مجله پژوهش آب در کشاورزی
سال سی و سوم شماره 2 (تابستان 1398)

Pistachio is the most important export product of Iranian agricultural sector. This product is very important because of valuation, job creation, value added as well as tolerance to salinity and drought. The purpose of this study was to investigate and analyze the evapotranspiration of pistachio (ETc and ETa), gross water requirement (IWR), and depth or volume of water used in pistachios (AW) in several selected gardens in Bahadoran region of Yazd province. The study area is one of the pistachio growing centers in Yazd province. The results show that the total annual irrigation water depth in the selected orchards varies from 823 to 1600 mm (equal to 0.27 to 0.57 L/s/ha). However, due to the salinity of irrigation water and to overcome the problems of accumulation of salts in the soil, the hydromodule necessary to supply the water needed for pistachios varies from 0.6 to more than 1 L/s/ha. According to the critical condition of the water resources in the plain, it is virtually impossible to provide it. Also, by using Surface Energy Balance Algorithm, the actual evapotranspiration of pistachios during the growing season was 556 mm for the whole study area and 672 mm for the selected orchards. Regarding the comparisons between pistachio water demand, actual evapotranspiration, and volume of water used in the selected orchards, a managed deficit irrigation strategy can be recommended for the study area. Optimization of traditional irrigation systems, changes in water utilization system with the aim of reducing irrigation interval, considering the spatial variations of pistachio water requirement in the region, off-season leaching, and implementation of proper management at the orchard level are among the solutions that can be useful in overcoming the salinity and water shortage problems and prevent product loss.

Although climate change in most parts of the world has changed the amount of water consumed in agriculture, various data from FAO are still used in irrigation planning and in determining allocation of irrigation water. The aim of this study was to determine the accuracy of FAO global data for sugar beet crop coefficient in Ardabil plain. At first, parameters of the water balance equation including rainfall and irrigation, drained water, soil water storage, and sugar beet evapotranspiration were determined, using three volumetric lysimeters. After preparation of lysimeters, on May 2017, sugar beet was planted in the lysimeters and the surrounding area, and irrigated. Volumes of drainage water collected from the lysimeters after each irrigation and volumetric water content before each irrigation was measured. Finally, using the measured data, the water balance equation was completed for various time intervals and the plant evapotranspiration and crop coefficients were determined for different quadruple growth stages. Means comparison was performed using t student test at two probability levels of 1% and 5%. Results showed that total the seasonal evapotranspiration of sugar beet plant was 1013 mm. The average crop coefficients for the first, second, third, and the fourth growth stages and the whole growing period were 0.33, 0.9, 1.16, 0.88, and 0.9, respectively. At two probability levels of 1% and 5% and in all growth stages, the mean of measured crop coefficient values was not significantly different compared to the values provided by FAO. The measured crop coefficient values are in good agreement with the published FAO values, therefore, the published data by FAO can be used for irrigation scheduling in the studied area.

Some experiments were performed around the Agricultural and Natural Resources Research Station of Islamabad-Gharb city in order to determine the reaction of corn crop to deficit irrigation strategy and its effects on yield, yield components and water productivity (WP) under furrow irrigation. The research used randomized complete block design (as a composite analysis in two years (2015 and 2016)). The treatments included irrigation with 100%, 75%, 50% and 25% water requirement with three replications. The SC704 Variety was used for planting corn. To compare the treatments, the 7 parameters of the performance components were considered, using analysis of variance (ANOVA). The results showed that the weight of corns in the first treatment was significantly superior to other treatments. Nevertheless, there was no significant difference in total weight of ears, ears length, seeds number per row, number of ear rows, wood weight and the weight of 1000 corns between treatments of 100% and 75% water requirement. However, in all measured attributes, there were significant differences between the other two treatments and the first and second treatments. Regarding water productivity in terms of total weight and grain weight of ears, the 75% treatment was superior to other treatments and had significant differences with the other treatments. In the treatment with 75% water requirement, WP was 0.8 kg/m3 based on the total weight of the grains, and based on the seed weight, it was 0.62 kg/m3, which were, respectively, 17% and 13% higher than the full irrigation treatment. The results showed that the highest water productivity was observed with about 30% deficit irrigation. It is to be noted that deficit irrigation may increase salinity of the root zone.

