مجله پژوهش آب در کشاورزی
سال سی و یکم شماره 1 (بهار 1396)

In this research, the amount of maize yield was simulated under condition of different water salinities and climate change scenarios in Ahvaz region. Combined CSIRO-MK3.5 model and emission scenarios A1B, A2, and B1 were used as future (2021-2050 and 2070-2100) climate change scenarios (considering 1981-2010 as reference period). Additionally, AquaCrop model was used to predict the impact of climate change scenarios on maize yield under conditions of five salinity treatments including: (S0: Karoon river water (salinity: 2.3 dS/m); S1 (salinity: 3.5 dS/m), S2 (salinity: 4.5 dS/m); S3(salinity: 5.5 dS/m); and S4 (salinity: 6.5 dS /m). In order to show the impact of climate change alone, the amount of yield for each salinity treatment under different scenarios was compared with the same treatments yield under the reference scenario. Results showed that in the 2021-2050 period, the difference between maize yields for different scenarios was negligible compared to the reference scenario. However, in the 2070-2100 period, yield reduction under A1B scenario was %15, under B1 scenario 24%, and under A2 scenario, it was 35 percent. The results of salinity and climate change impacts together showed that, in the first future period, maximum reduction of yield would happen under the S4 B1N1 scenario (37 percent) and for the second future period, it would be under S4A2N2 scenario (58 percent). Finally, it was determined that the trend of yield reduction under salinity treatments was linear in all scenarios.

The main factor for managing and scheduling irrigation in dry area, is the plant response to drought stress. The majority of irrigation water in these areas contains soluble salts, therefore, salinity stress should be considered at the same time. Hence, this study was conducted in order to obtain the optimum depth of irrigation, considering drought and salinity stress individually and simultaneously, at three cutting times of forage sorghum in Sistan plain.This experiment used split plot in time in a factorial design with three levels of salinity (2, 5, and 8 dS.m-1) and four irrigation levels (50%, 75%, 100%, and 120% water requirement) at three cutting stages, with three replications. The depth of the water was determined for salinity levels and at various cuttings. In order to determine the separate and combined effects of salinity and irrigation water, the following criteria were used were used in each cutting: the index of final production compared to irrigation water depth (MPI), the final production compared to the salinity (MPECw), marginal rate of technical replacement for salinity and water (MRTSI, ECw ), the final output value of the irrigation water depth (VMPI), and the final output value of the salinity (VMPECw). MPI index showed that for each one centimeter increase in irrigation water depth, the first cutting had the least change in production(1.22 ton.ha-1) and the third cutting had the maximum amount (9.2 ton.ha-1). MPECw index showed that in the low salinity treatments, the second and third cuttings had, respectively, the lowest and the highest yield loss. MRTS index showed that in order for production to stay the same with one unit increase in salinity, the irrigation water depth must increase in the first, second, and third cuttings by, respectively, 5.86, 1.97 and 1.72 centimeter. Also, with increasing salinity levels in the all three cutting, optimum irrigation depth increased and in the all salinity levels, optimum irrigation depth in the first cutting was more than the second cutting, and in the second cutting it was more than the third cutting.

A field study was carried out to determine the effect of kochia (Kochia indica) planting density and water salinity on sorghum and kochia yield performance during 2012 and 2013. Treatments were irrigation water salinity levels (2, 6, 10 and 14 dS m-1) and kochia planting density of 0.0, 2.5, 3.3 and 5.0 plants m-2 on the sorghum rows. Results showed that sorghum dry matter (SDM) decreased as kochia density increased in all salinity levels. Salt tolerance threshold values for SDM were obtained at ECe 4.1 dS m-1. Each unit increase in ECe above this point reduced SDM by 10.5%. Contrary to the SDM, kochia dry matter was not affected by salinity levels in both years. Irrigation water salinity reduced height of sorghum and kochia in both years. Averaged over two years, leaf Na concentrations of kochia were 94.4, 86.6, 78.7, and 76.8 times more than that of sorghum at 2, 6, 10 and 14 dS m-1, respectively. Leaf Cl- concentrations of kochia were about 2.3, 2.4, 2.0 and 2.2 times higher than those obtained in sorghum under 2, 6, 10 and 14 dS m-1 salinity treatments in 2012, respectively. These values for 2013 were 3.6, 2.9, 2.5 and 1.9 times, respectively. Calcium concentration of kochia leaves at 2, 6, 10 and 14 dS m-1 were 2.9, 3.4, 2.4 and 2.7 times more than that of sorghum, respectively. In addition, kochia as a superior competitor could reduce yield of summer crops such as sorghum in saline conditions. It is recommended to cultivate the plant in marginal lands for forage production.

