A comparative study of two types of spray sprinklers was performed. Rotating spray plate sprinklers (RSPS) and fixed spray plate sprinklers (FSPS) were evaluated individually in open field conditions. The water distribution, wind drift and evaporation losses during the evaluations were measured under low, medium and high wind speed conditions with three nozzle diameters and two nozzle heights above the soil surface. Individual spray sprinkler water distributions were mathematically overlapped to simulate the water distribution resulting from sprinkler machines. The water distribution of RSPS had a conical shape, while the FSPS concentrated the water application in a circular crown. The uniformity coefficient (CU) of the simulated water application in sprinkler machines fitted with RSPS or FSPS was higher than 93 % in all cases.However, the RSPS could attain higher CU at higher spacing along the lateral. For the nozzle diameters of 6.7 and 7.9 mm, the wetted width produced by the RSPS was larger than that of the FSPS. Also, the peak instantaneous precipitation rate of the RSPS was smaller than that of the FSPS.

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Irrigation is by far the largest consumer of water in the world. At the same time the need for irrigation may differ between different zones of a particular field due to spatial soil variability. In particular total available water content (TAWC) has effects on irrigation frequency and depth. The objective of our study was to compare the ability of two fast, non-destructive and sensor-based apparent soil electrical conductivity (ECa) measurement methods:A contact and electrode-based sensor (VERIS 3100, both shallow and deep modes); A non-contact, electromagnetic induction (EMI)-based sensor (Geonics EM38, both horizontal and vertical orientations) to monitor the within-field variation of the TAWC.The ECa data, standardized to 258C (EC25), were collected on a 1 s interval corresponding to 2-3 m data spacing on transects spaced approximately 4-6 m apart. Based on the ECa spatial variability pattern, and to cover the range of ECa values present, 29 calibration points were located using a differential Global Positioning System (DGPS) to develop field-specific relationships between ECa data and TAWC in the upper 60 cm of soil. However, we found better correlations between TAWC and the VERIS 3100 readings. Calibration equations to estimate TAWC from the shallow mode of VERIS 3100 data exhibited a good fit to the data and had the highest correlation (R 2 ¼ 0.77), whereas calibrations to EM38 data (both vertical and horizontal orientation) were low and apparently could not adequately reflect the spatial variability of the TAWC due to the influence of the more highly variable topsoil. We identified six TAWC zones based on fuzzy k-means unsupervised classification as an optimum number of irrigation management zones within our field (Zone 1: 99-105, Zone 2: 105-116, Zone 3: 116-127, Zone 4: 127-138, Zone 5: 138-149, Zone 6: 149-161 mm per 60 cm). We concluded that under traditional irrigation conditions, Zones 1 and 2 were over-irrigated whereas Zones 4, 5 and 6 were deficit irrigated. Copyright # 2007 John Wiley & Sons, Ltd.key words: precision irrigation; irrigation management zones; total available water content; soil; electrical conductivity Un capteur de contact basé sur électrode (VERIS 3100, modes peu profonds et profonds); Un capteur sans contact, basé sur induction électromagnétique (IEM) (Geonics EM38, orientations horizontales et verticales) pour suivre la variation de la TAWC à travers le champ étudié.Les données d'ECa, normalisées à 258C (EC25), ont été collectées à des intervalles de 1 seconde correspondant à une distance de 2 à 3 mètres sur des transects eux-mêmes espacés d'environ 4 à 6 mètres. En se basant sur le modèle de variabilité spatiale de l'ECa, et pour couvrir la gamme des valeurs d'ECa présentes, 29 points de calibrage ont été localisés à l'aide d'un système différentiel de géo-référencement (DGPS) dans le but d'établir des relations, propres au champ étudié, entre les données d'ECa et la TAWC dans les 60 premiers centimètres du sol. Cependant, les meilleures corrélations ont été trouvées ...

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The purpose of this paper was to assess the feasibility and significance of applying spatially variable irrigation under a central pivot system at the Federal German Agricultural Research Center, Braunschweig, Germany. The assessment was based on soil moisture holding capacity, soil depth variation and root development. Soil texture analysis was carried out by sampling on a 60 meter grid. The German Agro-Meteorological Model was applied to simulate the water balance in the crop-soil-atmosphere system for the growing season 2003/4. The research findings are presented in terms of six scenarios: 20, 30, 40 mm water application depths per irrigation under both variable rate application and uniform application. The comparison revealed that the loss of water was higher for the uniform application scenarios than that for the variable rate application (VRA) scenarios for the applications of 20 and 30 mm. The VRA scenario of 20 mm water application was found out to be the best option for water conservation.

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