• Authors:
    • Carr, M.
  • Source: Experimental Agriculture
  • Volume: 48
  • Issue: 3
  • Year: 2012
  • Summary: The results of research on the water relations and irrigation need of Citrus spp. are collated and reviewed in an attempt to link fundamental studies on crop physiology to drought mitigation and irrigation practices. Background information is given on the centres of origin (south-east Asia) and of production of citrus (areas with subtropical Mediterranean-type climates). The effects of water stress on the development processes of the crop are summarised followed by reviews of the plant water relations, crop water requirements, water productivity and irrigation systems. The topic is complicated by the diversity of species and cultivars (including rootstocks) that are embraced within Citrus spp. The effects of water availability on vegetative growth are understood in general terms, but the relationships have not yet been quantified. Similarly, the need for a 'rest period' to induce flowering is understood, but its magnitude (in terms of a drought stress index or day-degrees) does not appear to have been specified with precision. Again, the effects of drought on flower and fruit formation and retention are understood in general terms, but the relationships have not been quantified in useful ways for specific cultivars. Rooting depth and distribution have only been described in a limited number of situations. Environmental factors influencing stomatal conductances are generally well described and relationships with some growth processes established. Compared with other crops, low stomatal/canopy conductance restricts water use of Citrus spp. Some (limited) progress has been made in quantifying crop water requirements in specific conditions. Despite many recent attempts to specify how little water can be applied at specific growth stages to optimise water productivity through regulated deficit irrigation, no consensus view has emerged. The yield response to 'full' irrigation is of the order 6-7 kg fresh fruit m -3 as a result of an increase in the number of fruit of marketable size. There are also improvements in fruit quality. The most effective way of irrigating a citrus orchard is with a microirrigation system (drip or microsprinklers), but both methods require answers to the question: what proportion of the root zone needs to be irrigated? Both methods, especially drip, allow water to be applied (with fertigation) at very frequent intervals (including several times a day), although formal evidence of the benefits to be obtained from this level of intensification is lacking.
  • Authors:
    • Oliveira, P.
    • Coelho Filho, M.
    • Coelho, E.
  • Source: Acta Horticulturae
  • Issue: 928
  • Year: 2012
  • Summary: Meeting the increased water requirement in agriculture due to the increases of irrigated areas in order to provide food for growing populations, relies on the application of water with increased efficiency. This work evaluated the partial root drying technique for lemon 'Tahiti' trees under semi-arid climate conditions in the north of Minas Gerais. The experiment was carried out in randomized block design with nine treatments and four replicates. Treatments were based on percentages of reduction of calculated irrigation water depth, i.e., 25% corresponding to the reduction of irrigation on one quarter of the area occupied by the plant and 50% corresponding to the reduction of irrigation on half of the plant area during three phonological phases (I, II and III) of lemon 'Tahiti'. The results showed that irrigation scheduling using the partial root drying method may be performed with any of the treatments evaluated. The larger yields and water use efficiencies were obtained for treatments T7 and T8 which were a reduction of 25% of total irrigation every 7 or 15 days during flowering followed by a reduction of 50% of total irrigation every 7 or 15 days in phases II and III.
  • Authors:
    • Olsson, O.
    • Isopi, A.
    • Dimico, A.
  • Source: Credit Research Paper
  • Issue: 12/01
  • Year: 2012
  • Summary: Since its first appearance in the late 1800s, the origins of the Sicilian mafia have remained a largely unresolved mystery. Both institutional and historical explanations have been proposed in the literature through the years. In this paper, we develop an argument for a market structure-hypothesis, contending that mafia arose in towns where firms made unusually high profits due to imperfect competition. We identify the market for citrus fruits as a sector with very high international demand as well as substantial fixed costs that acted as a barrier to entry in many places and secured high profits in others. We argue that the mafia arose out of the need to protect citrus production from predation by thieves. Using the original data from a parliamentary inquiry in 1881-86 on all towns in Sicily, we show that mafia presence is strongly related to the production of orange and lemon. This result contrasts recent work that emphasizes the importance of land reforms and a broadening of property rights as the main reason for the emergence of mafia protection.
  • Authors:
    • Chehbouni, A.
    • Lepag, M.
    • Jarlan, L.
    • Ezzahar, J.
    • Erraji, T.
    • Khabba, S.
    • Er-Raki, S.
    • Hanich, L.
  • Source: Acta Horticulturae
  • Issue: 951
  • Year: 2012
  • Summary: Sap flow measurements based on heat balance method gives a direct measurement of the mass flow rate of sap in the stem. However, extrapolation of these measurements from the stem to the field scale is an important challenge. In this study, 15 branches of citrus trees with different diameters were equipped with Dynamax sap flow gauge. These individual branch measurements have been after extrapolated to the canopy transpiration by using two up-scaling methods. The first one uses the relationship between sap flow and branches diameter and the second one uses the distribution of the branch diameter in the orchards. The results showed a good agreement between the two methods estimates (R 2=0.95). A comparison between scaled-up transpiration from sap flow and measured evapotranspiration (ET ed) by eddy covariance showed an average daily difference of about 0.87 mm/day which represents 25% of ET ed. This substantial amount of water was lost through soil evaporation and part of it could be saved by improving the drip irrigation management.
