Water relations and photosynthesis as criteria for adequate irrigation management in 'Tahiti' lime trees

Irrigation scheduling based on soil moisture status is one of the most useful methods because of its practicality and low cost. The effects of available soil water depletion on evapotranspiration (ETc), transpiration (E), leaf water potential at predawn (psiP) and midday (psiM), stomatal conductance (gs) and net CO2 assimilation (A) in lime 'Tahiti' trees (Citrus latifolia) were evaluated to improve irrigation schedule and minimize water use without causing water stress. The trees were spaced 7 <FONT FACE=Symbol>&acute;</FONT> 4 m and drip-irrigated by four drippers with the available soil water content (AWC) depleted by suspension of irrigation (40 days). Leaf water potential was measured on a pressure chamber (psiP and psiM) and leaf gas exchange was measured by infrared gas analyzer (E, gs and A). Evapotranspiration was determined with the aid of weighing lysimeter. Water soil content and potential (psiS) were monitored with TDR probes and tensiometers, respectively, installed at 0.3, 0.6 and 0.9 m depths. Meteorological variables were monitored with an automatic weather station in the experimental area. The threshold AWC level for the onset of ETc decline was 43%, and 60% for gs, A, E and Y P. Also, psiP was more sensitive to AWC than psiM, and is therefore a better tool for irrigation. When AWC was around 60%, values of psiP and psis were -0.62 MPa and -48.8 kPa, respectively

Water Balance Components in a Mature Citrus Orchard

The low water-holding capacity of sandy soils, together with spatial and temporal variations of rainfall, require Florida citrus trees to be irrigated for optimal production. Citrus tree root systems are exposed to various hydrologic conditions because of soil temperature and water gradients due to tree canopy shading and under-tree microirrigation. The main goal of this study was to evaluate water balance components in a mature citrus orchard grown on central Florida ridge soils with special interest in quantifying rainfall interception by a citrus canopy and its effect on effective rainfall estimation. Soil water content was monitored every 30 min at 10-, 20-, 40-, and 80-cm depths in the root zone both under and outside of citrus tree canopies. Microirrigation, rainfall, and weather data were used to calculate effective rainfall, plant water uptake, and deep drainage. We found that the tree canopy intercepted 35 and 50% of the incoming high (≥5-mm) and low (\u3c5-mm) intensity rainfalls, respectively. Effective rainfall calculated without accounting for the canopy interception effect was overestimated by about 30 and 5% for the dry and wet periods, respectively. Citrus crop evapotranspiration was higher under the tree canopy (irrigated area) than outside the tree canopy (unirrigated area) during the dry season because of supplemental irrigation. © Soil Science Society of America All rights reserved

Estratégias de manejo de água em caupi irrigado Strategies of irrigation scheduling in cowpea

Este trabalho foi conduzido no período de setembro a dezembro de 1997, numa área irrigada da Fazenda Experimental do Vale do Curu, pertencente à Universidade Federal do Ceará, no município de Pentecoste, CE, localizada a 100 km de Fortaleza. O objetivo do experimento foi avaliar a utilização do tensiômetro de mercúrio, do Tanque Classe A e da equação de Hargreaves, na determinação da lâmina de água a ser aplicada na irrigação. O delineamento foi inteiramente casualizado, com três tratamentos e quatro repetições, enquanto os tratamentos foram representados pelos três diferentes métodos de estimação citados, de quando e quanto irrigar (Tratamento 1 - Tensiômetro; Tratamento 2 - Tanque Classe A e Tratamento 3 - equação de Hargreaves) e a cultura utilizada foi o caupi (Vigna unguiculata (L.) Walp) para consumo em estado verde, cultivar João Paulo II, no espaçamento de 0,90 x 0,40 m, com duas plantas por cova, irrigada por aspersão convencional. A análise dos resultados constatou uma economia de água no tratamento 1, de 28 e 23%, em relação aos tratamentos 2 e 3, respectivamente, e também evidenciou a inexistência de diferenças significativas entre as produtividades alcançadas em todos os tratamentos. O tensiômetro pode ser indicado como instrumento de racionalização do uso da água em irrigação.<br>A field study was conducted from September to December 1997 at the Federal University of Ceará Experimental Farm in Pentecoste, Brazil. The irrigation scheduling was based on a tensiometer, Class A pan evaporation and Hargreaves equation. The purpose of the research was to evaluate the three treatments (Treatment 1 - tensiometer, Treatment 2 - pan evaporation and Treatment 3 - Hargreaves equation) with four replications in a completely randomized design. Sprinkler irrigated cowpea (Vigna unguiculata (L.) Walp), cultivar João Paulo II for fresh consumption was grown on the experimental area. Plants were spaced at 0.90 x 0.40 m, maintaining two plants per hole. Crop yield showed no significant difference, although using the tensiometer to schedule irrigation, the water consumption was 28 and 30% lower compared to the Class A Pan Evaporation and Hargreaves equation, respectively. The tensiometer may be indicated as an instrument for saving water in irrigation scheduling

