Estimation of actual evapotranspiration for a drip-irrigated Merlot vineyard using a three-source model

A study was performed in order to evaluate the three-source model (Clumped model) for direct estimation of actual evapotranspiration (ET_a) and latent heat flux (LE) over a drip-irrigated Merlot vineyard trained on a vertical shoot positioned system (VSP) under semi-arid conditions. The vineyard, with an average fractional cover of 30%, is located in the Talca Valley, Region del Maule, Chile. The performance of the Clumped model was evaluated using an eddy covariance system during the 2006/2007 and 2007/2008 growing seasons. Results indicate that the Clumped model was able to predict ET_a with a root mean square error (RMSE), mean bias error (MBE), and model efficiency (EF) of 0.33, −0.15 mm day⁻¹ and 74%, respectively. Also, the Clumped model simulated the daytime variation of LE with a RMSE of 36 W m⁻², MBE of −8 W m⁻², and EF of 83%. Major disagreement (underestimated values) between observed and estimated values of ET_a was found for clear days after rainfall or foggy days, but underestimated values were less than 10% of the data analysis. The results obtained in this study indicate that the Clumped model could be used to directly estimate vine water requirements for a drip-irrigated vineyard trained on a VSP. However, application of the Clumped model requires a good characterization of the drip-irrigated vineyard architecture.     

Surface velocity coefficients for application of the float method in rectangular and compound open channels

A three-dimensional mathematical hydraulic model was applied to calculate velocity profiles and discharge under steady, uniform flow conditions in rectangular and compound open-channel cross sections. The velocity profiles were used to calculate surface velocity coefficients for use with the float method for discharge estimation in the field. Surface velocity coefficients were calculated at increments of one-eighth of the base width from the vertical walls to the center of the cross section, and submergence of the float object from 0 to 30 cm, with a 5-cm depth increment. Model results were summarized to show the relationship between surface velocity coefficient and channel characteristics compared to values published by the US Bureau of Reclamation (USBR). For rectangular cross sections, the coefficients from the model are generally higher than the published USBR values. But the coefficients from the model and USBR are in very close agreement for the tested compound cross sections. The published coefficients by the USBR are a function of only average water depth. However, the model results show that the coefficient is also related to channel size, cross-sectional aspect ratio, surface roughness height, float submergence and lateral location of the float object. These factors should be included in the determination of the surface velocity coefficient to improve the discharge estimations from the application of the float method.     

Response of alfalfa (<Emphasis Type="Italic">Medicago sativa</Emphasis> L.) to diurnal and nocturnal saline sprinkler irrigations. II: shoot ion content and yield relationships

When using saline waters, sprinkling irrigation at night is a recommended practice to reduce evaporation, salt absorption by the wetted leaves and its negative effects on crops. We measured shoot ion concentrations (Cl⁻, Na⁺ and K⁺) and total dry matter (TDM) in alfalfa subject to diurnal and nocturnal saline sprinkler irrigations and established potential relationships among them. The work was carried out along the 2004–2006 growing seasons using EC waters from 0.5 to 5.6 dS m⁻¹. Saline sprinkling irrigations linearly increased shoot Cl⁻ and Na⁺ and decreased shoot K⁺. Even though daytime evaporation was much higher than nigh-time, shoot ion accumulation and TDM were similar in the diurnal and nocturnal irrigations. The salinity tolerance of alfalfa decreased in year 2006 due to increases in shoot Cl⁻ and, particularly, shoot Na⁺. The lower threshold for shoot Na⁺ (276 meq kg⁻¹) than for shoot Cl⁻ (726 meq kg⁻¹) shows that alfalfa is more sensitive to Na⁺ than to Cl⁻, and that Na⁺ accumulation is the preponderant cause of alfalfa yield decline after 3 years of sprinkling with saline waters.     

