudanças nas variáveis envolvidas no dimensionamento, mostrou que o desempenho do emissor é extremamente sensível ao diâmetro do microtubo. Baseado nos resultados obtidos com os ensaios de distribuição pode-se afirmar que é necessário um maior aprofundamento no projeto do defletor do microaspersor. Em geral, a metodologia proposta oferece a possibilidade de ajustar quaisquer variações na carga de pressão ou na topografia do terreno e assim, obter vazão constante ao longo da linha lateral.The microtube is a simple and cheap emitter which has advantage of be suitable for undulating and hilly conditions, where pressure in the lateral line varies considerably. This study aims to develop an empirical approach to the design of a novel micro-sprinkler that uses microtube as the emitters whose length is variable. The theoretic concern is the irrigation system should be designed to compensate variations along lateral line as a function of the friction loss and elevation. General objectives were: hydraulic characterization of the microtube; empiric equations to design; to develop a kind of deflector; to evaluate application uniformity for micro-sprinkler and to do a worksheet to design this system. The relationship between discharge, pressure, and length for microtube emitters of two different diameters were done. The diameter was measured based on flow measurements under laminar flow condition and by accurate optical equipment. Combination of the energy (Bernoulli) and Darcy-Weisbach equations and Hagen-Poiseuille equation (friction factor laminar flow) gives the diameter. A test table to do tests was built. The range of Reynolds numbers during the experiment was 8,000 to 17,000, then turbulent flow. The friction head losses were calculated using the Darcy-Weisbach equation and the friction factor by Blasius equation. Two experimental lines were designed and laid on different slopes (0.5 % and 2.3 %). To evaluate the uniformity of application of water, dispersion measures are used. Two deflectors were created and tested in the laboratory by spatial distribution analysis and easily to manufacture. The data was analyzed by theoretical and empirical approaches. The diameter values of the microtubes were very close to those by optical equipment, then it is a good alternative method to determinate the diameter of the microtube. The pressure observed values were very close to estimated. The empirical approach determined the length required for the microtube emitters with high accuracy, consequently the flow rate uniformity along lateral line was excellent for both laterals, their uniformity coefficients were above 95%. A sensitivity analysis to estimate the implications of errors or changes in key variables on the hydraulic performance of this system showed that the emitter performance is particularly sensitive to the emitter diameter. The deflector tests results showed low spatial uniformity, so we can say that it is necessary more studies at this part of this micro-sprinkler. Finally, the methodology proposed allow adjust any head pressure or elevation variations to high uniformity along of lateral line

Characterisation of the micro-tube emitters used in a novel micro-sprinkler

The microtube is a simple and cheap emitter that was widely used throughout the world in the early days of drip irrigation. Its length can be adjusted according to the pressure distribution along the lateral line and the discharge from the microtube can be adjusted by its length. This not only counters the pressure loss due to pipe friction but also makes it suitable for undulating and hilly conditions, where pressure in the lateral line varies considerably according to the differences in elevation. This is the major problem facing the designer, i.e., emitter flow changes as the acting pressure head changes. In this study, a novel micro-sprinkler system is proposed that uses microtube as the emitter and where the length of the microtube can be varied in response to pressure changes along the lateral to give uniformity of emitter discharges. The objective of this work is to develop and validate empirical and semi-theoretical equations for the emitter hydraulics. Laboratory testing of two microtube emitters of different diameter over a range of pressures and discharges was used in the development of the equations relating pressure and discharge, and pressure and length for these emitters. The equations proposed will be used in the design of the microsprinkler system, to determine the length of microtube required to give the nominal discharge for any given pressure. The semi-theoretical approach underlined the importance of accurate measurements of the microtube diameter and the uncertainty in the estimation of the friction factor for these tubes

Evaluation of air temperature estimated by ERA5-Land reanalysis using surface data in Pernambuco, Brazil