To investigate the effect of unconventional water and zeolite on yield and water use efficiency of sorghum, a split plot experiment was conducted based on randomized complete block design with 3 replications, at Gharakhil Agricultural Research Station in Ghaemshahr, Mazandaran Province. In this experiment, the main treatment was irrigation water quality (well water as control (W1); 75% well water and 25% seawater (W2); 25% well water and 75% seawater (W3); 100% treated urban wastewater alternated with 100% seawater (W4); 50% seawater and 50% urban treated wastewater (W5); irrigation with urban treated wastewater (W6)), and sub-treatment included three levels of zeolite as soil amendment (without zeolite Z1, calcic zeolite Z2, and potasic zeolite Z3). The results of data analysis showed that irrigation water quality treatments and zeolite levels had a significant (P<0.05) effect on plant yield. With increasing salinity, the yield of fresh and dry fodder sorghum decreased, but no significant difference was observed between treatments W5 and W4. The fresh and dry fodder yield in treated wastewater with calcic zeolite was higher than other treatments. The highest leaf area index was recorded in W6Z2 treatment (7.62) and the lowest was in W3Z1 treatment (3.80). The highest water use efficiency of fresh forage was observed in W6Z2 treatment (12.7 kg/m3) and the lowest in W3Z1 treatment (4.62 kg/m3).

Water stress, as the most important non-biological stress, has many undesirable effects on nutrients uptake, growth, and yield of higher plants. Nutrient such as nitrogen are effective against water stress and proper usage of nitrogen can prevent drastic reduction of yield under water stress conditions. This study was conducted to evaluate the combined effects of nitrogen and irrigation on the yield and quality of potato (Solanum tuberosum L.). The study was performed as a split-block based on randomized complete blocks design with factors of irrigation at four levels (0-3, 3-6, 6-9 and 9-12 meters’ distance from the main line source), and nitrogen at three levels (90, 135, and 180 kg per ha) using three replications and line source sprinkler irrigation system. Irrigation water of each level was measured by boxes that were fixed in the middle of each plot. The statistical analysis of results was done by the method described by Hanks. The results showed that application of nitrogen significantly increased yield, stem height, leaves number, water productivity, and leaf and tuber nitrogen concentration. Water deficit decreased yield, stem height, leaves number, and water productivity. The two-way interaction of nitrogen and irrigation was not significant on the measured attributes. The best treatment for water productivity (3.91 kg/m3 water) was using 621 mm irrigation and 180 kg N per ha. The highest amount of potato yield (42158 kg/ha) was obtained from application of 180 kg/ha nitrogen and 811 mm irrigation water.

Considering the great value of water, irrigation scheduling, and cultivation of medicinal plants, this research was conducted at the Faculty of Agriculture, Lorestan University, with the aim of scheduling irrigation of summer savory using CWSI and applying different levels of water stress under the condition of pot planting. In this research, seeds of summer savory were cultivated  with three replications under four irrigation treatments of 100%, 80%, 60%, and 40% of readily available water (RAW) (IR100, IR80, IR60 and IR40). Irrigation of the control treatment (IR100) was carried out when all the soil RAW was depleted. Irrigation of the other three treatments was carried out at the same time but with, respectively, 80%, 60%, and 40 percent of the volume applied to IR100.  The canopy cover temperature in IR100 and air temperature (dry and wet) were measured on the day after (8-14 o’clock) and before irrigation (12-15 o’clock) in order to construct the lower and upper limits base lines required to calculate CWSI. According to the result, the upper base line equation is (𝑇𝑐-𝑇𝑎) UL = 0.69, and the lower base line is (𝑇𝑐-𝑇𝑎) LL = 0.2787 - 0.1134 (VPD). Result showed that the effect of water stress on yield was significant. The highest yield was observed in IR100 (1.756 g / plant) and the lowest yield was observed in IR40 (1.421 g / plant). The crop water stress index (CWSI) of the four treatments in the day before irrigation was 0.19, 0.21, 0.28, and 0.46, respectively. According to this information, the permissible CWSI index for irrigation scheduling of summer savory growing in pots was 0.19. The result of means comparison indicated that differences between IR100 and IR80 in values of CWSI and canopy cover temperature were not significant, but they were significant between IR100, IR60 and IR40.  The increment of CWSI in IR80, IR60 and IR40 were 10%, 47%, and 142 percent relative to the IR100. In this research, a strong correlation (r= -0.978*) was obtained between CWSI and stomatal conductance.