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) 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 was observed in Kerman region under surface irrigation. The maximum measured wheat CWPI and CWPI 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 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 秷�� rainfall) for optimum level of wheat CWP under deficit irrigation management were 300 and 420 mm, respectively.

Subsurface drainage is a prerequisite to growing winter crops and improving water management in rice season in the consolidated paddy fields in Northern Iran. Based on different cultivation condition, to decrease nutrient loss from subsurface drainage in these fields, adopting suitable strategies will decrease the pollution of water resources. A research was conducted in pilot farm of Sari Agricultural Sciences and Natural Resources University from May 2015 to April 2016 (during two successive rice-canola growing seasons) to evaluate the effect of subsurface drainage systems on nitrate loss and nitrate concentration in different soil depths. The subsurface drainage treatments were three existing subsurface drainage systems with mineral envelopes, including systems with 30-m spacing and 0.9 m depth, a drainage system with 30-m spacing and 0.65 m depth, a drainage system with 15-m spacing and 0.65 m depth, and a bi-level subsurface drainage system with drain spacing of 15 m and drain depths of 0.65 and 0.9 m as alternate depths (bi-level). The nitrate concentration was monitored in drainage water and at depths of 0.4, 0.9, 2 and 5 m during the study period. The results showed that the nitrate concentration and the total nitrate loss during rice growing season was 33-80% and 91-99 %, respectively, less than that in canola growing season. Also, the nitrate concentration in drainage water for drains with 0.9 m depth was more than that in drains with 0.65 m depth. On the other hand, nitrate concentration in surface depth was higher than lower depths in all treatments. Overall, in both seasons, drainage system with wider spacing and shallower depth drained out less nitrate than the other systems.

The present study was done for economic evaluation of pressurized irrigation systems in strawberry fields of Babolsar Township during a 4-year period from 2011 to 2015. To do this, at first, 282 farms (170 traditional and 112 pressurized irrigation systems) were selected using proportional stratified sampling. The data related to costs and revenues of the sample farms was gathered over four years with cooperation of Regional Agricultural Office and farmers. Then, collected data was analyzed by Net Present Value (NPV), Benefit- Cost Ratio (BCR) and Internal Return Rate (IRR) indices. The results showed that the sample farms produced strawberry economically under both traditional and pressurized systems. However, NPV and IRR were greater in pressurized irrigation system than the traditional one. Based on the results, IRR was calculated to be 48 percent in pressurized system while it was 38 percent in traditional one. In addition, BCR was calculated to be 1.48 and 1.37 in pressurized and traditional systems, respectively. So, considering national and regional drought crisis, development of pressurized irrigation systems is strongly recommended in the country and the region in order to conserve water resources.

