Journal of Water Research in Agriculture
Year:2016 | Volume:29 | Issue:4|Papers Count:11

Intermittent irrigation is a method to increase water productivity of rice (Oryza sativa L.). In this study, the effects of this type of irrigation combined with two periods of midseason drainage on growth parameters of two rice cultivars were investigated in subsurface drained paddy fields. The experiment was laid out as split plot in a randomized complete block design with three replications during 2014 growing season. The main factor consisted of drainage systems in the study field including three conventional subsurface drainage systems with drain depths and spacing of, respectively, 0.9 m and 30 m (D0.9L30), 0.65 m and 30 m (D0.65L30), and 0.65 m and 15 m (D0.65L15). In addition, 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 (bilevel), and a treatment without subsurface drainage (control) were included in the study. Sub-factors including rice cultivars Hashemi and Daylamani Tarom were planted in the study area. Midseason drainage was conducted in two periods of 10- day (25 to 34 days after transplanting) and 5-day (43 to 47 days after transplanting). During the growing season, sampling was done to determine leaf area index (LAI), total shoot dry weight (TDW), crop growth rate (CGR), relative growth rate (RGR), leaf area ratio (LAR) and net assimilation rate (NAR). Conducting such water management through subsurface drainage systems increased most of the studied parameters of Hashemi cultivar so that significant differences were found between CGR, NAR, and RGR of D0.9L30 and the control treatment. Maximum dry weights of Hashemei and Daylamani cultivars were 858.8 and 1006.6 g m-2 related to D0.65L15 treatment and maximum leaf area indexes of these cultivars were 4.87 and 5.43 related to bilevel and control treatments, respectively. However, there were not significant differences among different treatments for each cultivar. Based on the results, two periods of midseason drainage through subsurface drainage would improve rice growth characteristics if proper drainage time is selected.

In order to study the effect of limited irrigation on increasing the yield and water productivity of soybean, a split plot experiment based on a randomized complete block design with four replications was conducted in two cropping seasons of 2013 and 2014, in Rasht. Three irrigation treatments including two irrigations (I2): irrigation at flowering and pod formation stages, three irrigations (I3): irrigation at flowering, pod formation and ripening stages, and rainfed (I0): as control treatment were allocated to the main plots and three soybean genotypes including Williams (V1), L17 (V2), and Habbit (V3) to subplots. During the critical growth stages of the plant, based on the irrigation treatment and considering the precipitation and available moisture in the root zone, only one irrigation was applied (I1) in 2013 while Williams and Habbit genotypes were, respectively, at pod formation and at flowering stage. But, in 2014 crop season, considering the lower precipitation, all irrigation treatments were conducted. Yield and yield components were measured at seed ripening time. The results showed that the limited irrigation in both years improved yield and yield components of all soybeans genotypes. The highest average grain yield in both crop seasons were obtained with I1V2 and I3V2 treatments, being 4616 and 4198 kg/ha, respectively. In both cropping seasons of 2013 and 2014, L17 genotype had the highest average grain yield compared with the other two genotypes, being 3932 and 3000 kg/ha, respectively, therefore, it can be recommended for planting in Rasht region. In 2013 and 2014 crop seasons, respectively, I1V2 and I3V2 treatments had the highest water productivity, corresponding to 1.72 and 0.97 kg/m3.

Almost all districts of the country are experiencing quantitative and qualitative decline of agricultural water resources. Considering the extensive expansion of greenhouse cultivation and importance of tomato production, and in order to evaluate the combined effect of salinity and drought stress on growth and yield of tomato plant (Lycopersiconesculentum Mill. Cv. Oriental), four levels of irrigation (125% ETc, 100% ETc, 75% ETc and 50% ETc) and six levels of salinity (0.1, 1.3, 3, 5, 7 and 9 dS/m) were factorially combined in a completely randomized design with 3 replication in a greenhouse soilless culture. Yield and its indexes were measured during the crop growing season. As expected, results indicated that salinity of the nutrient solution and drought stress had significant negative effects on yield and growth indexes of plant. Yield data were fitted on different production functions (simple linear, logarithmic linear, quadratic, and transcendental). The results indicated that the simple linear form was the optimum form. The S1W4 treatment (EC=0.1 dS/m, and 50% ETc) with 34.6 kg/m3 and S5W1 treatment (EC=7 dS/m, and 125% ETc) with 6.4 kg/m3 had the highest and lowest water use efficiency, respectively. The iso-yield curves showed that by increasing irrigation water amounts, water with higher salinity can be applied without changing the yield.