In this research, the effect of different levels of irrigation water, nitrogen fertilizer, and cow manure on garlic was investigated. The experiments were carried out in a split-spilt plot design, with four levels of irrigation water depths (40%, 60%, 80% and 100% of the plant water requirement) in the main plots, three levels of nitrogen (50, 75 and 100% nitrogen) in the sub- plots, and three levels of manure (25, 32.5 and 50 ton/ha  cow manure) in the sub-plots. Nitrogen was applied in two stages and cow manure in one stage before planting. At the end of the experiment, parameters such as plant height, weight, and number of garlic, yield, and irrigation water productivities were measured. The results showed that the effects of irrigation water, nitrogen fertilizer, and manure were significant (p< 1% and <5%) on all parameters. The highest yield was obtained from 100% fertilizer application and 100% water requirement, but no significant effect was observed between treatments of 100 and 80% of water requirement. The highest amount of irrigation water utilization was obtained at irrigation level of 60% and fertilizer level of 100% (1.48 kg/m3/ha). In this regard, there was no significant difference between treatments of 60% and 80% of water requirements. The amount of allicin was reduced by reducing irrigation water and reducing fertilizer use. Increasing nitrogen fertilizer up to 75% of fertilizer requirement, amounting to 150 kg/ha, resulted in increase of allicin, but higher amounts resulted in decrease of allicin content. Therefore, due to shortage of water in the region, irrigation of this crop can be done with 80% of the plant's water requirement, without a significant effect on the yield.

Climate change is one of the natural occurrences that cause temperature rise, reduced rainfalls, change in water balance, decline in production level, and frequent droughts. Therefore, predicting and evaluating the effects of climate change and drought could be very effective for future decision making. According to this approach, in this study, the effects of climate change and drought on cropping pattern and income risk effects in Qazvin plain were investigated. The LARS-WG model was used to simulate climate variables (temperature and precipitation) in the future, as well as their changes in the A1B, A2 and B1 climate scenarios. Also, the Standard Precipitation Index (SPI) was used to determine drought periods and water volume changes. Then, using the mathematical programming approach and compilation of the MOTAD-TARGET with PMP model, the cropping pattern was simulated in climate scenarios and drought periods and the risk effects of these scenarios were investigated. The results show that in all three climate scenarios, temperature increases and precipitation decreases, and cropping pattern changes toward crops with higher income stability. In drought scenario, due to reduced water volume, the cropping pattern tends to crops with less water requirements, and crops with higher income levels have less changes. Income risk, in the worst drought scenario (very severe drought) and climate change (scenario A2 during the period 2040-2049), would decrease by 68.1% and 6.377%, respectively. By reducing the income risk, the gross margin will be reduced. Considering the economic effects of climate change and drought in long-term, it is recommended to use drought and heat resistant varieties. Also, the area under cultivation of crops such as barley, corn, sugar beet, and tomato may be increased as they have a more stable income.

