Abstract:In this paper two models are presented for calculating the hourly evapotranspiration E (W m 2 ) using the Penman-Monteith equation. These models were tested on four irrigated crops (grass, soya bean, sweet sorghum and vineyard), with heights between 0Ð1 and 2Ð2 m at the adult growth stage. In the first model (Katerji N, Perrier A. 1983. Modélisation de l'évapotranspiration réelle ETR d'une parcelle de luzerne : rôle d'un coefficient cultural. Agronomie 3(6): 513-521, KP model), the canopy resistance r c is parameterized by a semi-empirical approach. In the second model (Todorovic M. 1999. Single-layer evapotranspiration model with variable canopy resistance. Journal of Irrigation and Drainage Engineering-ASCE 125: 235-245, TD model), the resistance r c is parameterized by a mechanistic model. These two approaches are critically analysed with respect to the underlying hypotheses and the limitations of their practical application. In the case of the KP model, the mean slope between measured and calculated values of E was 1Ð01 š 0Ð6 and the relative correlation coefficients r 2 ranged between 0Ð8 and 0Ð93. The observed differences in slopes, between 0Ð96 and 1Ð07, were not associated with the crop height. This model seemed to be applicable to all the crops examined. In the case of the TD model, the observed slope between measured and calculated values of E for the grass canopy was 0Ð79. For the other crops, it varied between 1Ð24 and 1Ð34. In all the situations examined, the values of r 2 ranged between 0Ð73 and 0Ð92. The TD model underestimated E in the case of grass and overestimated it in the cases of the other three crops. The under-or overestimation of E in the TD model were due: (i) to some inaccuracies in the theory of this model, (ii) to not taking into account the effect of aerodynamic resistance r a in the canopy resistance modelling. Therefore, the values of r c were under-or overestimated in consequence of mismatching the crop height. The high value of air vapour pressure deficit also contributed to the overestimation of E, mainly for the tallest crop. The results clarify aspects of the scientific controversy in the literature about the mechanistic and semi-empirical approaches for estimating E. From the practical point of view the results also present ways for identifying the most appropriate approach for the experimental situations encountered.
The suitability of cloud-based irrigation technologies remains questionable due to limited information on their evaluation in the field. This study focussed on the on-field assessment of a smartphone irrigation scheduling tool—Bluleaf®—with respect to traditional water application practices. Bluleaf® uses weather, crop, soil, and irrigation system data to support a farmer’s decision on the timing and amounts of irrigation. The smartphone application was tested in Bekaa Valley, Lebanon, on durum wheat, a strategic Mediterranean crop, during the 2017 and 2018 growing seasons. The simulation results on soil water balance were in “acceptable to very good” agreement with the measured soil moisture values, with a root mean square error (RMSE) between 15.1 and 26.6 mm and a modelling efficiency (NSE) that ranged from 0.77 to 0.92. The appropriateness of the adopted smartphone irrigation scheduling was confirmed also by leaf water potential measurements and the Crop Water Stress Index (CWSI). A water saving of more than 1000 m3/ha (25.7%) was observed with Bluleaf® with respect to traditional irrigation scheduling. Therefore, new technologies could bring about substantial benefits to farmers and support water saving efforts in the Mediterranean region.
Variable rainfall, water stress, and spring frost are the main challenges for cereal growers in the Mediterranean region. The potential of wheat and barley to adapt to contrasting weather conditions was investigated through the adoption of no-till, supplemental irrigation and drought tolerant cultivars over a period of three years. Seasonal precipitation was 732, 336 and 685 mm in the first, second and third seasons, respectively. The second and third seasons were characterized by the occurrence of spring frost. No tillage did not affect productivity in either crop, while supplemental irrigation increased yield only in barley. For wheat, the grain yield was 60 and 43% respectively lower in the second and third seasons than in the first season. For barley, grain yield was 43% higher in the first season than the other two. The negative effect of frost on wheat yield was indirectly assessed by crop growth simulation. Principal component analysis shows that freezing temperatures associated with spring frost and rainfall both dictated crop growth and productivity.
