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Acalá del Río, Spain

Perez-Guerrero S.,Centro Las Torres Tomejil | Gelan-Begna A.,University of Cordoba, Spain | Vargas-Osuna E.,University of Cordoba, Spain
BioControl | Year: 2015

Intraguild predation (IGP) among predatory arthropods can impair pest control efforts and endanger the joint-action compatibility of groups of natural enemies. The present study used plant microcosms to examine IGP of Cheiracanthium pelasgicum (C. L. Koch) (Araneae: Miturgidae) on minute pirate bugs Orius laevigatus (Fieber) (Hemiptera: Anthocoridae), two of the major lepidopteran-egg predators in southern Spanish cotton fields, and its effects on the control of Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) eggs. Intensive unidirectional IGP of C. pelasgicum on O. laevigatus was observed under plant arena conditions: over 90 % of minute bugs were killed by spiders in the first 24 h. However, no negative interaction between C. pelasgicum and minute pirate bugs was found under different egg-density conditions with Orius alone, and the combination of two predator treatments displayed significantly higher predation rates than the spider-alone treatment after 24 h. Increased egg density did not affect control by predators, nor did it prompt a significant reduction in IGP. During a day–night bioassay, negative interaction between the two predators was found under night conditions, impacting on egg predation rates due to the combination of two predators. Predation of spiders on H. armigera eggs took place mainly at night, while predation by minute bugs was recorded both by day and by night. Finally, IGP by C. pelasgicum on minute pirate bugs was significantly higher by night. These outcomes demonstrate that diurnal and more intensive nocturnal IGP by spiders on minute pirate bugs had a moderate impact on the early control of H. armigera, with no negative effects after 24 h. © 2015 International Organization for Biological Control (IOBC) Source

Green S.R.,Plant and Food Research | Romero R.,Centro Las Torres Tomejil
Acta Horticulturae | Year: 2012

Thermal methods, including heat-pulse, have been used to measure sap flow for many decades. In most cases, analysis and interpretation of the temperature signals has remained largely unchanged since the pioneering work of Marshall (1958) and the theoretical calibrations of Swanson and Whitfield (1983). Two recent advances to heat-pulse have been developed to improve measurements at low flows; the 'Average Gradient' method (CAG) of Villalobos and Testi (2008), which modified the 'compensation method' (CHP) to improve sensitivity at low flows (i.e. < 10 cm h-1), and the 'Heat Ratio Method' (HRM) of Burgess et al. (2001) which employs temperature ratios measured at equal distances either side of the heater source. Preliminary results from CHP, CAG and HRM are compared against lysimeter data from potted trees to demonstrate the performance of these methods across a range of flows. We also propose and test two new methods to resolve low sap flow. The first method we will call the Symmetrical Gradient method (SGM). It consists of averaging the temperature-difference signal (δT) of two probes that are equidistant from the heater. The second method we will call the Maximum Derivative Method (MDM). The analysis of MDM is based on the maximum rate of change of the temperature difference curve (i.e. the derivative, δT'max). We have applied this derivative approach to temperature data collected using both symmetrical and assymetrical probe arrangements. Our measurements suggest these two indicators (δT and δT'max) are proportional to the sap flow across a wide range of flows. Data suggests our new 'calibrated maximum derivative' CMD method (CMD), is a simple and practical means to extend CHP over the low-flow regime. Source

Duran Zuazo V.H.,Centro Las Torres Tomejil | Rodriguez Pleguezuelo C.R.,Centro Camino Of Purchil | Francia Martinez J.,Centro Camino Of Purchil | Martin Peinado F.J.,University of Granada
Journal of Land Use Science | Year: 2013

Resource use and watershed management have become an increasingly important issue, stressing the need to find appropriate management approaches for improving agricultural landscapes. We analysed land-use changes from 1978 to 2007 in a representative watershed of Almuñécar (SE Spain). In 1978 the watershed consisted of 64.2% almond, 24.7% fallow land, 6.7% vineyard, 1.9% olive and 2.5% other uses. In 2007 much of the traditional orchards had disappeared, leaving only 17% almond and 0.6% vineyard. Not less than 29.8% had become shrubland and another 24.6% abandoned cropland. However, much of the land is now under subtropical crops: 19.2% avocado (Persea americana M.), 3.9% mango (Mangifera indica L.), 2.4% loquat (Eriobotrya japonica L.) and 1.1% cherimoya (Annona cherimola M.). This intensively irrigated agriculture with subtropical trees on terraces could exacerbate watershed degradation and could become a core problem with implications for sustainable resource use. The abandonment of traditional terraces with rainfed crops has led to the re-emergence of spontaneous native vegetation, promoting a denser plant cover and subsequent decrease in erosion. Therefore, highlighting the need for implementing sustainable conservation practices is crucial as part of future agricultural support. © 2013 Copyright Taylor and Francis Group, LLC. Source

Martinez G.,University of Cordoba, Spain | Martinez G.,U.S. Department of Agriculture | Pachepsky Y.A.,U.S. Department of Agriculture | Vereecken H.,Julich Research Center | And 3 more authors.
Journal of Hydrology | Year: 2013

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 Ksat. 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 Ksat 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 Ksat 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 Ksat from soil water content monitoring presents an interesting avenue for further research. © 2012. Source

Vanderlinden K.,Centro Las Torres Tomejil | Vanderlinden K.,U.S. Department of Agriculture | Vereecken H.,Julich Research Center | Hardelauf H.,Julich Research Center | And 5 more authors.
Vadose Zone Journal | Year: 2012

Temporal stability (TS) of soil water content (SWC) has been observed throughout a wide range of spatial and temporal scales. Yet, the evidence with respect to the controlling factors on TS SWC remains contradictory or nonexistent. The objective of this work was to develop the first comprehensive review of methodologies to evaluate TS SWC and to present and analyze an inventory of published data. Statistical analysis of mean relative difference (MRD) data and associated standard deviations (SDRD) from 157 graphs in 37 publications showed a trend for the standard deviation of MRD (SDMRD) to increase with scale, as expected. The MRD followed generally the Gaussian distribution with R2 ranging from 0.841 to 0.998. No relationship between SDMRD and R2 was observed. The smallest R2 values were mostly found for negatively skewed and platykurtic MRD distributions. A new statistical model for temporally stable SWC fields was proposed. The analysis of the published data on seven measurement-, terrain-, and climate-related potentially control- ling factors of TS SWC suggested intertwined effects of controlling factors rather than single dominant factors. This calls for a focused research effort on the interactions and effects of measurement design, topography, soil, vegetation and climate on TS SWC. Research ave- nues are proposed which will lead to a betier understanding of the TS phenomenon and ultimately to the identification of the underlying mechanisms. © Soil Science Society of America. Source

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