Response of apricot trees to deficit irrigation strategies

During four growing seasons, 10-year-old apricot trees (Prunus armeniaca L., cv. ‘Búlida’) were submitted to three different drip irrigation regimes: (1) a control treatment, irrigated at 100% of seasonal crop evapotranspiration (ETc), (2) a continuous deficit irrigation (DI) treatment, irrigated at 50% of the control treatment, and (3) a regulated deficit irrigation (RDI) treatment, irrigated at 100% of ETc during the critical periods, which correspond to stage III of fruit growth and 2 months after harvest (early postharvest), and at 25% of ETc during the rest of the non-critical periods in the first two growing seasons and at 40% of ETc in the third and fourth. Soil–plant–water relation parameters were sensitive to the water deficits applied, which caused reductions in leaf and soil water potentials. The longer and severer deficits of the RDI treatment decreased fruit yield in the first two seasons. The RDI treatment pointed to two threshold values that defined the level at which both plant growth and yield were negatively affected with respect to the control treatment: (1) a predawn leaf water potential of around −0.5 MPa during the critical periods, and (2) a 22% drop in irrigation water. The total yield obtained in the DI treatment was significantly reduced in all the years studied due to the lower number of fruits per tree. No changes in the physical characteristics of fruits were observed at harvest. RDI can be considered a useful strategy in semiarid areas with limited water resources.     

Effects of water table management on soil salinity and alfalfa yield in a semi-arid climate

A lysimeter experiment was conducted to investigate the effect of water table management (WTM) on distribution of soil salinity and annual alfalfa (Medicago scutellata) yield. Subirrigations with three levels of water table namely, 0.5 (WT0.5), 0.7 (WT0.7), and 1.0 m (WT1.0) and a free drainage (FD) conventional irrigation treatment were selected for this study. All treatments were arranged in a complete randomized block design with three replicates. The results of this study indicated that the average soil electrical conductivity of the saturated extract (ECe) in the root zone gradually increased and exceeded the designated crop threshold value (4 dS/m) after the first forage harvest in subirrigated lysimeters. A higher salt accumulation was observed at the WT0.5 treatment. The average dry matter yield of annual alfalfa in WT0.5 and WT0.7 treatments was found to be 52 and 73% higher compared with the control treatment, respectively.     

FSWM: A hybrid fuzzy-stochastic water-management model for agricultural sustainability under uncertainty

A hybrid fuzzy-stochastic water-management (FSWM) model is developed for agricultural sustainability under uncertainty, based on advancement of a multistage fuzzy-stochastic quadratic programming (MFSQP) approach. In MFSQP, uncertainties presented in terms of fuzziness and randomness can be incorporated within a multilayer scenario tree, such that revised decisions are permitted in each time period based on the realized values of the uncertain events. Moreover, fuzzy quadratic terms are used in the objective function to minimize the variation of satisfaction degrees among the constraints; it allows an increased flexibility in controlling the system risk in the optimization process. Results of the case study indicate that useful solutions for the planning of agricultural water management have been obtained. In the FSWM model, a number of policies for agricultural water supply are conducted. The results obtained can help decision makers to identify desired water-allocation schemes for agricultural sustainability under uncertainty, particularly when limited water resources are available for multiple competing users.     

Estimating reference evapotranspiration with atmometers in a semiarid environment

Reference evapotranspiration (ET₀) estimations require accurate measurements of meteorological variables (solar radiation, air temperature, wind speed, and relative humidity) which are not available in many countries of the world. Alternative approaches are the use of Class A pan evaporimeters and atmometers, which have several advantages compared to meteorological stations: they are simple, inexpensive and provide a visual interpretation of ET₀. The objectives of the study were to compare the evaporation from atmometers (ET_gage) with the evapotranspiration estimated by the FAO-56 Penman-Monteith equation (ET_0PM) and to evaluate the variability between three modified atmometers of a commercial model. Comparison between daily ET_gage measured by the atmometer and ET_0PM showed a good correlation. However, ET_gage underestimated ET_0PM by approximately 9%. Differences between ET_gage and ET_0PM ranged from −2.4 to 2.2 mm d⁻¹ while the mean bias error was −0.41 mm d⁻¹. Underestimations occurred more frequently on days with low maximum temperatures and high wind speeds. On the contrary, atmometer overestimations occurred on days with high maximum temperatures and low wind speeds. Estimates of ET₀ using the atmometer appeared to be more accurate under non-windy conditions and moderate temperatures as well as under windy conditions and high temperatures. Atmometers 2 and 3 overestimated the evaporated water by atmometer 1 with a maximum variability of cumulative water losses of 4.5%. A temperature-based calibration was performed to improve the atmometer accuracy, using maximum temperature as an independent variable, with good results.     

