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Background and Objectives A large part of Iran is located in arid and semi-arid climates. Despite the existing shortcomings, agricultural in Iran is highly dependent on applied irrigation water. Water is considered as the most important and limiting input of agricultural production in Iran (Zibai, 2007). Rapeseed (Brassica napus L.) is the third annual oil crop in the world after palm oil and soybeans, which is cultivated for its edible oil and is easily replaced by cereals (Anonymous, 2013). The main goal for improving agricultural water productivity in the world is to increase agricultural products with less water consumption, thus reducing the share of water in the agricultural sector and allocating more water to other uses and, most importantly, the water needs of the environment (Heydari, 2014). So far, no report has been presented on the evaluation of different irrigation systems in rapeseed cultivation in East Khuzestan. The main purpose of this article was to measure irrigation water of rapeseed in Behbahan city and compare their physical and economic water productivity. In this way, the physical and economic productivity of water under different agricultural management and in irrigation systems can be compared and evaluated. Methodology This project was implemented in the field to determine canola irrigation water demand under the management of farmers in Behbahan city. In 26 farms, the volume of canola irrigation water (without interfering with their irrigation program) was measured. To determine the volume of irrigation water, the amount of inflow from the selected water source was measured with a suitable device (WSC flume, meter or ultrasonic flow meter). Linear multivariate regression analysis was used to investigate the effects of the independent variable on the above dependent parameters. Water requirement was calculated based on the FAO Penman-Monteith model using the daily statistics of Behbahan Synoptic Meteorological Station (minimum and maximum daily temperature, minimum and maximum daily humidity, wind speed and maximum sunny hours) and using ETCalculator software. One-way analysis of variance was used to show a statistically significant difference between the means of two or more independent groups. To compare physical and economic productivity indices of irrigation water, there was a need to resolve the difference. Therefore, the standard Z-Score standardization method was used to resolve the scale difference. SPSS16 software was used for statistical analysis. Findings The average irrigation water productivity in 26 farms ranged from 0.351 to 1.545 kg per cubic meter and economic water productivity ranged from 6940 to 3719660 Rials per cubic meter. Irrigation water volume with t-statistic (-11.193) and equivalent beta coefficient (-0.056) had a significant negative effect at the level of 1% on the irrigation water productivity and a significant negative effect at level 5% had on the economic water productivity. The method of irrigation of selected farms (surface or sprinkler) had a significant effect at the level of 5% on the physical and economic irrigation water productivity. The calculated scores according to Z-Score showed that 31% of the farms that had sprinkler irrigation system were in good condition in terms of physical and economic productivity of irrigation water and none of the farms in the surface irrigation system were ranked well in terms of irrigation water productivity, but 8% of the irrigation farms had good economic productivity. The results of Pearson correlation coefficient showed that rapeseed yield had a positive and significant correlation at the level of 1% and 0.608 with irrigation water productivity, while yield had no significant correlation with economic water productivity. Conclusion Comparison of the results of average traits showed that the implementation of sprinkler irrigation system in the studied farms has increased the physical and economic productivity of irrigation water. The high cost of implementing the sprinkler irrigation system in agricultural lands has not caused these farms to have lower physical and economic productivity than surface irrigation farms, instead the cost of implementing the irrigation system during ten years of using this system has led to better management use of irrigation water, increase the physical and economic productivity of irrigation water. This management is mainly implemented by irrigation and drainage companies by shortening the irrigation period and increasing irrigation times. Prevents grain filling and by adjusting the irrigation hour at each irrigation time by moving the sprinklers by irrigation workers, prevents water wastage and deep percolation of water from the root zone and compared to surface irrigation from water losses prevents the end of irrigation furrows. This management, along with reducing labor costs while keeping the canola crop, has reduced costs and increased the physical and economic productivity of irrigation water. [ABSTRACT FROM AUTHOR]