Salinity is considered as one of the main problems affecting the growth and yield of many plants. Salinity tolerance varies with the amount of nitrogen uptake. The aim of the study was modeling the response of tomato (Solanum lycopersicum) under simultaneous salinity and nitrogen deficiency stresses. The indoor pot experiment was conducted in Damavand region, Iran, in 2015. The experiment was carried out on tomato plant in a factorial randomized complete block design with 3 replications. The treatments consisted of six levels of salinity (1, 2, 4, 6, 8 and 10 dS/m) and three levels of nitrogen including zero, 50 and 100 percent of the N-fertilizer needs. The maximum dry matter yield (25.8 gr) was obtained in the treatment with salinity of 1 dS/m and fertilizer consumption of 100%, while the minimum dry matter yield (5.8 gr) belonged to the treatment with salinity of 10 dS/m and no fertilizer application. Modified Liebig-Sprengel (LS) and Mitscherlich-Baule (MB) models were used to evaluate tomato response to nutrients. Comparison of statistics showed that for modeling tomato plants response to simultaneous salinity and nitrogen stresses, modified MB model (d=0.95) fitted better to the measured data compared to modified LS model (d=0.88). Therefore, modified MB model was recommended to estimate relative yield of tomato. Also, results showed that, at a fixed salinity level, by increasing amount of nitrogen application, the yield of dry matter was increased, while yield of dry matter decreased with increasing salinity. Threshold of yield decline in saline conditions is not fixed and depends on the amount of nitrogen in the soil. Decline of relative yield with increase in salinity wasn’t significant in zero-nitrogen treatment, which showed the influence of nitrogen deficiency relative to salinity. Therefore, threshold of tomato yield decline could be increased by nitrogen fertilizer management.

The main objective of the present study was determination of the economic value of irrigation water and simulation of the farmers’ behavior in response to reducing available water resources policy in Takestan Township, in Qazvin province. To achieve this goal, we used the positive mathematical programming (PMP) method and state wide agricultural production (SWAP) functions. First, the economic value of irrigation water in the studied township was determined. Then, framer's response to the scenarios of 5%, 10%, 20% and 30 percent reduction in available water resources was investigated. The required data belonged to crop year 2013-2014. To solve the presented experimental, software GAMS Version 24/1 was used. After solving the model, the economic value of irrigation water in Takestan Township was calculated at 1690 Rial. The results showed that there was huge difference between the economic value of irrigation water and water charge rates in this township. In addition, the results showed that with reduction in irrigation water availability in Qazvin, economic value of irrigation water increases and farmer's gross profit decreases. Finally, in order to avoid the indiscriminate use of water in agriculture sector, it is recommended to determine water charge for farmers of Takestan Township according to trend of changes in economic value and considering equity.

In this study, we investigated the source of agricultural water supply (qanat) and performance of agricultural crops in Mazreano village of Ardakan-Yazd. First, by using meteorological data and CROPWAT software, water requirement of horticultural products (pistachio and pomegranate) and field crops (wheat, barley, alfalfa and saffron) were determined in all months of the year. Then, volume of water in access of plants requirement and water deficiency in each month was calculated. Considering the water requirement of each crop relative to its economic benefit, we removed wheat, barley, and alfalfa in one scenario and assigned the water requirements of these plants to saffron cultivation. Then, the new cultivation area and the corresponding water demand were determined in each month. Considering the non-conformity of water demand and water availability in all months of the year, we proposed construction of water storage pool and calculated the net profit from the new plantings and compared it with the existing cultivation. The results showed that in this region change in cropping pattern is a proper solution for increased productivity and improving water consumption pattern. Changing the cropping pattern according to the proposed scenario could lead to three-fold economic net profit compared to the existing cropping pattern.

To evaluate the effect of irrigation intervals and different amounts of superabsorbent on the remobilization in sesame under Hamidieh region weather conditions, a field experiment was conducted a split plot in a randomized complete block design with four replications, in 2015. Treatments included irrigation intervals at 3 levels (60, 100 and 140 mm evaporation from class A pan) in the main plots and superabsorbent at three levels (0, 75 and 150 kg per hectare) in sub-plots. The results showed that the effect of irrigation intervals and superabsorbent could significantly increase the yield, the remobilization, current photosynthesis, and the contribution of remobilization to crop performance. The highest grain yield, remobilization, and current photosynthesis as well as the maximum contribution of remobilization and current photosynthesis was obtained in the treament consisting of 100 mm pan evaporation treatment and 150 kg per hectare superabsorbent. In examining the interaction between water and superabsorbent, highest grain yield (average 1216.46 kg per hectare) was in the treatment of 100 mm evaporation from pan and 150 kg per hectare superabsorbent. Considering the water shortage in the courty, it seems that the treatment including 100 mm pan evaporation and 150 kg per hectare superabsorbent not only can save water but can also make good economic performance.