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  • 1
    Language: English
    In: Journal of Irrigation and Drainage Engineering, May-June, 2004, Vol.130(3), p.184(8)
    Description: The Hargreaves method enables reference crop evapotranspiration ([ET.sub.0]) estimation in areas where meteorological information is scarce, as, for example, southern Spain. However, this method is known to produce considerable bias in this region, especially during the dry, hot summer months. An evaluation of the method is made by comparing daily estimates with those made by the more commonly recommended Penman-Monteith method at 16 meteorological stations. Computed [ET.sub.0] values at the coastal stations are, on average, 0.69 mm [d.sup.-1] smaller than the Penman-Monteith estimates whereas at inland stations a small average overestimation of 0.13 mm [d.sup.-1] is shown. The adjusted Hargreaves coefficient (AHC), obtained through regression analysis, increases at the coastal stations, on average, to 0.0029, and decreases at the inland stations to 0.0022. Adjustment with the Samani method does generally not produce more accurate estimates in this region. Finally a linear relationship between the AHC and the rate of the average temperature to the average daily temperature range is proposed for the regional adjustment of the Hargreaves coefficient. CE Database subject headings: Evapotranspiration; Calibration: Spain; Crops; Irrigation practices.
    Keywords: Irrigation Engineering -- Research
    ISSN: 0733-9437
    E-ISSN: 19434774
    Source: Cengage Learning, Inc.
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  • 2
    Language: English
    In: Journal of Hydrology, October 2015, Vol.529, pp.1713-1724
    Description: The application of simple empirical equations for estimating reference evapotranspiration (ET ) is the only alternative in many cases to robust approaches with high input requirements, especially at the local scale. In particular, temperature-based approaches present a high potential applicability, among others, because temperature might explain a high amount of ET variability, and also because it can be measured easily and is one of the most available climatic inputs. One of the most well-known temperature-based approaches, the Hargreaves (HG) equation, requires a preliminary local calibration that is usually performed through an adjustment of the HG coefficient (AHC). Nevertheless, these calibrations are site-specific, and cannot be extrapolated to other locations. So, they become useless in many situations, because they are derived from already available benchmarks based on more robust methods, which will be applied in practice. Therefore, the development of accurate equations for estimating AHC at local scale becomes a relevant task. This paper analyses the performance of calibrated and non-calibrated HG equations at 30 stations in Eastern Spain at daily, weekly, fortnightly and monthly scales. Moreover, multiple linear regression was applied for estimating AHC based on different inputs, and the resulting equations yielded higher performance accuracy than the non-calibrated HG estimates. The approach relying on the ratio mean temperature to temperature range did not provide suitable AHC estimations, and was highly improved by splitting it into two independent predictors. Temperature-based equations were improved by incorporating geographical inputs. Finally, the model relying on temperature and geographic inputs was further improved by incorporating wind speed, even just with simple qualitative information about wind category (e.g. poorly vs. highly windy). The accuracy of the calibrated and non-calibrated HG estimates increased for longer time steps (daily 〈 weekly 〈 fortnightly 〈 monthly), although with a decreasing accuracy improvement rate. The variability of goodness-of-fit between AHC models was translated into lower variability of accuracy between the corresponding HG calibrated ET estimates, because a single AHC was applied per station. The AHC fluctuations throughout the year suggest the convenience of using monthly or, at least, seasonal models.
    Keywords: Reference Evapotranspiration ; Hargreaves Equation ; Temperature-Based ; Limited Inputs ; Geography
    ISSN: 0022-1694
    E-ISSN: 1879-2707
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  • 3
    Language: English
    In: Journal of Hydrology, Feb 25, 2013, Vol.481, p.106(13)
    Description: To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.jhydrol.2012.12.024 Byline: Gonzalo Martinez (a)(b), Yakov A. Pachepsky (b), Harry Vereecken (c), Horst Hardelauf (c), Michael Herbst (c), Karl Vanderlinden (d) Keywords: Soil water content; Temporal stability; Simulations; Local controls; Saturated hydraulic conductivity Abstract: a* We simulated soil water flow in bare and grassed soil columns of three textures. a* Typical features of soil water temporal stability were recovered in simulations. a* Simulated duration and season affected the temporal stability of soil water contents. a* Spatio-temporal variations in soil water correlated with soil hydraulic conductivity. Author Affiliation: (a) Dept. of Agronomy, University of Cordoba, 14071 Cordoba, Spain (b) USDA-ARS- Environmental Microbial and Food Safety Lab, Beltsville, MD 20705, USA (c) Agrosphere (IBG-3), Institute of Bio- and Geosciences, Forschungszentrum Julich GmbH, 52428 Julich, Germany (d) IFAPA, Centro Las Torres-Tomejil, 41200 Alcala del Rio, Spain Article History: Received 15 December 2011; Revised 14 December 2012; Accepted 17 December 2012 Article Note: (miscellaneous) This manuscript was handled by Corrado Corradini, Editor-in-Chief, with the assistance of Axel Bronstert, Associate Editor
    Keywords: Hydrogeology -- Models ; Food Safety -- Models ; Soil Moisture -- Models ; Hydraulic Flow -- Models ; Water -- Models
    ISSN: 0022-1694
    Source: Cengage Learning, Inc.
