Masoud Mohammadi; K Davary; Bizhan Ghahraman
Abstract
Considering limitations of agricultural productions in arid and semi-arid regions, optimization of irrigation depth and leaching is very important. In this study, calibrated and validated AquaCrop model was used in order to optimize irrigation water depth and leaching for two varieties of winter wheat ...
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Considering limitations of agricultural productions in arid and semi-arid regions, optimization of irrigation depth and leaching is very important. In this study, calibrated and validated AquaCrop model was used in order to optimize irrigation water depth and leaching for two varieties of winter wheat (Ghods and Roshan) in Birjand region and one variety of wheat (spring Roshan) in Mashhad region. For winter wheat, irrigation treatments included 125%, 100%, 75% and 50% of water requirement and water salinities of 1.4, 4.5, and 9.6 dS/m for winter wheat. For spring wheat, irrigation treatments consisted of 100%, 90%, 65%, and 40% of water requirement and water salinities of 0.5, 0.9, 5.25, 8.6, and 10 dS/m. The coding written in Matlab program was linked to the AquaCrop in order to achieve the optimized values of irrigation and leaching in the land constraint conditions. The optimization results showed that net profit for the best irrigation and leaching management at all salinity levels and different wheat varieties, except for salinity levels of 8.6 and 10 dS/m in the spring Roshan variety and level of 9.6 dS/m in the winter Roshan variety, was more than the current management in field conditions. The increases in profits in optimal management compared to the current management for Ghods variety at the salinity levels of 1.4, 4.5, and 9.6 dS/m were 51.4%, 78.9%, and 142.5%, respectively. For the same salinity levels for Roshan variety, the increments were 42.7%, 20.8% and -0.3%, respectively. The increase in profits in optimal management compared to the current management for the spring Roshan variety at the salinity levels of 0.5, 0.9, 5.25, 8.6 and 10 dS/m, were 5%, 13.2%, 34.3%, -27.7%, and -51.4%, respectively. In general, the results show that in the regions where drainage problem due to irrigation water is an important environmental problem and causes dissatisfaction among the downstream farmers, applying less water and accepting negligible decrease in the benefits (minimum 0 and maximum 29%) could resolve the problem.
Ehsan Tavakoli; Behzad Ghorbani; m r; h s; b gh
Abstract
Increasing conveyance efficiency and reducing water loss in distribution canals are very important. The current study aimed at investigating and comparing empirical equations and SEEP/W model for estimating seepage of earth channels. For this study, the earth canal of Boldaji, constructed in loamy soil ...
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Increasing conveyance efficiency and reducing water loss in distribution canals are very important. The current study aimed at investigating and comparing empirical equations and SEEP/W model for estimating seepage of earth channels. For this study, the earth canal of Boldaji, constructed in loamy soil and located downstream of modern irrigation and drainage network of Gandoman and Boldaji, Chaharmahal and Bakhtiari province, was chosen. Using dimensional similitude equations and considering 0.13 as scale ratio, the dimensions and discharges of the mentioned channel were applied to the laboratory model. In this study, 9 discharges (40-161 L/s) were converted to the applicable discharges of the model. Experiments carried out for 4 different water table depths and trapezoidal and triangular cross sections with 3 replications. Furthermore, by employing modified empirical models of Moritz, Ingham, India, Molesworth and Yennidumia, Offengenden, and Davis-Wilson, besides SEEP/W model, the amounts of seepage in the lab model were estimated. The results showed that for all investigated conditions and considering R2, r, RMSE, and MAE, Moritz presented the closest and the most accurate estimates of seepage (R2=0.992, r=0.996, RMSE=0.48 and MAE=0.44 lit/m2/min). Moreover, due to poor results of Molesworth and Yennidumia and Indian equations, they are not suggested for the study area.Although SEEP/W demonstrated appropriate performance for trapezoidal cross section, it did not show promising results for the triangular one. Considering the lower costs and shorter time as the results of utilizing dimensional analysis, it is recommended for controlled laboratory conditions in other similar regions.
Mohammad Mehdi Nakhjavanimoghaddam; b gh; gh z
Abstract
Recently, the main challenge of agricultural sector is improvement of crop water productivity (CWP). In Iran, unfortunately up to now, determination and analysis of water productivity indicators in agricultural sector has not been considered seriously, which has led to the uncertainty of proper water ...
