• Authors:
    • Moore, A.
    • Ren, H.
    • Alva, A.
  • Source: American Journal of Plant Sciences
  • Volume: 3
  • Issue: 1
  • Year: 2012
  • Summary: Biomass accumulation and partitioning into different plant parts is a dynamic process during the plant growing period, which is influenced by crop management and climate factors. Adequate knowledge of biomass partitioning is important to manage the crops to gain maximum partitioning of assimilates into plant parts of economic significance, i.e. tubers in potato. This study was conducted using two potato cultivars grown in a sandy soil with center pivot irrigation under full irrigation (FI; irrigation to replenish 100% of water loss by evapotranspiration [ET]) and deficit irrigation (DI; replenish only 80% ET) and two nitrogen(N) rates (pre-plant + in-seasonN rates of 56+112 or 168+336 kg/ha). Plant samples were taken on 22, 44, 66, and 98 days after seedling emergence (DAE). With high N rate, tuber biomass of 'Umatilla Russet' cultivar in relation to total plant biomass varied from 23%-88% and 25%-86% over 22 to 98 DAE for the FIand DI treatments, respectively. The corresponding partitioning ranges were 30%-93% and 38%-93% at the low N rate. With respect to the'Ranger Russet' cultivar, biomass partitioning to tubers ranged from 36%-82% and 23%-84% for the FIand DI, respectively, at the high N rate, and 29%-87% and 39%-95% at the low N rate. Overall, this study demonstrated that within the range of N rate and irrigation treatments the biomass portioning into tubers was largely similar in both cultivars.
  • Authors:
    • Intrigliolo, D.
    • Castel, J.
    • Ballester, C.
    • Castel, J.
    • Testi, L.
  • Source: Acta Horticulturae
  • Issue: 951
  • Year: 2012
  • Summary: Transpiration of well watered (C) and regulated deficit irrigated (RDI) trees was determined by means of the compensation heat pulse method during 2009 and 2010 in commercial citrus groves of 'Clementina de Nules' (CN) and 'Navel Lane Late' (NLL). In both species, sap flow (SF) was measured in two trees per treatment instrumented with two gauges per tree. CN trees were equipped with two different types of gauges (type1 shorter than type2) determining heat velocity from crossing time at four different xylem depths according to Green et al. (2003). In NLL oranges, all the gauges were identical and the data were processed according to the compensation heat pulse+calibrated average gradient (CAG) method (Testi and Villalobos, 2009). Plant water status was determined by midday stem water potential measurements (Psistem). Results showed that the absolute SF values, and especially those from type2 gauges in CN, clearly underestimated tree water use. Tree to tree variability registered in CN (CV=0.09) was lower than in NLL (CV=0.17) which also showed a 17% of within tree variability. The average nocturnal-to-diurnal sap flow ratio was between 7% and 13%. The evolution of relative SF (e.g. SF RDI/SF C) was in agreement with differences in Psistem (r 2=0.78 in CN and 0.84 in NLL). This SF ratio showed the expected decreasing trend during the water restriction period and the recovery when irrigation was reestablished to normal dose. Overall, the results show that sap flow sensors can detect plant water stress but they also highlight some of the problems for accurately measuring transpiration.
  • Authors:
    • Aragues, R.
    • Isidoro, D.
    • Barros, R.
  • Source: Agriculture, Ecosystems & Environment
  • Volume: 155
  • Year: 2012
  • Summary: Nitrogen (N) pollution induced by irrigated agriculture is a significant environmental problem. The main N inputs and outputs were measured or estimated in the semi-arid La Violada irrigation district (Spain). Data on two periods (1995-1998 and 2006-2008) were compared and related to observed changes during the decade in cropping patterns and N fertilization and irrigation management. N fertilization exceeded crop N uptake due to over-fertilization of corn (426 kg N/ha in 1995-1998 and 332 kg N/ha in 2006-2008) and alfalfa (62 kg N/ha). Between the two periods, N fertilization decreased by 56%, primarily due to a change from corn to alfalfa and barley. Accordingly, N losses in the irrigation return flows (IRF) diminished from 31% of the applied fertilizer in 1995-1998 to 20% in 2006-2008. NO 3- concentrations and NO 3-N loads in the IRF decreased from 40 mg/L and 106 kg N/ha in 1995-1998 to 21 mg/L and 22 kg N/ha in 2006-2008, due to lower N fertilization, lower corn area and improved irrigation efficiency. N contamination in the IRF will be minimized by increasing the irrigation efficiency and decreasing the corn area and its N fertilization rates, particularly when supplemental organic N is applied at pre-sowing.