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  • 4
    Language: English
    In: Plant and Soil, 2014, Vol.384(1), pp.381-400
    Description: Background and aims Future success of olive cropping in the Mediterranean depends critically on improving yield, reducing production costs, and preventing infestation by soil-borne pathogens. In order to put forward adequate soil management practices accurate knowledge of the spatial distribution of soil properties is required. The aims of this study were to delimit areas with constrained tree development in an olive orchard using electromagnetic induction (EMI), and to identify the causal relationships between apparent electrical conductivity (ECa) and soil properties. Methods The experimental field was exhaustively sampled for different soil properties and ECa was measured in 2011 and 2012 under dry and wetter soil conditions, respectively. Results The spatial ECa distribution matched the observed canopy coverage pattern well. Three zones were delimited according to ECa values from 0 to 27.5, from 27.5 to 57.5, and greater than 57.5 mS [m.sup.-1]. All ECa signals, regardless of soil-water status, exhibited a common dominant ECa pattern. The area with the lowest ECa values (0-27.5 mS [m.sup.-1]) showed optimal tree growth (45% canopy coverage) and presented significantly lower average clay contents than the other two areas. Intermediate ECa values (27.5-57.5 mS [m.sup.-1]) identified accurately the area with deficient tree development and tree die-off (12% canopy coverage), and corresponded with an area along the drainage pathway where profile-averaged soil-water, clay, stone and organic matter content were highest. Conclusions EMI surveys detected subtle differences in soil properties and provided useful information to delimit areas with constrained tree development. The approach can be used as a screening technique before installing tree plantations. Keywords Olive * Soil-borne pathogens * Apparent electrical conductivity * Soil management * Vertisol * Soil water content
    Keywords: Olive ; Soil-borne pathogens ; Apparent electrical conductivity ; Soil management ; Vertisol ; Soil water content
    ISSN: 0032-079X
    E-ISSN: 1573-5036
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  • 5
    Language: English
    In: Journal of Hydrology, January 2017, Vol.544, pp.319-326
    Description: Knowledge of spatio-temporal soil-water content (SWC) variability in agricultural fields is useful for improving crop management. Spatial patterns of SWC can be characterized using temporal stability analysis of difficult-to-obtain data from high spatial density and temporal frequency. Soil apparent electrical conductivity (ECa) measurements with high spatial density have been widely used to infer the spatial variability of SWC. The objective of this work is to test the hypothesis that temporal stability of ECa can be demonstrated and that relationships between temporal stability characteristics of SWC and ECa can be established. Apparent electrical conductivity and topsoil gravimetric SWC ( ) were periodically measured in an olive orchard in southwest Spain on 6 and 18 occasions, respectively. A temporal stability analysis of ECa elucidated three zones where ECa was close to, consistently substantially smaller than, and substantially larger than the spatial average ECa throughout the study period. Representative locations for were found with a chance of 75% within the representative zone for ECa. Yet, the driest locations, with consistently smaller than the field average ( ), could be successfully identified (89%) within the zone with consistently smaller ECa than average. The − relations showed generally a linear behaviour, although a better fit was obtained at the highest using either exponential or power law equations at half of the locations. The former provided the best fit within the zone with ECa consistently smaller than average, while the latter performed best in the zone with ECa consistently larger than average. The linear equation provided the best fit within the representative ECa zone. This study demonstrates that temporal stability characteristics of ECa and SWC are linked and that ECa surveys can be used to delimit zones with representative locations for SWC measurement or estimation. Such information is of importance for a range of agricultural applications, . irrigation, crop protection, fertilizer management, and soil and water conservation.