This study aimed to analyze the average air temperature data estimated by ERA5-Land reanalysis over 10 years (01/01/2011 to 12/31/2020), based on data from 12 automatic weather stations located in different cities in the state of Pernambuco, northeast of Brazil. For more careful evaluation, the average air temperature data were stratified by mesoregions of the state. ERA5-Land reanalysis data were validated using statistical indices that evaluated the accuracy. The average air temperature estimated by ERA5-Land reanalysis agree well with weather stations in almost the entire state of Pernambuco. The highest accuracy of the average air temperature estimated by ERA5-Land occurred in the city of Ibimirim (R-2 = 0.98), while the lowest accuracy was measured in the city of Caruaru (R-2 = 0.57). Root-mean-square error (RMSE) generated by the ERA5-Land reanalysis was lower than 0.60 degrees C in most Pernambuco. The highest RMSE of ERA5-Land for average air temperature was calculated using data from the city of Caruaru (1.11 degrees C), whereas the lowest RMSE was obtained with data from the city of Recife (0.41 degrees C). According to mean bias errors, (MBE) the ERA5-Land underestimated the average air temperature data compared to automatic weather stations data, especially in Ouricuri, which had the highest underestimation (-0.80 degrees C). On the other hand, among the municipalities where ERA5-Land overestimated the temperature values, the highest overestimation was identified in Garanhuns (0.35 degrees C). Therefore, based on the results of this study, ERA5-Land reanalysis successfully estimated the average air temperature for the state of Pernambuco

Assessing different methodologies for irrigation scheduling in protected environment: a case study of green bell pepper

This research aimed at assessing four different methodologies to estimate daily irrigation depth, based on the monitoring of soil water status (soil water content sensors, SWS, and tensiometers, TS) and atmospheric evaporative demand (weighing lysimeter, WL, and Piché evaporimeter, PE), of green bell pepper Capsicum annum L.) cultivated in a greenhouse. Furthermore, two different strategies to apply the daily irrigation depths, i.e., single watering (at 8:00 a.m.) or split into two equal applications (at 8:00 a.m. and at 4:30 p.m.), were also investigated. The experiment was conducted in a completely randomized design and according to a 4 × 2 factorial scheme with eight replications. The statistical analysis showed that total water volume (TWV), commercial yield, and crop water use efficiency (WUE) were influenced by the method used to estimate crop water requirement and the irrigation strategies. The TWV applied during the whole crop cycle was 562.7 mm, 731.2 mm, 769.4 mm, and 843.1 mm for treatments with WL, PE, SWS, and TS, respectively. The highest commercial yield was obtained in treatments in which the highest irrigation depth was applied (SWS, 11.55 t ha-1, and TS, 10.09 t ha-1). On the other hand, relatively higher WUE was achieved in treatments managed with SWS (1.63 kg m-3) and WL (1.55 kg m-3). Splitting the estimated daily irrigation depth into two applications promoted the commercial productivity and WUE (9.24 t ha-1 m-3) ha-1 and 1.60 kg compared to the single application (7.06 t and 1.22 kg m-3). Splitting the daily irrigation depth is, therefore, a promising strategy to increase WUE for green bell pepper crops in protected environments

Calibration of two capacitive soil moisture sensors in Ultisol

The objectives of this study were to perform the calibration and determine the calibration equations of two ECH2O soil moisture sensors, for an Ultisol, collected in the Municipality of Pesqueira-PE located in Brazilian semi-arid region. The study was carried out in 5-liter plastic containers in a protected environment at the Federal Rural University of Pernambuco, Recife-PE, where soil moisture was daily monitored for 51 days from saturation moisture to natural drying. The authors verified that the ECH2O sensors showed an exponential response to the variation of soil moisture, obtaining R2>0.97. RMSE values ranged from 0.065 to 0.012 m3 m-3 for the 5TE sensor and from 0.045 to 0.011 m3 m-3 for the EC-5 sensor. The researchers concluded that the calibration equations obtained were more accurate than the factory equations for that type of soilLos objetivos de este estudio fueron realizar la calibración y determinar las ecuaciones de calibración de dos sensores de humedad de suelo ECH2O para un suelo Ultisol colectado en el Municipio de Pesqueira-PE, localizado en el Semiárido Brasileño. El estudio se llevó a cabo en baldes plásticos de 5 litros implementados en ambiente protegido en la Universidad Federal Rural de Pernambuco, Recife-PE, donde se realizó el monitoreo diario de la humedad del suelo durante 51 días, desde la humedad de saturación hasta el secado natural. Los autores verificaron que los sensores ECH2O presentaron una respuesta exponencial a la variación de humedad de suelo obteniendo R2>0,97. Valores de RMSE variaron de 0,065 a 0,012 m3 m-3 para el sensor 5TE y de 0,045 a 0,011 m3 m-3 para el EC-5. Los investigadores concluyeron que las ecuaciones de calibración obtenidas fueron más precisas que las ecuaciones de fábrica para ese tipo de suel

