• Authors:
    • Intrigliolo, D.
    • Yeves, A.
    • Sanz, F.
    • Castel, J.
    • Ballester, C.
    • Castel, J.
  • Source: Acta Horticulturae
  • Issue: 922
  • Year: 2011
  • Summary: In citrus trees, regulated deficit irrigation (RDI) can be a useful irrigation strategy to reduce water supply without affecting yield. Previous studies conducted in this sense have determined irrigation water savings achieved by RDI but less is known about the actual transpiration values of the RDI trees. This information is crucial to properly carry out a water balance of an RDI orchard. In an experiment performed during 2009 on mature 'Clementina de Nules' citrus, we determined sap flow (SF) of well irrigated and RDI trees by means of the compensation heat pulse method. SF was measured in two trees per treatment instrumented with one unit of two different gauge types per tree, determining heat velocity at four different xylem depths. SF values obtained at 30-min intervals during the entire experimental period were compared with whole canopy gas exchange measurements carried out during two representative days with custom designed Mylar plastic chambers. Plant water status was determined by midday stem water potential measurements (Psi stem). Results showed that absolute SF values clearly underestimated tree water use. After calibrating SF against canopy gas exchange determinations, corrected SF values appeared more reasonable but it also increased tree-to-tree variability (CV from 0.08 to 0.17). The transpiration ratio (SF RDI/SF control) had a somewhat decreasing trend during the water restriction period according to Psi stem, but recovering before the irrigation was resumed to normal dose. Overall, the results highlight some of the problems and uncertainties when using a limited number of sap flow sensors for detecting plant water stress and for accurately measuring transpiration.
  • Authors:
    • Muriel-Fernández, J. L.
    • Jiménez-Bocanegra, J. A.
    • Durán-Zuazo, V. H.
    • Romero, R.
    • García-Tejero, I.
  • Source: Acta Horticulturae
  • Issue: 922
  • Year: 2011
  • Summary: Three different deficit-irrigation strategies were studied: sustained deficit irrigation (SDI), regulated deficit irrigation (RDI), and low-frequency deficit irrigation (LFDI) in different commercial citrus orchards located in the Guadalquivir river basin SW Spain. Each irrigation treatment was based on different water-stress ratio (WSR), which is the ratio of water supplied to deficit-irrigation treatment with respect to the control treatment (100% ET C). Midday stem-water potential (Psi Stem) was measured during the irrigation periods and was used to characterize plant-water status. Also, integrated stem-water potential (Psi Int) was calculated for all treatments and used as a timing water-stress indicator for the crop. Yield and fruit quality were evaluated at harvest in each treatment taking into account the temporal and spatial variability, associated mainly with local weather conditions, and agronomic orchard management. Relationships among water applied, Psi Int and yield response were performed to quantify the effects of deficit irrigation on yield and fruit-quality parameters. Analysis of data showed that, in all cases, the irrigation-water restriction significantly affected yield and some fruit-quality parameters (total soluble solids, titratable acidity, and maturity index). The results confirmed that the water productivity (WP) was positively related to water amount and irrigation strategy applied. Consequently, when WSR of 0.70 was applied (moderate deficit irrigation) RDI strategy showed better results than the SDI. However, with WSR of 0.60 (severe water reduction), LFDI strategy provided the best crop response. Under Mediterranean climate and water scarcity conditions, the application of DI strategies allowed water savings up to 1000 m 3 ha -1 yr -1. In DI treatments, the total water applied was better correlated with WP than with yield, indicating that this parameter should be used when trying to improve irrigation management.
  • Authors:
    • Muriel-Fernandez, J. L.
    • Duran-Zuazo, V. H.
    • Garcia-Tejero, I.
  • Source: Comunicata Scientiae
  • Volume: 2
  • Issue: 2
  • Year: 2011
  • Summary: Long-term impact of different sustained-deficit irrigation (SDI) treatments on a 13-year-old orange orchard ( Citrus sinensis L. Osbeck, cv. Salustiana) was studied from 2004 to 2008. The experiment consisted of a control irrigation treatment which was applied at 100% of the crop evapotranspiration (ETc) values for the whole season, and three SDIs imposed as a function of different water-stress index (WSI) values, defined as the ratio of the actual volume of water supply to the ETc rate. The values defined by the WSI were 0.75, 0.65, and 0.50. The plant-water status was measured through the midday stem-water potential (Psi Stem). Yearly, yield and fruit quality were evaluated at harvest in each treatment, and a global analysis was carried out using the whole dataset. Overall, no significant differences were found in fruit yield between SDIs and control treatments, although significant differences appeared in some of the fruit-quality parameters (total soluble solids and titrable acidity) which also showed significant relationships with integrated stem-water potential (Psi Int) and irrigation water applied. These findings lead us to conclude that SDIs have important and statistically significant effects on fruit quality. Thus, the application of sustained-deficit irrigation (SDI with WSI of 50) provides promising possibilities for optimising citrus irrigation and boosting the water productivity for citrus orchards in a semiarid Mediterranean climate.
  • Authors:
    • Muriel-Fernández, J. L.
    • Durán-Zuazo, V. H.