    Keywords: Soil-Water Content ; Apparent Electrical Conductivity ; Temporal Stability ; Soil Spatial Classification ; Geography
    ISSN: 0022-1694
    E-ISSN: 1879-2707
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  • 6
    Language: English
    In: Journal of Hydrology, 25 February 2013, Vol.481, pp.106-118
    Description: ► We simulated soil water flow in bare and grassed soil columns of three textures. ► Typical features of soil water temporal stability were recovered in simulations. ► Simulated duration and season affected the temporal stability of soil water contents. ► Spatio-temporal variations in soil water correlated with soil hydraulic conductivity. Occurrence of temporal stability of soil water content has been observed for a range of soil and landscape conditions and is generally explained as a consequence of local and non-local controls. However, the underlying factors for this phenomenon are not completely understood and have not been quantified. This work attempts to elucidate and quantify the effects of several local controls, such as soil hydraulic properties and root water uptake, through water flow simulations. One-dimensional water flow was simulated with the HYDRUS code for bare and grassed sandy loam, loam and clay soils at different levels of variability in the saturated hydraulic conductivity . Soil water content at 0.05 and 0.60 m and the average water content of the top 1 m were analyzed. Temporal stability was characterized by calculating the mean relative differences of soil water content in 100 soil columns used for each combination of soil and season. Using log-normal distributions of resulted in mean relative differences distributions that were commonly observed in experimental studies of soil water content variability. Linear relationships were observed between scaling factor of ln and spread of the mean relative differences distributions. For the same scaling factor and soil texture, simulated shapes of the mean relative differences distributions depended on the duration of the simulation period and the season. Variation in mean relative differences was higher in coarser textures than in finer ones and more variability was seen in the topsoil than in the subsoil. Root water uptake decreased the mean relative differences variability in the root zone and increased variability below it. This work presents a preliminary research to promote the use of water flow simulations under site-specific conditions to better understand the temporal stability of soil water contents. The estimation of the spatial variability of from soil water content monitoring presents an interesting avenue for further research.
    Keywords: Soil Water Content ; Temporal Stability ; Simulations ; Local Controls ; Saturated Hydraulic Conductivity ; Geography
    ISSN: 0022-1694
    E-ISSN: 1879-2707
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  • 7
    Language: English
    In: Soil Science Society of America Journal, March, 2013, Vol.77(2), p.350(12)
    Description: The combination of runoff plot studies and soil tracking using a silt size magnetic sediment tracer, allowed a better understanding of the relative contribution of different zones in olive (Olea europaea L.) orchard plots to total soil losses. The average erosion rates were different in the tree rows (tr) (0.8 kg m-2 mo-1) and in the inter-tree rows (itr) (1.4 kg m-2 mo-1), inter-tree rills (r) being the most eroded areas (4 kg m-2 mo-1) from October 2008 to April 2010. Since soil under the olive canopies has a high infiltration capacity, splash is a major erosion process in this area, while, in the itr, sheet and rill erosion are the dominant processes. The proposed magnetic tracer technology was an effective tool for determining the cumulative soil losses at the plots for a 17 mo period (average 141 Mg ha-1) with an accuracy of 7.2 Mg ha-1. To achieve this accuracy, determination of bulk density, selectiveness in the transport process, tracer distribution in the soil profile and field calibration of the magnetic susceptibility probe were required. The evolution of tracer distribution provided insight into soil displacement within the runoff plots due to erosion processes. The tracer distribution maps also indicate a high coefficient of variability of the incorporation of tagged soil into the plot, which should be improved in future research to increase the usefulness of this approach in water erosion studies.
    Keywords: Olives -- Environmental Aspects ; Orchards -- Environmental Aspects ; Soil Erosion -- Environmental Aspects ; Soil Research
    ISSN: 0361-5995
    Source: Cengage Learning, Inc.