  • Authors:
    • Frisvold, G. B.
    • Konyar, K.
  • Source: Water Resources Research
  • Volume: 48
  • Issue: 5
  • Year: 2012
  • Summary: This study examined how agriculture in six southwestern states might adapt to large reductions in water supplies, using the U.S. Agricultural Resource Model (USARM), a multiregion, multicommodity agricultural sector model. In the simulation, irrigation water supplies were reduced 25% in five Southern Mountain (SM) states and by 5% in California. USARM results were compared to those from a "rationing" model, which assumes no input substitution or changes in water use intensity, relying on land fallowing as the only means of adapting to water scarcity. The rationing model also ignores changes in output prices. Results quantify the importance of economic adjustment mechanisms and changes in output prices. Under the rationing model, SM irrigators lose $65 in net income. Compared to this price exogenous, "land-fallowing only" response, allowing irrigators to change cropping patterns, practice deficit irrigation, and adjust use of other inputs reduced irrigator costs of water shortages to $22 million. Allowing irrigators to pass on price increases to purchasers reduced income losses further, to $15 million. Higher crop prices from reduced production imposed direct losses of $130 million on first purchasers of crops, which include livestock and dairy producers, and cotton gins. SM agriculture, as a whole, was resilient to the water supply shock, with production of high value specialty crops along the Lower Colorado River little affected. Particular crops were vulnerable however. Cotton production and net returns fell substantially, while reductions in water devoted to alfalfa accounted for 57% of regional water reduction.
  • Authors:
    • Arriaga-Sevilla, J.
    • Durán-Zuazo, V. H.
    • García-Tejero, I.
    • Muriel-Fernández, J. L.
  • Source: Agronomy for Sustainable Development
  • Volume: 32
  • Issue: 3
  • Year: 2012
  • Summary: Water shortage is becoming a severe problem in arid and semi-arid regions worldwide, reducing the availability of agricultural land and water resources. Deficit irrigation strategies can improve water-use efficiency and the sustainability of agro-ecosystems, although it is important to model the effects on yield loss due to irrigation water restrictions. This work estimates the water production function in citrus trees, determining the relationship between plant water stress and yield depression, as well as establishing a mathematical model for each phenological stage considered (flowering, fruit growth and ripening), and for the entire productive process. For three consecutive years (2006-2008), four regulated deficit irrigation treatments plus a control (100% crop water evapotranspiration (ET C)) were implemented in 13-year-old citrus trees ( Citrus sinensis L. Osb. cv. Navelina). Different water production functions were determined for each phenological stage, establishing the relationship between the irrigation water stress and crop yield. Our results show that the fruit growth and flowering stages were the most sensitive periods in relation to irrigation water deficit and yield loss. Water stress close to 50% of ET C during the flowering stage would impose a yield loss of up to 20%, whereas this same water stress level during the fruit growth or ripening stages would result in yield losses of nearly 10% and 6%, respectively. The adjustment with cross terms ( r2=0.87) estimated the yield loss with good accuracy, being very similar to data measured in each study season. Consequently, the combined effect of deficit irrigation in different stages would be an additive-multiplicative model, considering that the effect of water stress in previous periods determined the crop yield response. Our model indicated that the crop water production function under deficit irrigation programmes would have a quasi-linear relation for water deficits below to 40% ET C. The previous model functions did not enable us to establish an accurate relationship when the water stress was applied in different phenological stages. Thus, this new interpretation is valuable to improve our knowledge and predict the impact of regulated deficit irrigation and have potential application in precision water stress and sustainable irrigation scheduling for citrus.
  • Authors:
    • Arriaga, J.
    • Muriel-Fernández, J. L.
    • Durán-Zuazo, V. H.
    • García-Tejero, I. F.
  • Source: Scientia Horticulturae
  • Volume: 133
  • Year: 2012
  • Summary: This study examines the suitability of trunk dendrometers for assessing fruit growth under deficit irrigation (DI) for two consecutive years in a mature citrus orchard. Two DI programmes were applied during the maximum evapotranspirative demand period: sustained-deficit irrigation, applied at 50% ET C on average, and low-frequency deficit irrigation, applied according to plant-water status, establishing different irrigation-restriction cycles. Additionally, a control treatment at 100% ET C was monitored for the entire irrigation season. Trunk daily growth (TDG) and fruit daily growth (FDG) were estimated together with stem-water potential at midday (Psi stem) and the maximum daily shrinkage of the trunk (MDS). Significant relationships were determined for Psi stem vs. TDG ( R2=0.60), and vs. FDG ( R2=0.78). In addition, significant relationships were established between TDG vs. FDG ( R2=0.60), and between the daily increment of MDS (DeltaMDS) and FDG ( R2=0.50), revealing the strong connection between trunk and fruit variations caused by water stress. According to these findings, the DI effects on fruit growth can be monitored by means of TDF or temporal evolution of Psi stem, promising automation possibilities for appropriately regulating irrigation under DI programmes, and predicting its effects on fruit size by continuous field measurement.
