مجله مدیریت آب و آبیاری
سال یکم شماره 1 (بهار 1390)

Controlled drainage is one of the strategies to reduce negative environmental effects in conventional drainage systems. This study examines the effect of controlled drainage on quality and quantity of drainage water, specifically amounts of salt and nitrate in drainage water, and nitrate uptake by maize (SC 704) with sandy loam soil texture in Karaj. The experiment was performed as a randomized complete design including three treatments with three replications: free drainage (FD) and controlled drainage with 40 cm (CD40) and 60 cm (CD60) controlled water tables. Irrigation intervals were based on MAD = 0.65 in FD treatment. For all treatments, irrigation depths were determined based on deficiency of soil moisture from field capacity with 70 percent application efficiency. According to the research hypothesis, irrigation losses cause rising water table during the season, but the results showed that 30 percent irrigation losses during implementation in CD treatments did not raise the water table to the expected control levels due to increased consumption of plant. So between two water table control treatments, there was no significant difference. In FD treatment, which drainage water discharge was facilitated, both plant water consumption and yield were reduced. Effect of water table management was significant (p< 0.01) on nitrate and salt balance. Volume of drainage water in FD treatment was 34.8 percent of total gross irrigation whereas in CD treatments no drainage water was produced. In FD treatment, due to appropriate leaching conditions, salt and nitrate levels in drainage water was 63 and 20.8 percent of amount of input salt and nitrate, respectively. While in CD treatments due to controlled conditions, salt and nitrate leaching was not observed. At the end of cultivation period, measured values showed that nitrate accumulation in soil profile were greater in FD treatment than CD treatments. This observation shows that under CD treatments, as compared with FD treatment, plant nitrogen absorption is increased which is reflected by higher crop production. At the end of the growing season, however due to lack of leaching in CD treatments, a higher salt accumulation is observed in soil profile but this can be managed with leaching of salts during the off- season periods.

Water productivity is a function of crop yield and management operation. Determination of different yield levels through field experiments is difficult. Therefore, applying simulation model is an approach which makes possible to assess water balance, simulate growth process and survey different scenarios. Using the CropSyst crop growth model to analyze water productivity, as an indicator of water use efficiency (WUE) at the basin scale, and evaluation of management scenarios in Karkheh basin in west of Iran was studied. The vast range of WUE (0.27-0.45) in this region shows that less water expenditure is able to increase agricultural products. Results of model study showed that achieving of soil initial moisture to field capacity about 19.6%, leave total crop residues, early rainfall and sowing date in comparison with conventional conditions, and seed density (300 seeds/m2) are effective to increase water productivity and yield.

Accurate estimation of reference evapotranspiration plays a key role in water resources management and irrigation scheduling. The FAO Penman-Monteith (F-P-M) is a reference method for calculation of evapotranspiration that needs temperature, humidity, wind speed and solar radiation. In many stations, it is not an easy task to measure the whole weather variables. Thus, in this situation, one must use some of the equations that require less climatic data. ANNs are an effective tools to model nonlinear phenomena with an interaction relationship. In this study, Seven ANNs with different input combinations have been implemented and compared with ten locally calibrated empirical and semi-empirical ETo equations (with estimated solar radiation and humidity parameters as inputs) in Gorgan synoptic station. The comparisons have been based on the basis of statistical error techniques, using F-P-M daily ETo values as a reference. ANNs have obtained better results than the locally calibrated ETo equations in the three groups: temperature and/or relative humidity based methods ANN 3model and HS equation with RMSE equal to 0.422 and 0.551mm d-1, respectively; solar radiation-based methods ANN 4 model and T equation with RMSE equal to 0.372 and 0.518 mm d-1, respectively and methods based on similar requirements to those of PM56 except for the estimation of solar radiation and/ or relative humidity ANN 6 and F-P-MRHest equation with RMSE equal to 0.208 and 0.310 mm d-1, respectively.

Saturated hydraulic conductivity (Ks) is one of the most important physical features of soil that have wide usage in soil and water science. Measuring Ks carries on laboratory and field. Guelph permeameter (GP) method is one of the field measuring method for determining field saturated hydraulic conductivity (Kfs) above the ground water table. Well-shape-factor (C) is one important parameter needed to calculate Kfs, which related to pressure gradient of flow through the soil around the borehole. Several approximated analytical solution are presented to determine C, such as Porchet solution, Glover solution, half-source (Reynolds et. al.) solution. Numerical solution is obtained using finite difference by Reynolds et. al. (1985) and applied formulae fitted them by Zhang et. al. (1998). Developed theory of flow out a borehole corresponds the flow to hydraulic conductivity (Kfs) and soil matrix potential (Ǿm) which can be obtained by measuring outflow in two different ponding depth in single hole. One of the restrictions of this method is the negative results that may be seen in some cases. In this research, the GP experiments were down in 18 holes of 3 cm radius and 60 cm depth in a loamy soil with different ponding head (H), (maximum and minimum H was 5 and 20 cm, respectively). Then the field saturated hydraulic conductivity (Kfs) was determined by two head analysis of GP, Richards, Laplace and Regression analysis with different solution methods for well shape factor (C). Results showed that if the Porchet method was used for C factor calculation, negative results have been minimized and other methods for the C calculation (Glover, Numerical and Half-Source) have been produced low to high negative results for (Kfs), respectivity. According to this study, the increasing of ratio of H2 to H1 will be caused a large number of (Kfs) values to be positive and also there were no significant differences between their means. In the Richards, Laplace and Regression analyses, the Glover, Numerical and Half-Source solution of C had the least deviation of mean, respectively. Analyses of Regression model with Numerical Solution of C has the nearest results with two head analysis.