Most of Southern Mediterranean water courses suffer from numerous types of pollution. This study presents a comprehensive performance assessment of a pilot CW system for removing various contaminants from the Litani River, Lebanon. The physico‐chemical, pathogens and trace metal parameters were analyzed for river water as well as for the wetland effluent. Results revealed that the average removal efficiencies were 87.01% for COD, 64.99% for BOD5, 86.18% for TSS, 43.11% for NO3N, 34.82% for NH4N, 55.07% for PO4P and 73.05% for K. The removal efficiency of faecal coliforms was around 99.84%. Influent and effluent heavy metal pollution (Cu, Pb, As and Ni) concentrations greatly exceeded the range of the environmental limit values due to industrial emissions in river water. CWs seem to be a promising green technology for Lebanon for the reduction of bacterial contamination. Further studies are required to improve treatment modules for different pollutants, including metals.
The use of polluted water to irrigate is an increasing problem in the developing world. Lebanon is a case in point, with heavily polluted irrigation waters, particularly in the Litani River Basin. This study evaluated the potential health risks of irrigating vegetables (radishes, parsley, onions, and lettuce) using three water sources (groundwater, river water, and treated wastewater) and three irrigation methods (drip, sprinkler, and surface) over two growing seasons in 2019 and 2020. Water, crop, and soil samples were analyzed for physicochemical parameters, pathogens, and metals (Cu, Cd, Ni, Cr, and Zn). In addition, the bioaccumulation factor, estimated dietary intakes, health risk index, and target hazard quotients were calculated to assess the health risk associated with metal contamination. The study showed that, for water with less than 2 log E. coli CFU/100 mL, no pathogens (Escherichia coli, salmonella, parasite eggs) were detected in irrigated vegetables, irrespective of the irrigation method. With over 2 log E. coli CFU/100 mL in the water, 8.33% of the sprinkler-and surface-irrigated vegetables, and 2.78% of the drip-irrigated root crops (radishes and onions), showed some degree of parasitic contamination. E. coli appeared only on root crops when irrigated with water having over 3 log CFU/100 mL. The concentrations of most metals were significantly lower than the safe limits of the FAO/WHO of the Food Standards Programme Codex, except for zinc and chromium. The trends in the bioaccumulation factor and the estimated dietary intakes of metals were in the order of Cu < Cd < Ni < Cr < Zn. The target hazard quotient values for all metals were lower than 1.0. Under trial conditions, the adoption of drip irrigation with water with less than 3 log E. coli CFU/100 mL proved to be safe, even for vegetables consumed raw, except for root crops such as onions and radishes that should not be irrigated with water having over 2 log E. coli CFU/100 mL. Treated wastewater had no adverse effect on vegetable quality compared to vegetables irrigated with other water sources. These results support efforts to update the Lebanese standards for water reuse in agriculture; standards proposed in 2011 by the FAO, and currently being reviewed by the Lebanese Institution of Standards. This research will inform a sustainable water management policy aimed at protecting the Litani River watershed by monitoring water quality.
This study investigated the effect of different water quality regimes [Freshwater (FW), treated wastewater (TW) and alternating FW and TW (FW‐TW)] on drip‐irrigated table grape yield, quality and microbial contamination. Water and soil samples were analysed. In addition, grape samples were harvested for quantitative and qualitative evaluation. The results showed that the plants irrigated with TW and those irrigated with alternating FW and TW gave 19.57 and 14.95% higher marketable yield, respectively, than plants irrigated with FW. Total soluble sugars, total titratable acidity and sweetness ranged, respectively, between 18.43–20.13, 0.69–0.81% and 21.52–29.19, and were within the desirable levels for table grape harvest. In addition, there was no significant difference in terms of total phenols and mineral composition of berries, leaves, peduncle and pedicels. Finally, table grapes did not present any bacterial contamination which confirm the importance of the adopted irrigation regime for a safe wastewater reuse in agriculture.
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