    • García-Tejero, I.
    • Martínez-García, G.
    • Jiménez-Bocanegra, J. A.
  • Source: Agronomy for Sustainable Development
  • Volume: 31
  • Issue: 4
  • Year: 2011
  • Summary: Citrus is a crop of major economic importance in Spain, cultivated during the dry season when irrigation is essential to guarantee yields of high quality. As water resources are progressively more insufficient, more effective water management in agriculture is crucial. Deficit irrigation in many agricultural crops has frequently proved to be an efficient tool for improving water-use efficiency. We hypothesise that, despite the effectiveness of deficit irrigation, the most suitable strategy in citrus orchards remains to be defined for Mediterranean environment. In this study, for the period from 2006 to 2008, a 12-year-old orange orchard, Citrus sinensis L. Osb. cv. Navelina, grafted onto Carrizo citrange, C. sinensis L. Osb. * Poncirus trifoliata L. Osb., were subjected under two deficit-irrigation strategies defined as follows: (1) low-frequency deficit irrigation applied according to the plant-water status, and (2) sustained-deficit irrigation with a water-stress ratio of 0.6, defined as the ratio of actual water-limited supply in this treatment related to the water supply of the control treatment. The control treatment was irrigated at 100% of ET C for the entire irrigation season (ET C: crop evapotranspiration). Midday stem-water potential (Psi stem) and stomatal conductance ( gS) were used to estimate the water status of the trees. The lowest Psi stem and g S values were registered in the deficit-irrigation treatments with a seasonal pattern consistent with the irrigation dynamics applied in each case. Psi stem and gS values significantly differed from those of the control trees. Although the integrated stress levels were similar in deficit-irrigation treatments, differences in yield and fruit quality were found, having a more positive response to low-frequency deficit irrigation with an increase of 25% in yield in comparison to the sustained-deficit irrigation treatment. Here, we thus demonstrate the significant differences in water productivity. Indeed, water productivity parameter not only depends on the amount of water, but also on the irrigation strategy applied, which promoted substantial water savings without significant impact on yield. The present study highlights that low-frequency deficit irrigation should be adopted as a most appropriate strategy for achieving sustainable water management and attains reasonable yields and improves quality in citrus orchards under Mediterranean semiarid climate.
  • Authors:
    • Muriel-Fernández, J. L.
    • Durán-Zuazo, V. H.
    • García-Tejero, I. F.
    • Jiménez-Bocanegra, J. A.
  • Source: Functional Plant Biology
  • Volume: 38
  • Issue: 2
  • Year: 2011
  • Summary: The continuous monitoring of crop water status is key to the sustainable management of water stress situations. Two deficit irrigation (DI) treatments were studied during the maximum evapotranspirative demand period in an orange orchard ( Citrus sinensis (L.) Osb. cv. Navelina): sustained deficit irrigation irrigated at 55% crop evapotranspiration (ET C), and low-frequency deficit irrigation treatment, in which the plants were irrigated according to stem water potential at midday (Psi stem). Additionally, a control treatment irrigated at 100% of ET C was established. The daily canopy temperature ( TC) was measured with an infrared thermometer camera together with measurements of trunk diameter fluctuations (TDF), Psi stem and stomatal conductance ( gS). The time course of all physiological parameters and their relationships were analysed, confirming that canopy air temperature differential ( TC- Ta) variations and TDF are suitable approaches for determining the water stress. In addition, the maximum daily shrinkage (MDS) and TC- Ta showed high sensitivity to water stress in comparison to Psi stem and gS. Significant relationships were found among MDS and TC- Ta with Psi stem and gS, for monitoring the crop water status by means of MDS vs Psi stem and TC- Ta vs Psi stem. Thus, the combination of these techniques would be useful for making scheduling decisions on irrigation in orchards with high variability in plant water stress.
  • Authors:
    • Gutierrez-Martin, C.
    • Gomez Gomez, C. M.
  • Source: Spanish Journal of Agricultural Research
  • Volume: 9
  • Issue: 4
  • Year: 2011
  • Summary: This paper develops a general preference model to explain farmers' decisions. Contrary to better known and most commonly used simulation models, the one presented in this paper allows to calibrate, simulate and explain farmers' decisions without assuming linear preferences (as in many multi criteria decision models) or unobservable implicit cost functions (as in positive mathematical programming models). The model is calibrated for crop decisions in the Genii Cabra irrigated area in the Guadalquivir valley (South Spain) as the resulting empirical model is used to study how farmers react by adjusting these decisions when efficiency in the use of water is improved under different scenarios regarding water use rights. The main conclusion of the paper is that the potential water savings from enhancing irrigation technique (636 m(3) ha(-1)) are overcome by increasing water demand due to higher per drop water productivity when sunflower is replaced by maize. For that reason water price increases and/or reduction of water use rights is a necessary condition to convert water savings through improved efficiency into lower water use and better conserved water sources.
  • Authors:
    • Navarrete, L.
    • Kozak, M.
    • Hernandez Plaza, E.
    • Gonzalez-Andujar, J. L.