According to the irrigation systems design standards, allowed pressure variation in lateral pipes is 20 percent. Reasons for this rate selection, which since the 60's is performed, are not known. The increased changes in allowed pressure tubes to lateral pipes design, the increased sprinkling system required pressure and the increased nonuniform sprinkler distribution, so energy supply costs and water loss will be increased. On the other hand, designed lateral pipes with lower allowed pressure variation, cause better irrigation uniformity, and decreased system required pressure, but costs of tubes per area unit will be increased. The aim of this study is investigation of allowed pressure variation effect along lateral pipes of hand move sprinkler irrigation system on purchase costs of pipes, energy supply and water economic costs. In this experiment, we designed sample farm hand move sprinkler irrigation system with allowed pressure variation 5, 10, 15, 20, 25 and 30 percent for alfalfa culture in Khuzestan, and based on these designing and economic value per cubic meter of water in this region, investment cost, current and total cost were estimated. The results showed that by calculating water supply cost, the highest cost is related to fields with pressure variation of 30 percent, and the lowest cost and water price is related to fields with pressure variation of 15 percent, and several economic values of water in Khuzestan, have no effect on the best economic selection of pressure changing ranges. Changes in pressure above 20 percent, losses and costs are high and the pressure change of 15 percent in lateral pipes is a good option to design the hand move sprinkler irrigation system in Khouzestan.

Shortage of water is one the main factors limiting the development of agricultural activities and farmer participation is critical to improve on-farm water management and crop productivity. This research was done with aim to identify impeding and facilitating factors influencing on using new irrigation methods by farmers in west Boshroyeh Township in Southern Khorasan. The methodological approach was a descriptive-correlational study of survey type. The statistical population of the study was consisted 100 farmers in West villages of Boshroyeh Township. Using stratified sampling method, 80 farmers were chosen. Information was gathered through a questionnaire and its face validity was confirmed by faculty members and experts of agricultural extension and irrigation. The reliability analysis was conducted with completing 30 questionnaires and Cronbach’s alpha coefficient for main parts of questionnaire was 0.75 and 0.72, respectively. Data were analyzed using SPSS software. The results showed that there are significant relationships between amount of farmers´ ovation from new methods of irrigation (95%), type of operations for attracting farmers participation (99%), farmers opinion about threat of their future agriculture affected by water shortage (95%), importance of using new irrigation methods for agriculture (99%) and number of farmers´ meeting with extension worker every month (99%) and impeding and facilitating factors influencing on using new irrigation methods. This study has recommended performance of extension education class and facilitates farmers using loan for setting up new irrigation methods.

Soil moisture retention curve is one of the soil hydraulic prosperities which its direct measurement is time consuming and expensive. Therefore, indirect methods such as developing pedotransfer functions have been used to predict this characteristic from soil readily available or easily measurable data. In this study, multiple linear regression method was used to develop point pedotransfer functions (PTFs) for saline and saline-alkali soils of Iran. For this purpose, 68 soil samples with EC values greater than 4 dS/m of which more than half of them had ESP values greater than 15% were selected. Using Cross validation method, the random splitting of data into the development and validation subsets was repeated 10 times. A ratio of 3:1 was used to split data into development and validation sets in each replication. In the SPSS software, parameters such as geometric standard deviation (δg), geometric mean diameter (dg), sodium adsorption ratio (SAR), electrical conductivity (ECe), carbonate calcium (CaCO3), bulk density (BD), organic matter (OM), clay and sand content were applied as the independent variables, and volumetric water content was determined at matric potentials of 10, 33, 100, 300, 500, 1000, 1500 kPa. The derived PTFs were compared with the H3 model of Rosetta software for 10 splits of validation data set. Comparison of the mean RMSE and R2 values showed that the developed PTFs resulted in more accurate estimation than the Rosetta software at matric potentials of 100, 300, 500, 1000, 1500 kPa. Whereas, Rosetta model resulted in slightly better estimation than derived PTFs at matric potential of, 33 kPa. For the PTFs developed in this study, the RMSE, ME and R2 values ranged from 1.61 to 4.17 (cm3.cm-3), -0.181 to 0.66 and 0.52 to 0.76, respectively. While for the Rosetta model, RMSE, ME and R2 values ranged from 2.82 to 4.27 (cm3.cm-3), -2.65 to 0.094 and 0.37 to 0.74, respectively.