This study was carried out to investigate the effects of irrigation intervals and different planting dates on the yield and yield components of rice. A split-plot design based on randomized complete block design was used with three replications, at Rice Research Institute of Iran (Rasht) in 2016 and 2017. The main factor was irrigation at four levels (full flooding, 5, 10 and 15 days irrigation intervals) and the secondary factor was planting date at three levels (April 21, May 11, and May 31). The results of analysis of variance showed that irrigation and planting date had a significant effect on the yield of rice at 1% probability level. The highest amount of biological yield was obtained in full flooding and 5-day irrigation interval, with an average of 10960 and 10238 kg/ha, respectively, and in May 11 and April 21 planting dates with an average of 10553 and 10397 kg/ha, respectively. The highest 100-grain weight was obtained in May 11 and May 31 planting dates, the maximum number of panicle per plant was observed in full flooding treatment, and in May 11 planting date and the highest number of filled grains was observed in full flooding treatment. The maximum number of hollow grains was observed in 15 and 10-day irrigation intervals and May 31 planting date. The results showed that the full flooding irrigation with a yield of 4271 kg/ha had the highest grain yield. The 10 and 15 days irrigation intervals had less grain yield than flood treatment and  5-day irrigation interval treatments. In two years of the experiment, the planting date of May 11 had the highest grain yield with an average of 3820 kg/ha. In this experiment, the May 11 planting date had the most favorable environmental conditions for growth and had a good yield-stability.

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.

Presently, the country has a problem of water scarcity, therefore, development of alternative approaches with operational capabilities can be considered as a matter of utmost importance. In this study, using comparative advantage indexes (i.e. domestic resource cost (DRC), social cost benefit ratio (SCB) and net social profit (NSP)), the ranking of crops and adaptation of products with limited water resources and current cropping pattern with comparative advantage patterns in the district of Kashmar were studied. Then, by analyzing the cost of consuming water input at the rate of 15%, 35% and 60%, the sensitivity analysis of this input was analyzed. Agricultural and trade data were collected from the Ministry of Agriculture Jihad and the Customs, respectively, in the years 2016-2017. After determining the optimal values of the indices, the results showed that saffron and grapes had comparative advantage with both free market and official exchange rates, while wheat and barley had a comparative advantage only in the official exchange rate. Also, the sensitivity analysis of water input showed that comparative advantage and product ranking varied in the three different scenarios (15%, 35% and 60%). Finally in order to adapt the comparative advantages of the products with the region's conditions, enhancement of support and implementation of suitable research and promotion plans were suggested.

The wetted profile pattern is an important factor to consider when designing and managing a surface and subsurface drip irrigation systems. The knowledge of the pattern dimensions is imperative in choosing the suitable spacing between emitters and the correct distance between laterals. The experiments were carried out in a transparent plexiglass tank (0.5 *1.22 *3 m) using three different soil textures (sandy clay, sand clay loam, and sandy loam). The drippers were installed at 3 different soil depths (15, 30 and 45 cm). The emitter outflows were 2.4, 4 and 6 Lhr-1 with irrigation duration of 6 hr. In this study, using the data obtained from the laboratory experiments and conducting the nonlinear regression analysis using Microsoft Excel Solver tool 2010, an empirical model was developed to predict the horizontal distribution of the wetting front for different application times. The suggested model includes estimation of the wetted radius at the top and bottom of the emitter horizontal axis as a function of emitter discharge, saturated hydraulic conductivity, water application time, soil bulk density, emitter installation depth, initial soil moisture content, and the percentages of sand, silt, and clay in the soil. We pursued a similar procedure in developing empirical formulas for estimating the wetted radius at different soil depths (by optimizing the coefficients of Equations) to predict the full shape of the wetting pattern. The best performance of the model was related to the depth of zero (on the emitter positioning axis), where the values of RMSE, MAE,  and R2 were 2.15, 1.7 cm, 14.85 % and 0.92, respectively. The lowest performance of the model was related to the depth of 20 cm from the emitter, where values of  RMSE, MAE,  and R2 were 3.93, 3.26 cm, 37.55% and 0.75, respectively (R2 coefficient was significant at 5% level). The results of this research showed that the suggested model predicted the full shape of wetting pattern with acceptable accuracy. Considering these models in designing subsurface drip irrigation systems could improve system performance.