JWSS - Journal of Water and Soil Science

Limitation of available water resources and crisis of water scarcity has been discussed in water conferences since a long time ago. In Iran’s climatic conditions, the most important problem for increasing agricultural production is limitation of available water resources. Drip irrigation methods are one of the suitable solutions for efficient use of water resources under a condition that selection, design, implementation and operation of drip irrigation systems would perform precisely. In this study, potential and suitability of drip irrigation systems in South Khorasan province was analyzed according to climatic conditions, quality of groundwater resources, topographical status and soil profile areas. To do this, all the effective parameters in drip irrigation are zonated and classified using software Arc GIS 9.3 and then using computational average method in AHP they are turned into a map to find suitable places for drip irrigation in the province. According to the study, about 50 percent of the land in South Khorasan province has the ability to use the drip irrigation system. The remaining 50 percent can also be used for drip systems if improved, with the exception of 9 plains. However, the performed drip irrigation plans are rare in this province and there should be more efforts to inform farmers to develop such systems in this province.

Advance velocity is an important factor in surface irrigation system design and simulation. Volume balance is a simple model based on continuity equation used in surface irrigation design and management. In the past volume balance models, it is generally assumed that the upstream depth of surface water is constant and equal to normal depth. This initial assumption may cause significant errors in computing advance flow. In this paper, a modified volume balance (MVB) model is developed to predict the advance curve in furrow irrigation. In the suggested method the upstream surface, water depth is actual depth and variable in time. Predicted advance distance of VB, VB-ZI and MVB was compared to the observed data obtained for the three furrow lengths of 60, 80 and 90m. Evaluation indexes indicated that the modified volume balance equation is more accurate than the previous equations by RMSE 9.26, 7.37 and 6.76 respectively. Sensitivity analysis showed that the inlet discharge has the greatest effect on the model and the model is more sensitive to decreasing the discharge amount than to increasing it

Flood irrigation after planting induces wetting and drying cycles in arable soils. For this reason, the effect of this process on load-bearing capacity (pre-compaction stress pc) of a fine textured soil (silty clay) was studied. In this research, large air-dry disturbed soil specimens were prepared and some of them were exposed to five wetting and drying cycles. Next, the large soil specimens with/without wetting and drying cycles were compressed under three preloads (0, 100 or 200 kPa) and then the centre section of the preloaded soil specimen was firstly submitted to a plate sinkage test (PST). Then immediately one cylindrical sample was cored for confined compression test (CCT). The results showed that for reconstructed soil samples without wetting-drying cycles, the predicted pc using PST didn't significantly differ from the applied preload. Therefore, the PST can be used to determine the load-support capacity of the tilled soils. In PST, with an increase in soil water content from 0.9PL to 1.1PL, the amount of over-prediction in pc decreased. However, wetting-drying process significantly increased over-prediction in pc at the same water content. Hence, soil compressibility does not simply depend on the actual soil water content but also on the previous history of water content changes (i.e., wetting-drying cycles).

An experiment was performed at the Miyandoab Agricultural Research Station to study yield and water use efficiency of furrow and tape irrigation systems in one-row and two-row planting patterns, and to investigate density of grain corn SC704. The experimental design was a completely randomized block arranged in Strip Split Plots with three replications in 2010. Irrigation treatments were applied in vertical plots, and planting arrays of different densities were applied in horizontal plots in the form of split plots. The vertical plots were comprised of four irrigation treatments, including three levels (80%, 100% and 120%) of water requirement by use of drip tape irrigation and 100% of water requirement in furrow irrigation, and the horizontal factor was a planting array in the form of single-row and two-row planting patterns and the sub factor was comprised of three levels: 75, 90 and 105 thousand plants per hectare. The results showed that furrow irrigation had the highest rate of grain yield, about 18.6 ton per hectare, and the treatments of tape irrigation of 120%, 100% and 80% had 18.4, 18.2 and 14.9 tons per hectare, respectively. Although the furrow irrigation treatment had higher yield than the rest, there was no significant difference between treatments except for the 80% of tape irrigation. Thus, by utilizing tape irrigation without a great decrease in the yield, water use efficiency improved. The comparison between treatments of tape irrigation of 80%, 100%, 120% and furrow irrigation led to grain yields of 2.3, 2.2, 1.9 and 1.4 kg/m3, respectively. Also, the highest water use efficiency and maximum yield were obtained from 90000 plants per hectare.