Mineral content of three olive cultivars irrigated with treated industrial wastewater

The reuse of saline treated industrial wastewater generated by textile firms mixed with municipal domestic effluent for irrigation was used to asses its effect on the mineral content of three olive (Olea europaea L.) cultivars under greenhouse and field conditions during two complete vegetative cycles. Chemical analysis of the treated wastewater indicated that the element concentrations fall within the permissible range of irrigation water used for plants. However, little impermissible accumulation of Na and Mg higher than the recommended maximum concentration was observed. Irrigation water with six electrical conductivities (EC = 0.78, 1.0, 2.0, 3.0, 4.0 and 5.0 dS m⁻¹ in treatments T₀, T₁, T₂, T₃, T₄, T₅, respectively) were compared in the greenhouse experiment. The olive trees in the field experiment were trickle irrigated with potable water and treated wastewater (average EC = 4.2 dS m⁻¹). The results of the greenhouse experiment showed that leaf N, Cu, Mn, Fe, Pb, and Na contents increased with increasing salinity of the treated wastewater. This increase was accompanied with a decrease in K and Mg contents. Leaf Ca and Cl concentrations were not considerably affected. Ion analysis in roots indicated that the contents of P, Na, Cl, Mn, and Pb increased while K decreased as treated wastewater salinity increased. Consequently, in most cases T₄ and T₅ gave a highly significant increase or decrease in accumulation of the previously mentioned minerals. A considerable variation in the studied cultivars was noticed. ‘Nabali’ was considered the most tolerant cultivar for the high salinity levels of the treated wastewater; its transporting selectivity of Na from root to leaf was higher and more Na was retained in the roots. Tissue analysis of leaves indicated that the element concentrations were within the adequate levels except those of Fe in ‘Nabali’ and ‘Manzanillo’, Na in ‘Improved Nabali’ and Cu in ‘Nabali’ and ‘Manzanillo’. In view of these findings, the negligible accumulation of minerals in leaves and roots indicated that this kind of textile effluent can be used as a valid alternative for irrigation of olive orchards with continuous monitoring of mineral levels.     

三种沙棘浆果成熟过程中的糖、有机酸、黄酮醇和类胡萝卜素组分的变化

在Askola、Hergo和Leikora三个德国沙棘品种的浆果中,根据不同采集时间来测定其可溶性固形物,糖,有机酸,黄酮醇和类胡萝卜素的含量,用以提供一个更为完善的浆果成熟期内沙棘品质变化的情况。沙棘浆果成熟期内主要有机酸是苹果酸（1940-4660mg／100g）,奎宁酸（810～2820mg／100g）,维生素C（180～370mg／100g）和柠檬酸（90～160mg／100g）。在这3个沙棘品种中所有有机酸的浓度在成熟过程中呈现显著下降趋势。而其糖类如葡萄糖（0．26～2．10g／100g）和果糖（0．14～0．54g／100g）在3个品种中成分变化略有不同。所有3个沙棘品种维生素C浓度在成熟过程中呈现下降趋势。含有的主要黄酮醇是异鼠李素（350-660mg／kg）,槲皮素（30～100mg／kg）和山奈酚（2-5mg／kg）。在3个沙棘品种中黄酮醇浓度在成熟过程中显示出不同的变化趋势。主要类胡萝卜素是玉米黄素（30～150mg／kg）,β-胡萝卜素（3～50mg／kg）和β-隐黄质（5～19mg／kg）。基因型对类胡萝卜素的收集和类胡萝卜素的形态都有影响,但在3个沙棘品种成熟期间类胡萝卜素浓度呈现增加趋势。在成熟期间抗氧化剂的分类表现出不同的组成变化,最大浓度也出现在不同的收获期。     

Changes in epidemiological patterns of sea lice infestation on farmed Atlantic salmon, Salmo salar L., in Scotland between 1996 and 2006

Analyses of a unique database containing sea lice records over an 11 year period provide evidence of changing infestation patterns in Scotland. The data, collected from more than 50 commercial Atlantic salmon farms, indicate that both species of sea lice commonly found in Scotland, Lepeophtheirus salmonis and Caligus elongatus, have declined on farms over the past decade. Reductions for both species have been particularly marked since 2001 when more effective veterinary medicines became available. Treatment data were also available in the database and these show a growing trend towards the use of the in-feed medication emamectin benzoate (Slice), particularly in the first year of the salmon production cycle. However, this trend towards single product use has not been sustained in 2006, the latest year for which data are available. There is some evidence of region to region variation within Scotland with the Western Isles experiencing higher levels of infestation. However, compared to the levels observed between 1996 and 2000, all regions have benefited from reduced lice infestation, with the overall pattern showing a particular reduction in the second and third quarters of the second year of production.