Water deficit is not avoidable under arid and semiarid regions. But, the adverse effects of water deficit can be reduced by recognition of the impact processes and application of suitable chemical fertilizers. Nitrogen requirement varies under different irrigation managements and its proper usage can prevent drastic reduction of yield under the abovementioned conditions. This study was conducted for evaluating the combined effects of nitrogen and irrigation on the yield and quality of the local cultivar of garlic (Allium sativum 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 four levels (0, 50, 100 and 150 kg N per ha) using three replications and line source sprinkler irrigation system. The total irrigation water was measured by catch cans that were fixed in the middle of each plot. The results showed that the application of nitrogen significantly increased yield, tuber and leaf nitrogen concentration of garlic, and decreased mean cloves weight. The water deficit decreased yield, mean cloves weight and leaf nitrogen concentration of garlic and increased number of sheaths on bulbs and water use efficiency. The interaction of nitrogen and irrigation was not significant on the measured attributes. The highest amount of garlic yield was obtained by using 409 mm irrigation and 100 kg N per ha.

To study the effects of using plastic mulch on soil moisture and salinity changes under drip irrigation system in mature pistachio trees (Ohadi cultivar), a research was conducted in a randomized complete block design in two orchards with different treatments in terms of water consumption (4100 and 6170 m3/ha), irrigation frequency (8 and 12 days), and trees growth. The study was carried out in the western suburbs of Rafsanjan, Iran. In each of the orchards, three mulch treatments including: without mulch (treatment C), black-and-white plastic mulch (treatments MB, MW), with three replications were used. At the end of the season, data on growth characteristics, quality and quantity of the product, and water use productivity (WUP), were averaged and compared using Duncan multiple range test to determine the effects of using plastic mulch on these traits. The results showed significant effect of plastic mulch on all growth factors, quantity and quality of yield, and water use productivity. Moreover, in most cases, the color of mulch did not affect these traits. Overall, using plastic mulch in orchard 1 increased the dry product up to 271 g per tree, reduced blanking to 10.6 percent, increased splitting by 11.2 percent, reduced the number of grains per ounce of pistachios by 2.3 units, and increased the water use productivity by 100 percent compared to the control. Also, in orchard 2, plastic mulch increased the dry product up to 1090 g per tree and increased the water use productivity by 36 percent compared to the control. Measurement of soil moisture changes in between two consecutive irrigations indicated significant effect of mulching on conserving soil moisture in comparison with the control. Considering the Permanent Wilting Point (PWP) and Readily Available Water (RAW) of the experimental soils, proper irrigation frequency for pistachio trees in uncovered loamy sand to sandy loam soils under drip irrigation is 5 to 9 days, and in the use of plastic mulch, it is 11 to 15 days.

The effect of soil matric potential on yield and growth parameters of three varieties of cucumber in greenhouse was carried out during 2012 and 2013 growing seasons in Jiroft area. The treatments were laid out in randomized complete block design with three replications. The treatments were comprised of three soil matric potentials of 45, 60, and 75 centi-bar for initiation of irrigation in the main plot and sub plot consisted of three cucumber varieties (Negin, Hilarious and Dominos). The results showed that water use in treatments 45, 60, and 75 centi-bar tensions was, respectively, 6300, 5100, and 3900 m3 ha-1, which was 18% less than irrigation based on Class A pan evaporation.. Fruit yield, LAI, plant height, and fruit diameter decreased 2.7%, 2%, 2%, 0.73% and 2.3 percent, respectively, but water use efficiency increased 22 percent. On the other hand, yield in Dominos variety compared to Negin and Hilarious increased 6.2% and 6.4 percent, respectively, and water use efficiency increased 13.2% and 13.7 percent, respectively. According to the results, planting Dominos variety and 60 centi-bar soil matric potential for irrigation initiation is recommended to achieve the highest water use efficiency.

Various mathematical models are available for estimating the response of plants to combined drought and salinity stress and the share of each component in water uptake. The reduction functions are classified as additive, multiplicative, and conceptual models. In this study, 5 different macroscopic reduction functions, namely, Van Genuchten (additive and multiplicative), Dirksen et al., Van Dam et al, and Homaee, were evaluated in greenhouse conditions using pepper data. This experiment was performed based on a completely randomized design with 3 replicates and 3 levels of salinity (2.5, 4.5, and 6.5 dS/m). Drought levels were carried out as matric potential during the experiment at 3 levels (50%, 60%, and 70% of field capacity). The results of this study indicated that the crop response to drought and salinity stress was additive at low salinity level (2.5 dS/m) and multiplicative at 4.5 and 6.5 dS/m salinity levels. Also, reduction function of Van Genuchten (average RMSE=3%, ME=0.15) had the best fit at low salinity level (2.5 dS/m). Among the multiplicative models, reduction functions of Dirksen model at 4.5 dS/m with average RMSE=5% and ME=0.09 was in better fit to the measured data than the other functions. Homaee (average RMSE=9%, ME=0.12) and Vandam models (average RMSE=9%, ME=0.11) at higher salinity level (6.5 ds/m) were in better fit to the measured data than the other functions.