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  • 8
    In: International Agrophysics, 07/1/2016, Vol.30(3), pp.349-357
    Description: Understanding of soil spatial variability is needed to delimit areas for precision agriculture. Electromagnetic induction sensors which measure the soil apparent electrical conductivity reflect soil spatial variability. The objectives of this work were to see if a temporally stable component could be found in electrical conductivity, and to see if temporal stability information acquired from several electrical conductivity surveys could be used to better interpret the results of concurrent surveys of electrical conductivity and soil water content. The experimental work was performed in a commercial rainfed olive grove of 6.7 ha in the ‘La Manga’ catchment in SW Spain. Several soil surveys provided gravimetric soil water content and electrical conductivity data. Soil electrical conductivity values were used to spatially delimit three areas in the grove, based on the first principal component, which represented the time-stable dominant spatial electrical conductivity pattern and explained 86% of the total electrical conductivity variance. Significant differences in clay, stone and soil water contents were detected between the three areas. Relationships between electrical conductivity and soil water content were modelled with an exponential model. Parameters from the model showed a strong effect of the first principal component on the relationship between soil water content and electrical conductivity. Overall temporal stability of electrical conductivity reflects soil properties and manifests itself in spatial patterns of soil water content.
    Keywords: Agriculture;
    ISSN: International Agrophysics
    ISSN: 02368722
    E-ISSN: 2300-8725
    Source: Walter de Gruyter (via CrossRef)
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  • 9
    Language: English
    In: Soil Science Society of America Journal, 2013, Vol.77(2), p.350
    Description: The combination of runoff plot studies and soil tracking using a silt size magnetic sediment tracer, allowed a better understanding of the relative contribution of different zones in olive (Olea europaea L.) orchard plots to total soil losses. The average erosion rates were different in the tree rows (tr) (0.8 kg m super(-2) mo super(-1)) and in the inter-tree rows (itr) (1.4 kg m super(-2) mo super(-1)), inter-tree rills (r) being the most eroded areas (4 kg m super(-2) mo super(-1)) from October 2008 to April 2010. Since soil under the olive canopies has a high infiltration capacity, splash is a major erosion process in this area, while, in the itr, sheet and rill erosion are the dominant processes. The proposed magnetic tracer technology was an effective tool for determining the cumulative soil losses at the plots for a 17 mo period (average 141 Mg ha super(-1)) with an accuracy of 7.2 Mg ha super(-1). To achieve this accuracy, determination of bulk density, selectiveness in the transport process, tracer distribution in the soil profile and field calibration of the magnetic susceptibility probe were required. The evolution of tracer distribution provided insight into soil displacement within the runoff plots due to erosion processes. The tracer distribution maps also indicate a high coefficient of variability of the incorporation of tagged soil into the plot, which should be improved in future research to increase the usefulness of this approach in water erosion studies. [PUBLICATION]
    Keywords: Soil ; Tracers ; Erosion ; Trees ; Soil Profiles ; Infiltration ; Silt ; Transport Processes ; Canopies ; Iron ; Orchards ; Technology ; Olea ; Olea Europaea ; Renewable Resources-Terrestrial;
    ISSN: Soil Science Society of America Journal
    E-ISSN: 0361-5995
    E-ISSN: 14350661
    Source: CrossRef
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  • 10
    In: Soil Science, 2012, Vol.177(6), pp.369-376
    Description: ABSTRACT: Spatial estimation of soil-water content (θ) at the field, hillslope, or catchment scale is required in numerous applications. Time-lapse electrical resistivity and apparent electrical conductivity (ECa) surveys are recognized as a useful source of information about both spatial variations in θ and spatial differences in soil properties. The objective of this work was to test the hypothesis that the accuracy of the regression relationships between θ and collocated ECa survey data can be improved for any given time if several time-lapse ECa surveys rather than a single ECa survey are used. Vertisol plots under conventional tillage and direct drilling were surveyed for gravimetric θ (θg) in the top 0.3-m layer at 17 times and for topsoil ECa at 13 times in 2008 through 2010. Both dry and wet periods were covered by the surveys. On four occasions, θg and ECa surveys were done on the same day. Only weak correlations (with R 〈 0.21) were found between ECa and θg measured on the same day. The accuracy of regression predictions of θg substantially improved when data of several ECa surveys, rather than a single survey, were used. Therefore, the knowledge about the temporal variability in soil properties, as captured by the time-lapse ECa data, can improve the estimation of spatial variability in soil properties affecting soil-water content.
    Keywords: Agriculture;
    ISSN: 0038-075X
    E-ISSN: 15389243
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