  • Source: Agriculture, Ecosystems and Environment
  • Volume: 140
  • Issue: 1-2
  • Year: 2011
  • Summary: This study investigated whether the choice of a tillage system (no-tillage, minimum tillage or traditional tillage) affected weed diversity in a 23 years cereal-leguminous rotation system in Spain. Weed diversity was assessed using common diversity indices: species richness, Shannon's index and Pielouis evenness. Linear mixed-effects models were employed to compare the tillage systems. It was found that after 23 years no large differences between tillage systems have arisen related to weed diversity. Only minimum tillage appeared to support, on average, more species than the two other tillage systems. Richness, Shannon diversity index and evenness varied largely through the years in all tillage systems but this variation was not related to type of crop sown (cereal or leguminous). Our results highlight that conservation tillage practices did not represent any concern for weed diversity conservation in cereal-leguminous rotations in the conditions of central Spain.
  • Authors:
    • Castel, J. R.
    • Ballester, C.
    • Jiménez-Bello, M. A.
    • Intrigliolo, D. S.
  • Source: Agricultural Water Management
  • Volume: 98
  • Issue: 10
  • Year: 2011
  • Summary: Leaf temperature is a physiological trait that can be used for monitoring plant water status. Nowadays, by means of thermography, canopy temperature can be remotely determined. In this sense, it is crucial to automatically process the images. In the present work, a methodology for the automatic analysis of frontal images taken on individual trees was developed. The procedure can be used when cameras take at the same time thermal and visible scenes, so it is not necessary to reference the images. In this way, during the processing in batch, no operator participated. The procedure was developed by means of a non supervised classification of the visible image from which the presence of sky and soil could be detected. In case of existence, a mask was performed for the extraction of intermediate pixels to calculate canopy temperature by means of the thermal image. At the same time, sunlit and shady leaves could be detected and isolated. Thus, the procedure allowed to separately determine canopy temperature either of the more exposed part of the canopy or of the shaded portion. The methodology developed was validated using images taken in several regulated deficit irrigation trials in Persimmon and two citrus cultivars (Clementina de Nules and Navel Lane-Late). Overall, results indicated that similar canopy temperatures were calculated either by means of the automatic process or the manual procedure. The procedure developed allows to drastically reduce the time needed for image analysis also considering that no operator participation was required. This tool will facilitate further investigations in course for assessing the feasibility of thermography for detecting plant water status in woody perennial crops with discontinuous canopies. Preliminary results reported indicate that the type of crop evaluated has an important influence in the results obtained from thermographic imagery. Thus, in Persimmon trees there were good correlations between canopy temperature and plant water status while, in Clementina de Nules and Navel Lane-Late citrus cultivars canopy temperature differences among trees could not be related with tree-to-tree variations in plant water status.
  • Authors:
    • Armengot, L.
    • Blanco-Moreno, J. M.
    • Jose-Maria, L.
    • Xavier Sans, F.
  • Source: Agriculture, Ecosystems & Environment
  • Volume: 145
  • Issue: 1
  • Year: 2011
  • Summary: Agricultural intensification, at local and landscape scales, has caused a decrease in plant diversity and changes in species composition in cereal fields. To better understand the role of landscape complexity and farming systems in shaping plant assemblages, it is of interest to focus on functional traits rather than on floristic composition, which may help to highlight trends in vegetation patterns. We analysed the relative abundance of various functional attributes (different life forms, growth forms, wind-pollinated species and wind-dispersed species) at three contrasted field positions (boundary, edge and centre) of 29 organic and 29 conventional cereal fields distributed in 15 agrarian localities of NE Spain. Agricultural intensification affected the biological attributes of the vegetation in dryland Mediterranean cereal fields; local factors (farming system and position) had a more prominent role in affecting plant functional composition than the surrounding landscape. Local factors were important for life form distribution, growth form and pollination type, whereas landscape complexity mainly affected the proportion of wind-dispersed species. Therefore, depending on the objective of the study, it is important to select functional attributes sensitive to the different scales of agricultural intensification, especially because landscape complexity and land-use intensity are commonly related.
  • Authors:
    • José-María, L.
    • Sans, F. X.
  • Source: Weed Research
  • Volume: 51
  • Issue: 6
  • Year: 2011
  • Summary: Weed seedbanks are a reserve of weed diversity and can contribute to the prediction of future weed problems in arable fields. Managing seedbanks should therefore help in optimising biodiversity and controlling weed infestations. This study assessed the effects of management system (organic vs. conventional) and landscape complexity on seedbank size and species richness at the edges and centres of Mediterranean dryland cereal fields and examines the relationship between specific management practices and seedbanks. Field edges and organic fields had more species-rich, denser seedbanks than field centres and conventional fields, and landscape complexity had a limited effect on arable seedbanks. Accordingly, the promotion of low-intensity farming practices regardless of landscape complexity, especially at field edges, would be an effective measure for conservation purposes in Mediterranean agroecosystems. Nevertheless, the high seed density of organic seedbanks reveals the need for more effective seedbank management. The analysis of the effects of specific management practices highlights the importance of cleaning crop seeds properly to reduce seedbank size and using complex rotations, especially as this tends to conserve species richness while reducing seed abundance.