Ocorrência de entupimento de origem biológica em sistema de irrigação por gotejamento Occurrence of cloging of biological origin in drip irrigation

O trabalho consistiu de uma avaliação da uniformidade de distribuição de água em uma parcela de um sistema de irrigação por gotejamento para produção de flores em estufa, com 5 anos de uso, em uma propriedade no município de Atibaia, SP. Em uma amostra de 25 gotejadores retirados da parcela, determinou-se, em laboratório, a curva de vazão-pressão e o coeficiente de variação de fabricação, CV, para as pressões de 50, 100, 150, 200, 250, 300, 350 e 400 kPa. Análises química, física e de contagem bacteriológica da água foram realizadas em três pontos do sistema de irrigação: na fonte de água, após o sistema de filtragem e no final de uma linha de gotejadores no meio da parcela avaliada. O valor do CV foi de 8,2% e os valores de 73% para o coeficiente de uniformidade de aplicação de água, 97% para o coeficiente de uniformidade hidráulica e 26% para o coeficiente de performance do emissor, juntamente com os resultados das análises da água, permitiram evidenciar-se a ocorrência de entupimento de origem biológica afetando a uniformidade de aplicação de água do sistema.<br>An irrigation system used for flower production during five years, in the municipality of Atibaia, SP, Brazil, was evaluated. A sample of 25 used emitters were evaluated in laboratory for discharge pressure curve and manufacturer's variation coefficient at 50, 100, 150, 200, 250, 300, 350 and 400 kPa. Chemical, physical and microbiological water analysis were performed at three different points: water source, after filtration unit and at lateral end. The manufacturer's coefficient was 8.2%. The statistical uniformity of the emitter discharge rates was 73%; the hydraulic uniformity based on pressure distribution was 97% and the emitter performance variation was 26%. Water analysis results along with performance evaluation showed occurrence of emitter cloging causing low statistical uniformity of emitter discharge

Simulação das perdas de água por evaporação e arraste, no aspersor NY-7 (4,6 mm x 4,0 mm), em sistemas de aspersão convencional Simulation of evaporation and wind drift losses, in the NY-7 sprinkler (4.6 mm x 4.0 mm), in stationary sprinler irrigation systems

As perdas de água por evaporação e arraste em sistemas de irrigação por aspersão podem assumir valores consideráveis, reduzindo a eficiência do sistema. Os objetivos do presente trabalho foram avaliar a capacidade preditiva de cinco modelos empíricos para estimar perdas de água por evaporação e arraste em aspersores modelo NY-7 (bocais de 4,6 mm x 4,0 mm), trabalhando sob diferentes condições operacionais e ambientais, e ajustar modelos específicos para o aspersor NY-7. Comparando os resultados medidos em ensaios de campo, com os resultados simulados, foi possível concluir que os cinco modelos empíricos considerados apresentaram pouca ou nenhuma adequação, tanto para os ensaios com um único aspersor (quadrado do erro-médio de 5,27; 20,70; 5,07; 6,95 e 7,06% para os modelos empíricos 1; 2; 3; 4 e 5, respectivamente) quanto para os ensaios com linhas laterais contendo aspersores (quadrado do erro-médio de 7,41; 24,43; 6,72; 3,16 e 2,9% para os modelos empíricos 1; 2; 3; 4 e 5, respectivamente). Comparados aos cinco modelos empíricos considerados, os novos modelos ajustados apresentaram menores erros, indicando que a aplicação de modelos empíricos deve ser limitada às condições de operação (diâmetro de bocal, pressão de operação, etc.) similares àquelas em que os modelos foram desenvolvidos.<br>Evaporation and wind drift losses during sprinkler irrigation may reach significant values, cutting system efficiency down. The present work aims: (a) to evaluate the ability of five empirical models in predicting losses of a NY-7 model sprinkler (nozzle of 4.6 mm x 4.0 mm), working under different operational and climatic conditions; and (b) to adjust specific models to the NY-7 sprinkler. By comparing measured values - obtained on field trials - with simulated ones, it was possible to conclude that, in general, the five considered empirical models presented little or no adjustment for the single-sprinkler outdoor tests (root mean square error of 5.27; 20.70; 5.07; 6.95 and 7.06% for empirical models 1; 2; 3; 4 and 5, respectively) as well as for the block irrigation outdoor tests (root mean square error of 7.41; 24.43; 6.72; 3.16 and 2.90% for empirical models 1; 2; 3; 4 and 5, respectively). When compared to the five considered empirical models, the new adjusted models showed lower errors, indicating that the application of empirical models must be limitated to working conditions (nozzle size, operational pressure, etc.) similar to the ones in which they were developed