Knowledge of the sensitivity of various soil hydraulic properties is beneficial for model development and application purposes. It can lead to better estimated values, better understanding, and thus reduced uncertainty. In the present study, an extensive sensitivity analysis was performed to investigate the effects that various soil hydraulic properties have on subsurface water flow below furrows during two successive irrigation events to see which irrigation event was more sensitive and to analyze the effect of spatial variations in the initial soil water contents within the soil profile. Testing the sensitivity of the various soil hydraulic parameters in the van Genuchten-Mualem expression was carried out using the HYDRUS-2D model for two irrigation events 10 days apart. Results showed that the first irrigation event was clearly more sensitive than the second one. The latter event was mainly associated with the nonuniformity of the initial soil water contents within the soil profile. Pressure heads in the soil profile were more sensitive than cumulative outlet fluxes and soil water contents. Sensitivity analysis results for pressure heads, cumulative fluxes, and water contents indicated that in every case the most sensitive parameter was the hydraulic property shape factor (n) followed by the saturated water content ([[theta].sub.s]), the saturated hydraulic conductivity ([K.sub.s]), the residual water content ([[theta].sub.r]), and the shape factor in the soil water retention curve ([alpha]), with the pore-connectivity parameter (l) the least sensitive parameter during both irrigation events. Pressure head sensitivity analysis for all parameters studied showed that the least sensitivity was linked with the wetting front as it gradually moved deeper with time, and the highest sensitivity was observed in those regions where the initial soil water contents were lower. Similarly, for water contents, higher sensitivity occurred in the drier regions during the first irrigation event and near the moisture front in the second irrigation event. Both pressure heads and water contents showed some sensitivity near the soil surface during both irrigation events, suggesting the importance of evaporation from the soil surface. CE Database subject headings: Furrow irrigation; Sensitivity analysis; Soil properties; Hydraulic properties; Subsurface flow.

Because of field-scale heterogeneity in soil hydraulic and solute transport properties, relatively large-scale experiments are now increasingly believed to be critical to better understand and predict the movement of water and dissolved solutes under field conditions. In this study, five field experiments were conducted on short blocked-end furrows to assess the effects of irrigation water level on water flow and solute transport in furrows. Three experiments were carried out, each of the same duration but with different amounts of water and solutes resulting from 6, 10, and 14 cm furrow water depths, designated as low, moderate, and high water levels, respectively. Two more experiments were performed with the same amounts of applied water and solute and, consequently, different durations, on furrows with depths of 6 and 10 cm of water. Results show that both the water level and the duration play an important role in transporting and distributing water and solutes in the soil profile. A positive correlation was found between water level and infiltrated amount of water or solute. Irrigation/solute application amounts increased with decreasing water level. Water and solutes were both distributed almost vertically (one-dimensionally) for the low water level and short application treatments, while they moved much more two-dimensionally with low and moderate water depths but longer application times. Irrigation with the 14 cm water level and short application time improved the distribution of water and solutes within the soil profiles, while also causing relatively less deep percolation of water and solutes as compared to low and moderate water levels and relatively long duration times. CE Database subject headings: Furrow irrigation; Water levels; Solutes; Water quality; Water depth; Data analysis; Transport phenomena.

In this study, a zero-inertia model (ZIMOD) is presented to simulate all phases of border and furrow irrigation systems. The governing equations were discretized using a control volume of moving cells, by procedures reported in the literature for borders and for furrows. Later, the discretized equations were linearized by applying a Taylor series expansion according to the Newton-Raphson procedure, and then the algebraic linearized equations were iteratively solved using the Gaussian elimination technique. The ZIMOD was verified against several field experimental data and output of various numerical models in the SIRMOD package. Computational times, errors in predicting advance and recession trajectories, and estimated runoff and infiltrated volumes were compared. All models used in the comparative analysis predicted the advance and recession times and the infiltrated and runoff volumes satisfactory. However, models in the SIRMOD package were computationally faster than ZIMOD. DOI: 10.1061/(ASCE)0733-9437(2003)129:3(208) CE Database subject headings: Border irrigation; Numerical models; Furrow irrigation.

The application of plant nutrients with irrigation water is an efficient and cost-effective method for fertilizer application to enhance crop production and reduce or eliminate potential environmental problems related to conventional application methods. In this study, a combined overland water flow and solute transport model for analysis and management of surface fertigation/chemigation is presented. Water flow is predicted with the well-known Saint-Venant's equations using a control volume of moving cells, while solute transport is modeled with the advection-dispersion equation. The 1D transport equation was solved using a Crank-Nicholson finite-difference scheme. Four, large-scale, field experiments were conducted on blocked-end and free draining furrows to calibrate and verify the proposed model. The results showed that application of solute during the entire irrigation event, or during the second half of the irrigation for blocked end conditions with appropriate inflow rates, produced higher solute uniformity than application of solute during the first half of the irrigation event. Measured fertilizer distribution uniformity of the low quarter ranged from 21 to 76% while fertilizer distribution uniformity of the low half values varied between 62 to 87%. The model was subsequently applied to the experimental data; results showed good agreement with all field data. Water balance errors for the different experiments varied from 0.004 to 1.8%, whereas fertilizer mass balance errors ranged from 1.2 to 3.6%. A sensitivity analysis was also performed to assess the effects of longitudinal dispersivity parameter on overland solute concentrations. A value of 10 cm for dispersivity provided a reasonable fit to the experimental data. DOI: 10.1061/(ASCE)0733-9437(2003)129:2(71) CE Database subject headings: Overland flow; Furrow irrigation; Dispersion; Fertilization; Data analysis.