مجله پژوهش آب در کشاورزی
سال سی و پنجم شماره 1 (بهار 1400)

In this research, the status of water productivity for wheat production and strategies to increase water productivity in different quantitative conditions of water was determined and analyzed in the irrigation district of Sistan Dam. In this regard, the SWAP simulation model was calibrated and validated by considering the current water resources operation, various quantities of irrigation water, and use of field information. Water production functions were used to determine the irrigation schedule (time and depth) for wheat crop. The results of field measurements in the crop year 2016-2017 in the irrigation district showed that farmers irrigate wheat on average four times in the current conditions. Farmers' average crop yield and water productivity were about 1450 kg/ha and 0.41 kg/m3, respectively. These results show that available water is not appropriately used and should be addressed with practical solutions to improve water productivity. The validation and calibration results of the SWAP model also showed the high accuracy of the model in the case study. The results of different management scenarios of eliminating some irrigation shifts compared to the existing conditions indicated that, although there was no significant difference in water productivity, crop yield decreases about 37%. The results of evaluating the scenarios of reducing the depth and frequency of irrigation (using 640 mm per season and applying 40 mm at each shift) showed that, with reliable and timely water supply and more frequent irrigation, water productivity could be increased by 30% compared to the baseline scenario; and crop yield can be doubled. In these scenarios, the presence of adequate moisture in the plant's root zone increases the yield, and the amount of deep percolation is greatly reduced. The amount of water used by farmers is excessive for various reasons. Therefore, it is recommended to train farmers on how to improve irrigation and crop management according to the water available in the irrigation district, so that they can distribute water according to the real needs of the plant and irrigate at the right time and sufficient quantity.

Lettuce is one of the most important leafy vegetables used primarily for fresh and salad applications. The purpose of this study was to investigate the effect of different levels of water and nitrogen on lettuce yield and find the best irrigation and nitrogen fertilizer practices for producing this crop in drip irrigation. Iceberg variety of lettuce was planted in 2018 with three irrigation treatments (I1, I2 and I3 to provide 100%, 80%, and 60% of crop evapotranspiration, ETa, respectively) and four nitrogen treatments (N1, N2, N3, and N4 to provide 105, 70, 35 and zero kg of nitrogen per hectare in total, respectively). In 2019, two irrigation treatments (I1 and I3) and two nitrogen treatments (N1 and N4) were used. The experiment had a randomized complete block design with three replications. The results indicated that the effect of irrigation and nitrogen treatments and their interactions on the marketable yield of lettuce; but the dry matter produced was only affected by irrigation and nitrogen treatments. Maximum marketable yield and dry matter production were 66.1 ton.ha-1 and 2728.2 kg.ha-1 for full irrigation treatment with 105 kg.ha-1 nitrogen (I1N1) treatment, respectively. The minimum marketable yield and dry matter were 37.5 ton.ha-1 and 1929.6 kg.ha-1 for 60% ETa treatment with 35 kg.ha-1 nitrogen (I3N3) treatment, respectively. The maximum and minimum irrigation water productivities for marketable yield were 21.63 and 15.38 kg.m-3 for I2N1 and I3N3 treatments, respectively. The linear and nonlinear production functions of yield-water and yield-nitrogen were obtained for lettuce variety Iceberg, which can be used in similar environmental conditions in research and practical applications.

This research was performed to improve water productivity by changing a number of farmers' field practices such as tillage, dimensions of the irrigation borders, using newly released plants varieties, and improving fertilizer management in eight farms located in the Oskoo, Ajabshir, and Bonab cities, all parts of the eastern Uromieh Lake Basin, during 2015-2016 growing season. The adopted farm practices were applied in the treatment farms, while in the control farms, all the farming operations were implemented according to the local traditional practices. In all farms, the flow rates diverted to each farm, the soil moisture content in the root zone during the growing season, and indices related to the growth and yield of crops were measured. The indices of water productivity (WP), water use efficiency (WUE) and water economic productivity (WPe) were calculated. Water consumption was lower up to 9% while crops yields of the treatment farms were higher up to 34%, as compared with the control farms. According to the results, on average, implementation of applied technologies in the treatment farms increased WP, WUE, and WPe by 38%, 31%, and 56 %, respectively, as compared to the control farms.

Pressurized irrigation methods can be a suitable solution for optimal use of water resources, provided that the selection, design, implementation and operation of irrigation systems are done with sufficient care and according to the principles. In decision-making and implementation of pressurized irrigation systems at the sub-regional and regional scale, several factors such as water, soil and climate along with socio-economic factors are of particular importance. Dez Plain (including Lor, Dimcheh, West Dez, East Dez and Sabili plains) is the largest plain and one of the most important agricultural hubs in Khuzestan Province. In this study, using AHP in GIS software, the suitability of various areas for implementing different irrigation systems (localized, solid set, wheel move, centre pivot, linear, Gun, low-pressure, and surface) was investigated in Dez Plain. For this purpose, effective criteria including socio-economic and field physical conditions were considered for implementation of each irrigation method. Socio-economic criteria included four sub-criteria, namely, operation and maintenance, costs, laborers skills, and local culture, and physical conditions included water, climate, soil, and topography. The final location map was prepared in GIS software. According to the results, Dez Plain areas with high suitability for each methods were as follows: 62.77% for all sprinkler systems, 14.6% for localized irrigation, 14.3% for low-pressure irrigation, and 8.3% for surface irrigation. Among all irrigation methods, the solid-set sprinkler obtained the highest score in all parts of the study area and, in total, 15.04% of the whole plain is highly suitable for this system.

The main purpose of this study was to estimate the coefficients of different equations of water infiltration into soil, including Philip, Kostyakov, Kostyakov- Louise, Horton, and SCS to estimate the infiltration rate and potential for runoff in long-duration rainfall in two land uses (rangeland and agricultural) and three soil textures (loam, clay loam ,and silty clay loam). These models were fitted to the measured infiltration data to estimate the model parameters and find a suitable model for this region. After estimating the parameters, the infiltration rates for 2, 4 and 24 hours were calculated using the infiltration rate equations of each model. For this purpose, the infiltration data were obtained by double rings method from 16 point of different regions in the basin. The parameters of these models were then obtained, using least square optimization method. In order to evaluate the accuracy of the models, the coefficient of determination (R2), Nash Sutcliffe (NSE) efficiency, root mean square error (RMSE) and mean error (ME) were calculated. Comparisons of the mean of evaluation statistics using the Tukey method showed that the method of estimating cumulative infiltration in the Kostyakov-Louise model had a more-stable trend compared to other models and was evaluated as the best in most soil texture classes and land uses. Means comparisons showed that despite the differences between the models in estimating the cumulative infiltration, the differences between the models in estimating the infiltration rate were not significant and were in the same group. Regardless of the model used, soil texture and land use are the two main factors affecting the final infiltration rate. According to the results, the rate of infiltration with time in agricultural use has significant changes, such that, in this use, it was initially high and decreased sharply with increasing time from 2 hours to 24 hours. In order to reduce the weakening effects of agricultural activities on soil quality and to increase the infiltration rate in long-duration rainfall and reduce runoff, management activities such as expansion of conservation agriculture, no-tillage, and minimum tillage farming operations will play a very effective role.