  • Authors:
    • Wery, J.
    • Blanco, M.
    • Belhouchette, H.
    • Flichman, G.
  • Source: Computers and Electronics in Agriculture
  • Volume: 86
  • Year: 2012
  • Summary: The aim of this study was to evaluate the sustainability of farm irrigation systems in the Cebalat district in northern Tunisia. It addressed the challenging topic of sustainable agriculture through a bio-economic approach linking a biophysical model to an economic optimisation model. A crop growth simulation model (CropSyst) was used to build a database to determine the relationships between agricultural practices, crop yields and environmental effects (salt accumulation in soil and leaching of nitrates) in a context of high climatic variability. The database was then fed into a recursive stochastic model set for a 10-year plan that allowed analysing the effects of cropping patterns on farm income, salt accumulation and nitrate leaching. We assumed that the long-term sustainability of soil productivity might be in conflict with farm profitability in the short-term. Assuming a discount rate of 10% (for the base scenario), the model closely reproduced the current system and allowed to predict the degradation of soil quality due to long-term salt accumulation. The results showed that there was more accumulation of salt in the soil for the base scenario than for the alternative scenario (discount rate of 0%). This result was induced by applying a higher quantity of water per hectare for the alternative as compared to a base scenario. The results also showed that nitrogen leaching is very low for the two discount rates and all climate scenarios. In conclusion, the results show that the difference in farm income between the alternative and base scenarios increases over time to attain 45% after 10 years.
  • Authors:
    • Villalobos, F.
    • Gomez-Macpherson, H.
    • Boulal, H.
  • Source: Field Crops Research
  • Volume: 130
  • Year: 2012
  • Summary: In the Mediterranean region, conservation agriculture principles like minimum soil disturbance or retaining residues on soil surface are rarely applied in irrigated annual cropping systems. This paper compares a conservation agriculture practice, permanent bed planting (PB), with a conventional system in which the ridges are reformed annually (CB). Comparisons were made throughout a crop sequence of cotton (Gossypium hirsutum L)-maize (Zea mays L) - cotton in which PB was introduced before the maize cropping. Traffic was controlled during the study. Both maize and cotton crops produced higher leaf area index and biomass under PB than CB and Sand 24% higher yield respectively though the yield benefit for maize was not significant. The PB system did not improve Water-use Efficiency but delayed water use until the later growth stages. Soil organic matter (SUM) was significantly higher in PB compared to CB one year after the introduction of the system, and this difference was due to higher SUM in the 0-0.05 m layer, particularly in the furrows. The lack of negative effects of PB on yield and the positive effects on SUM, coupled with increased water infiltration and reduced erosion shown in previous studies, point to the beneficial adoption of PB in the region assuming the patterns are confirmed in the longer term. (C) 2012 Elsevier B.V. All rights reserved.
  • Authors:
    • Jimenez-Martinez, J.
    • Elorza, F.
    • Candela, L.
    • Igel, W.