Distribution uniformity of water is one of the most important parameters for evaluation of irrigation systems. Numerous equations have been developed to calculate distribution uniformity coefficient in sprinkler irrigation systems. The provided equations do not necessarily yield the same results in calculation of uniformity coefficient for one specific farm in a particular condition. The aims of this study were the evaluation of various equations proposed by different researchers, investigation of the effects of different field conditions on the results, investigation of the existing relationships among outcomes of the equations, and feasibility of using these equations. For this purpose, distribution uniformity coefficients were calculated using the equations presented by Christiansen, Hawaiian Cane Society Specialists Hart and Reynolds, Wilcox and Swailes, Karmeli, Criddle et al, Benami and Hore, and Beale and Howell, for 10 sprinkler irrigation systems in Shahrekord fields. Data analysis was performed using Statistical Analysis System (SAS) Software in a randomized complete block design. The results indicated that there were significant differences (P<0.05) between the aforesaid coefficients and some of these equations estimated a negative number or a number larger than 100% for coefficient of uniformity in some specific conditions of sprinkler irrigation. Furthermore, in all cases, beta distribution could estimate the water distribution uniformity coefficient (CU) better than the normal and uniform distributions. In all three beta, normal, and uniform distributions, minimum agreement between predicted and measured values was related to equations by Karmeli, Beall and Howell, and Benami and Hore; and the most agreement, particularly in the beta and normal distribution, was related to the Christiansen equation. The results conclusively indicated that a number of coefficients of uniformity such as Benami and Hore, Karmeli, and, to some extent, Beal and Howell coefficients are strongly dependent on specific field conditions and are not applicable under other field conditions.

Reduction of water losses due to increase in the application uniformity in sprinkler irrigation systems needs appropriate selection of the sprinklers spacing and arrangement. In the present study, to evaluate the impact of spacing and arrangement of sprinklers on uniformity coefficient (UC) of the irrigation system and to investigate the qualitative and quantitative changes of UC due to changes in the parameters of the area covered by the sprinkler and wind speed, the test of distribution pattern of a single sprinkler was performed. The test was conducted according to ISO 8026, ASAE S398.1and ISO 7749, 2 standards on three VYR 35, IRILINE 30, and RAINBIRD 40B sprinklers. In this study, the square shaped arrangement had the highest UC and lowest sensitivity to decreasing coefficient of uniformity with an average of 5.3% and 5.5 percent for the average increasing of 59.4% and 98.3 percent in the covered area and wind speed, respectively. The least sensitivity of the UC were obtained for the IRILINE sprinkler with the mean reduction values of 3.4% and 5.48 percent for the average increasing of 37% and 117.8 percent in the covered area and wind speed, respectively. Results showed that to achieve the desired coefficient of uniformity, the maximum sprinkler spacing should be considered as 40 percent of the nominal application diameter of the sprinkler with a square arrangement when wind speed exceeds 4 meters per second.

In economics, each resource that is scarcer should have a more accurate pricing mechanism. Water is one of the most valuable natural resources and, as one of the main inputs for production of agricultural products, has a special place in sustainable development of agricultural sector. Determination of economic value of water in Zanjanrud river basin significantly helps to promote water use efficiency and saving of water users and demand management. By means of production function for onion and colleting questionnaire from 99 onion farmers in this region in 2012-13, we evaluated the economic value of water. Production inputs including cultivation area, irrigation, chemical fertilizer, pesticide, manpower and also pressurized irrigation method were the imaginary variables. After estimation of the flexible trans-log, generalized second order functions and generalized Leontief and according to the criteria and econometric tests, the quadratic generalized function was recognized as the best production function. The results from the analysis of the data showed that the economic value of water in cubic meters per kilogram of onion production was 1707 Rials. This exchange value of water was higher than the exchange value of water at peak demand, which was 705 Rials. Therefore, in Zanjanrood river basin, the economic value of water was more than the exchange value of water.

Climate change affects precipitation and temperature patterns and, hence, may affect the crops yield. In this study investigated the simulation of grain yield and biomass of soybean under future climate in different irrigation treatments and different planting date as adaptation strategy using Aqua Crop model. For this purpose, the data of precipitation, minimum temperature, maximum temperature and sunshine hours and the LARS-WG statistical downscaling model was used from HadCM3 atmospheric general circulation model and under emission scenarios A2 and B1, in the periods 2011- 2038, 2039-2066 and 2067-2094. Aqua Crop model was calibrated and validated by the data collected in the field before being used. Finally, the amount of grain yield and biomass simulated in future periods, for 6 different planting dates and for treatments of 100%, 75% and 55% water requirement. Based on the results, under emission scenarios A2 and B1 in 17 June for the period 2011- 2038 as compared to the base period (1981-2008), the amount of simulated biomass and grain yield, decreased, respectively, between 5 to 11.5% and 8.3 to 13.7% and for the period 2039-2066 increased, respectively, between 18.6 to 24% and 16 to 24.4%, and for the period 2067-2094 increased between 9 to 21.8% and 7.2 to 21.2%. Also, by selecting planting date of 20 June, the largest increase of biomass and grain yield were simulated for periods 2011-2038, 2039-2066, and 2067-2094 under the A2 and B1 scenarios. These results will be useful for future irrigation planning in Gorgan area.