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Recently, the main challenge of agricultural sector is improvement of crop water productivity (CWP). In Iran, unfortunately up to now, determination and analysis of water productivity indicators in agricultural sector has not been considered seriously, which has led to the uncertainty of proper water consumption in agriculture. This study was aimed to evaluate wheat water productivity under different irrigation managements in Iran and determine the suitable irrigation depth for wheat in situation of water resource limitations. Based on the experiments conducted in eight research stations located in different regions of the country during 1998-2012 for wheat, it was found that the range of CWP was 0.3-1.5 kg m-3 which was wider than that reported earlier by the FAO, i.e. 0.8-1.0 kg m-3. Nevertheless, it is in the range proposed by Zwart and Bastiaanssen in 13 countries from five different continents. The wide ranges of CWP indicate tremendous opportunities for increasing the agricultural productions with less water. The maximum measured wheat water productivity (CWPI) for irrigation water alone and for irrigation+ effective rainfall (CWPI+Re) was 2.1 and 1.5 kg m-3, respectively, in Karaj region, where drip irrigation and deficit irrigation management were applied. Also, the minimum measured wheat CWPI and CWPI+Re was observed in Kerman region under surface irrigation. The maximum measured wheat CWPI and CWPI+Re in Mashhad region was 1.9 and 1.5 kg m-3, respectively, under deficit irrigation management. The results showed that wheat CWPI and CWPI+Re of 1.6 and 1.1 kg m-3 could be considered as the optimum levels in cropping system of Mashhad region. The depths of irrigation water alone and total applied water (irrigation +effective rainfall) for optimum level of wheat CWP under deficit irrigation management were 300 and 420 mm, respectively.
Ameneh Miananadi; a a; Hossein Sanaeinejad; b gh; kamran davary
Abstract
The SEBAL algorithm is used to estimate spatial distribution of actual evapotranspiration using remote sensing imageries of MODIS or Landsat. Despite having a better spatial resolution than MODIS imageries (30 m instead of 1000 m), Landsat imageries do not have an appropriate temporal resolution (every ...
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The SEBAL algorithm is used to estimate spatial distribution of actual evapotranspiration using remote sensing imageries of MODIS or Landsat. Despite having a better spatial resolution than MODIS imageries (30 m instead of 1000 m), Landsat imageries do not have an appropriate temporal resolution (every 16 days instead of daily). On the other hand, the daily imageries of MODIS can be difficult to use under cloudy condition. Additionally, it is also a time-consuming process to interpret all the imageries. In this research, we chose the appropriate imageries from MODIS to be able to monitor the sudden weather changes as well as rainfall events and to reduce the interpretation time, while keeping the important information of the daily MODIS imageries in order to obtain the better actual evapotranspiration estimates. Due to the importance of hot and cold pixel selection, whose selection needs time and proficiency, we applied the automated method of hot and cold pixel selection (without user-intervention) using Landsat imageries. To integrate evapotranspiration over time, we used linear-logarithmic interpolation method in addition to linear interpolation method. The estimated actual evapotranspiration by SEBAL was compared to the estimated actual evapotranspiration from water balance equation and SWAT model for 3 years including a wet year (2004-2005), a normal year (2005-2006) and a dry year (2007-2008) in the Neishaboor-Rokh watershed. Furthermore, we used the Budyko framework to validate the evapotranspiration estimated by SEBAL and SWAT. The results showed that in comparison to SWAT, the linear-logarithmic interpolation method performed better than the linear method to estimate evapotranspiration. For linear-logarithmic method, RMSE, MBE, and MAE were 20.4, 0.09, and 18.4 mm year-1, respectively; and for the linear method, they were 21.8, -2.4, and 20.8 mm year-1, respectively. The results also demonstrated that the SEBAL algorithm with automated cold and hot pixel selection is able to have a good estimate of actual evapotranspiration at annual time scale and watershed scale. But, the algorithm does not perform well at HRUs and monthly scale in comparison to SWAT model. Results showed that by taking irrigation into account, evaporation estimated by SEBAL and SWAT follows the Budyko framework.
Masoud Mohammadi; Bijan Ghahreman; Kamran Davari; Majid Vazifehdoost; Hamideh Noori
Abstract
Field studies to determine optimum amount of water required for maximum production are time-consuming and expensive. Therefore, in this study the agro-hydrological model SWAP 3.03 was used to simulate winter wheat yield under different qualities and quantities of irrigation water and to determine water-salinity-yield ...
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Field studies to determine optimum amount of water required for maximum production are time-consuming and expensive. Therefore, in this study the agro-hydrological model SWAP 3.03 was used to simulate winter wheat yield under different qualities and quantities of irrigation water and to determine water-salinity-yield optimum function. Irrigation treatments consisted of four water salinity levels (S1=0.7, S2=2, S3=4 and S4=6 dS/m), three amounts of water (W1=80, W2=100, and W3=120 mm), and six levels of management allowed depletion (MAD1=0.3, MAD2= 0.4, MAD3= 0.5, MAD4= 0.6, MAD5= 0.7 and MAD6= 0.8). Yield and water use efficiency values were determined in different modes and the best MAD value obtained was 0.5. Yield data were fitted to different forms of production functions (simple linear, logarithmic linear, quadratic and transcendental) and the best one was established based on sensitivity analysis. The maximum grain yield (6619 kg/ha) corresponded to W1S1MAD2 treatment and the minimum yield (2048 kg/ha) corresponded to W1S4 MAD3 treatment. The results showed that the quadratic production function was optimal for production and could be recommended. Investigation of the maximum values of error (ME) showed that the logarithmic linear and simple linear functions had the highest error. In the irrigation treatments, W1S1MAD3 and W1S1MAD4 with 0.61 kg /m3 had the highest water use efficiency. However, water use efficiency decreased when water stress and salinity increased. The iso-yield curve showed that by increasing amounts of irrigation, more saline water could be applied without a change in yield.