  • Source: Computers and Electronics in Agriculture
  • Volume: 86
  • Year: 2012
  • Summary: According to the general circulation models (CGMs) for future climate projections, a temperature increase, precipitation decrease, and an increase in the variability of extreme events may be expected in the future, likely reducing available water resources. For the western Mediterranean, future climate change projections indicate that temperature increase may range from 1.5°C to 3.6°C, and the precipitation decline will reach between 10% and 20%, which may result in a significant reduction of natural groundwater recharge. With the use of modelling tools, the amount of groundwater recharge under different climate change scenarios and varying agricultural management practices can be predicted, and water budget attributes can be estimated, which may allow for quantifying impacts, and assist in defining adaptation strategies. For the Inca-Sa Pobla basin (Balearic Islands, Spain), under future climate change projections, agricultural management alternatives of crop type distribution and irrigation demands are required for planned adaptation strategies. In the area, where irrigation water for agricultural practices originates from groundwater resources, adaptation measures based on a change from mixed crops to potatoes and a 20% decrease of agricultural land cultivation have proven to be efficient for the hydrologic system and associated wetland sustainability.
  • 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:
    • Williams, J.
    • Cetin, M.
    • Ibrikci, H.
    • Lounis, A.
    • Hartani, T.
    • Isidoro, D.
    • Topcu, S.
    • Sellam, F.
    • Barros, R.
    • Cavero, J.
    • Araguees, R.
  • Source: Agricultural Water Management
  • Volume: 103
  • Year: 2012
  • Summary: One of the main constraints of irrigated agriculture is off-site N pollution due to export of nitrate in irrigation return flows (IRF). Models capable of simulating the growth of crops and the N loads in IRF as affected by irrigation and N fertilization may be valuable tools in watershed studies. The Agricultural Policy Environmental eXtender (APEX) model was used to assess best management practices for reducing off-site N loads in the IRF of three Mediterranean irrigated watersheds (Akarsu in Turkey, La Violada in Spain and Sidi Rached in Algeria). The watersheds (ranging from 4013 to 10,971 ha) were monitored along three hydrological years to determine the volume of IRF and the NO3-N concentrations and loads in IRF. APEX was calibrated with the data of the first two years and validated with the last year's data. APEX adequately simulated crop evapotranspiration and the volume of IRF and N loads in the IRF (errors
  • Authors:
    • Oliveira, H.
    • Quirino, F.
    • Eloy, M.
    • Cruz, L.
    • Tenreiro, R.
  • Source: European Journal of Plant Pathology
  • Volume: 133
  • Issue: 3
  • Year: 2012
  • Summary: Several outbreaks of bacterial wilt disease caused by the quarantine bacterium Ralstonia solanacearum were identified in Portugal. Intensive surveys recognized the bacterium as endemic in the main irrigated agricultural ecosystems. Between 1999 and 2006 all isolates of R. solanacearum were characterized as belonging to biovar 2A. In 2007, biovar 1 strains were recorded in potato fields under a confined area. A panel of 101 Portuguese isolates obtained from biotic and environmental samples was studied. Following a polyphasic approach, these isolates were analysed by SDS-PAGE of the whole cell proteins, MSP-PCR (csM13), rep-PCR (BOXA1R and ERIC-2) and FAFLP (EcoRI+0/MseI+C). A 750 bp sequence of endoglucanase ( egl) gene was studied for 17 representative isolates and 95 accessions retrieved from the GeneBank. Numerical analysis of protein profiles correlated quite well with biovar subphenotype, producing a unique megacluster ( r=71.1%). MSP-PCR was more discriminative ( r=62%). Rep-PCR approaches displayed higher polymorphism levels with ERIC 2 primer producing high diversity indexes (D and J′). FAFLP was the most reproducible method (95%) displaying 229 polymorphic characters and the highest evenness (J′). For all the methods small clusters disclosed a clonal origin for isolates with a common geographical origin/matrix. FAFLP identified an adaptative microevolution phenomenon for surface water strains. Polyphasic approach congruence highlighted the inability of individual methods to explain the whole diversity. Mr. Bayes egl-based phylogenetic tree allocated the 17 Portuguese isolates into the sub-clusters of narrow (nhr) and broad host range (bhr) of Phylotype II unveiling the epidemiological story of R. solanacearum in Portugal and identified different populations coexisting in the same habitats. This is the first report of the presence of R. solanacearum Phylotype II, bhr strains in Western Europe.
  • 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.