  • Authors:
    • Lopes, S. A.
    • Bassanezi, R. B.
    • Gasparoto, M. C. G.
    • Coletta-Filho, H. D.
    • Amorim, L.
    • Lourenço, S. A.
  • Source: Plant Pathology
  • Volume: 61
  • Issue: 4
  • Year: 2012
  • Summary: The objectives of this work were (i) to determine the influence of temperature on infection of citrus by 'Candidatus Liberibacter asiaticus' and 'Candidatus Liberibacter americanus', the two bacterial species associated with citrus huanglongbing (HLB) in Brazil, and (ii) to determine the influence of temperature on citrus colonization by 'Ca. L. asiaticus', which has taken over from 'Ca. L. americanus' as the predominant species in Brazil since 2008. Two experiments were carried out with graft-inoculated Valencia oranges on Rangpur lime rootstocks. Immediately after inoculation the plants were maintained for 423 days in growth chambers under the following night/day temperature conditions: 17/22, 22/27 or 27/32°C, with a dark/light photoperiod of 8/16 h. Infection and colonization of plants were determined using quantitative PCR (qPCR). ' Candidatus Liberibacter americanus' did not infect the plants maintained at 27/32°C; however, infection by 'Ca. L. asiaticus' occurred at all studied temperatures. Two months after inoculation, 'Ca. L. asiaticus' was distributed throughout the inoculated plants, with mean Ct values in the range of 30-31 for leaves and 25-28 for roots. Over time, ' Ca. L. asiaticus' reached the highest titres in mature leaves (mean Ct value=26.7) of citrus plants maintained at 22/27°C. 'Candidatus Liberibacter asiaticus' colonization of citrus plants was negatively affected by the daily temperature regime of 27/32°C (mean Ct value in mature leaves=33.6).
  • Authors:
    • Hau, B.
    • Lourenco, S. A.
    • Stuchi, E. S.
    • Goncalves, F. P.
    • Amorim, L.
  • Source: Plant Pathology
  • Volume: 91
  • Issue: 11
  • Year: 2012
  • Summary: Citrus Variegated Chlorosis (CVC) is currently present in approximately 40% of citrus plants in Brazil and causes an annual loss of around 120 million US dollars to the Brazilian citrus industry. Despite the fact that CVC has been present in Brazil for over 20 years, a relationship between disease intensity and yield loss has not been established. In order to achieve this, an experiment was carried out in a randomized block design in a 3*2 factorial scheme with 10-year-old Natal sweet orange. The following treatments were applied: irrigation with 0, 50 or 100% of the evapotranspiration of the crop, combined with natural infection or artificial inoculation with Xylella fastidiosa, the causal agent of CVC. The experiment was evaluated during three seasons. A negative exponential model was fitted to the relationships between yield versus CVC severity and yield versus Area Under Disease Progress Curve (AUDPC). In addition, the relationship between yield versus CVC severity and canopy volume was fitted by a multivariate exponential model. The use of the AUDPC variable showed practical limitations when compared with the variable CVC severity. The parameter values in the relationship of yield-CVC severity were similar for all treatments unlike in the multivariate model. Consequently, the yield-CVC intensity relationship (with 432 data points) could be described by one single model: y=114.07 exp(-0.017 x), where y is yield (symptomless fruit weight in kg) and x is disease severity ( R2=0.45; P
  • Authors:
    • Silva, J. A. A.
    • Modesto, R. T.
    • Miguel, F. B.
    • Grizotto, R. K.
    • Vieira Jr., J. B.
  • Source: Revista Brasileira de Engenharia Agrícola e Ambiental
  • Volume: 16
  • Issue: 7
  • Year: 2012
  • Summary: The effect of a technological package implemented in a Valencia orange orchard was studied and compared with the conventional system, based on the production and quality of the fruits harvested. The technologies implemented included the densification, fertilization during implantation and training, phytosanitary treatment, weed management, irrigation and pruning. The results for the fruits from the first harvest showed that the Technified System and Irrigation (TS+I) resulted in significant increase in crop yield. This increase was higher in orchards with a higher density of 727 plants ha -1 (5.5*2.5 m spacing) or 667 plants ha -1 (6.0*2.5 m spacing). In general, irrigation concomitant with TS resulted in larger sized fruits and consequently less fruit per standard sized box, and lower soluble solids and titrable acidity. There was no effect on juice yield with the production system or spacing. It is concluded that, in this first evaluation, orchard management technologies concomitant with irrigation (TS+I) is interesting because promoted an increase in crop yield compared to conventional systems.