Comparison of meteorological data, related to reference evapotranspiration, from conventional and automatic stations in the Sertão and Agreste regions of Pernambuco, Brazil

The objective was to perform a comparative study of the meteorological elements data that most cause changes in the reference Evapotranspiration (ETo, mm) and its own value, of automatic weather stations AWS and conventional weather stations CWS of the Sertão and Agreste regions of Pernambuco State. The ETo was calculated on a daily scale using the standard method proposed by the Food and Agriculture Organization (FAO), Penman-Monteith (FAO-56). The ETo information obtained from AWS data can be used to update the weather database of stations, since there is a good relationship between the ETo data obtained from CWS and AWS, statistically determined by the Willmott's concordance index (d > 0.7). The observed variations in the weather elements: air temperature, relative humidity, wind speed, and global solar radiation have not caused significant changes in the ETo calculationObjetivo fue realizar un estudio comparativo de los datos de los elementos meteorológicos que más causan cambios en la Evapotranspiración de referencia (ETo, mm) y su propio valor, de EMC y EMA de las regiones de Sertão y Agreste de Estado de Pernambuco. La evapotranspiración de referencia (ETo, mm) se calculó a escala diaria utilizando el método estándar propuesto por la Organización de las Naciones Unidas para la Agricultura y la Alimentación (FAO), Penman-Montheith (FAO-56). La información ETo obtenida de los datos de AWS se puede utilizar para actualizar la base de datos meteorológicos de las estaciones, ya que existe una buena relación entre los datos de ETo obtenidos de EMC y EMA, determinado estadísticamente por el índice de concordancia de Willmott (d > 0,7). Las variaciones observadas en los elementos climáticos: temperatura del aire, humedad relativa, velocidad del viento y radiación solar global no han causado cambios significativos en el cálculo de ET

FDR ECH2O sensor performance in Spodosols

Frequency domain reflectometry (FDR) is widely used to measure the soil water contents. However, the soil composition effects on FDR calibration has to be quantified to reduce the need for further calibration. Our objectives were to (1) evaluate the accuracy of EC-5 for measuring soil water content in sandy soils and (2) develop soil-specific sensor calibration curve. Disturbed and undisturbed soil samples were collected in a Sopossol profile (07º 37’ 30’’ S, 34º 57’ 30’’ W) representative of region sugarcane grown, in northeast of Brazil. Regression statistics analysis showed good accuracy and RMSE = 0.01 m3 m-3, while without specific calibration the RMSE = 0.06 m3 m-3. The EC-5 sensor should be subjected to field-specific calibration in sandy soils due to the low field capacity and water content during the growing seasonLa Reflectometría en el dominio de frecuencia (FDR) es ampliamente utilizada para medir el contenido de agua en el suelo. Sin embargo los efectos de la composición del suelo en la calibración de FDR deben cuantificarse para reducir la necesidad de una calibración adicional. Los objetivos fueron (1) evaluar la precisión del sensor EC-5 para medir el contenido de agua del suelo en suelos arenosos y (2) desarrollar la curva de calibración del sensor específica del suelo. Se colectaron muestras de suelo disturbadas y no disturbadas en el perfil de suelo de Espodosuelo (07º 37’ 30’’ S, 34º 57’ 30’’ W) en um area representantiva de la región productora de caña de azúcar, en el Noreste de Brasil. Los resultados del análisis de regresión mostraron una buena precisión y la RMSE = 0.01 m3 m-3,mientras que sin calibración específica la RMSE = 0.06 m3 m-3. El sensor EC-5 debe someterse a calibración específica en suelos arenosos debido a la baja capacidad de campo y contenido de agua en el periodo de crecimiento

FDR ECH2O sensor performance in Spodosols

Frequency domain reflectometry (FDR) is widely used to measure the soil water contents. However, the soil composition effects on FDR calibration has to be quantified to reduce the need for further calibration. Our objectives were to (1) evaluate the accuracy of EC-5 for measuring soil water content in sandy soils and (2) develop soil-specific sensor calibration curve. Disturbed and undisturbed soil samples were collected in a Sopossol profile (07º 37’ 30’’ S, 34º 57’ 30’’ W) representative of region sugarcane grown, in northeast of Brazil. Regression statistics analysis showed good accuracy and RMSE = 0.01 m3 m-3, while without specific calibration the RMSE = 0.06 m3 m-3. The EC-5 sensor should be subjected to field-specific calibration in sandy soils due to the low field capacity and water content during the growing season