The effects of water quality, installation depth and space of subsurface drip irrigation (SDI) laterals on yield and visual quality of turfgrass were investigated. A field experiment was conducted at the experimental farm of Shahrekord University. The experimental design was a Split-Split Plot with experimental arrangement of completely randomized block design with 16 treatments and three replications. Treatments included two types of water quality: well water (W) and treated wastewater (WW), two installation spaces of SDI laterals (45 and 60 cm) and four depths of placement of SDI laterals (15, 20, 25 and 30 cm). Turfgrass indices recorded during the experiment included height, dry mass, color, visual density and growth uniformity. The ANOVA results showed that interaction of irrigation water quality × lateral spacing × installation depth of SDI laterals is significant on the height, dry mass and growth uniformity of turfgrass. Irrigation with wastewater as compared to well water produced grass with significantly higher height and more dry weight. Treatments irrigated with well water had a better growth uniformity than those treatments irrigated with wastewater. Results indicated that there was no significant effect of experimental factors on turfgrass color. The interactional effect of lateral spacing and installation depth on the turfgrass density was significant. Increasing installation depth and laterals spacing caused a decrease in turf’s yield and visual quality.

Because of limiting water resources and increasing demand for food, it is necessary to investigate the effect of irrigation systems on water productivity. This research was conducted to evaluate yield and yield characteristics of two potato varieties under sprinkler and trickle irrigation systems. The treatments were two irrigation systems (sprinkler and trickle irrigation) and two potato varieties (Burren and Satina) in a randomized complete block design with three replications. Full irrigation was done based on moisture depletion from depth of root development in both irrigation methods.. Potato yield and water productivity (WP) in drip and sprinkler irrigation systems showed significant differences (P<0.01). The highest potato yield (24.08 ton ha-1) and water productivity (3.83 kg m-3) were obtained in drip-tape irrigation and Satina potato variety treatment. Also, the lowest potato yield (12.97 ton ha-1) and water productivity (1.73 kg m-3) were obtained in sprinkler irrigation systems and Burren potato variety. The potato yield in sprinkler irrigation system was obtained 42 percent lower than trickle irrigation system. In sprinkle system, dried top weight and height of stem were respectively higher and lower than those in trickle (Tape) irrigation system for both potato varieties. Overall, trickle irrigation is suggested for cool and dry climate to increase potato yield and water productivity.

The objectives of this study were to investigate the effect of dripper discharge and irrigation time on the wetted width in the sandy loam soil with high percentage of gravel and to evaluate previously developed models of estimation of the wetted width in the previous researches. The treatments included three irrigation times (T) of 4, 8 and 12 h and three dripper discharge rates (q) of 2, 4 and 8 l/h, with three replications. The wetted width of each dripper was measured 24 hours after irrigation application. The maximum and minimum wetted widths were 159.8 and 63.5 cm for T12q8 and T4q2, respectively. A linear model was developed as a function of two variables of irrigation time and dripper discharge rate was developed to predict the wetted width in sandy loam soil with high percentage of gravel. The evaluation of recommended models of wetted width for the studied soil showed that only one of six models was accurate enough to estimate wetted width. It can be concluded that the presence of gravels in the soil has a complex effect on width and depth of wetted zone. Thus, it is necessary to measure the wetted width and wetted depth in the field.

In order to investigate the effect of different levels of irrigation on qualitative and quantitative yield and determine the corn's optimum depth of Irrigation in sShahrekord, a randomized complete block design experiment was done with 7 treatments including 40, 55, 70, 85, 100, 115 and 130 percent of soil moisture deficit and three replications in furrow irrigation. Effects of irrigation levels on yield, water use efficiency, weight of dry matter, plant height, stem diameter, median diameter, length and weight of corn were significant. Different levels of irrigation had no significant effect on seed oil and protein content, but their impact on plant fiber content was significant. With increasing depth of irrigation, stem length, grain weight and plant fiber content increased. The minimum and maximum corn yield were related to 40 and 130% of full irrigation with the yield of 43.1 and 88.1 tons per hectare, respectively. The maximum and minimum use efficiencies were 55 and 130% of full irrigation treatments with values ​​of 16.17 and 10.1 Kg per cubic meter, respectively. The result of economic analysis showed that the water consumption is 5/582 mm, equivalent to 86% full irrigation depth.

Evaluation of pollutant transportation in soil is important from different environmental aspects such as soil and groundwater contamination. The purpose of this study is to measure 2, 4-D concentrations in a silty loam soil under two different treatments (normal and deficit irrigation) in a corn field and simulate the results using the PRZM-3 and LEACHP models. Total concentrations of 2, 4-D in the soil profile in 8, 13, 23, 30, 37, and 57 days after application for normal irrigation were 18.5, 16.36, 11.67, 10.47, 8.47 and 3.2 mg kg^-1, respectively. For these dates, PRZM-3 model simulated 18.5, 16.36, 11.67, 10.47, 8.47 and 3.2 mg kg^-1 of 2,4-D, respectively and LEACHP model simulated 23.34, 20.93, 16.7, 16.3, 12.9 and 11.41 mg kg^-1 of 2, 4-D, respectively. Total concentrations of 2, 4-D in the mentioned dates for deficit irrigation were 20.2, 16.7, 11.22, 10.05, 8.8 and 7.3 mgkg^-1, respectively. For these dates, PRZM-3 model simulation results were 21.9, 19.89, 14.2, 10.62, 9.6 and 8.22 mg kg^-1, respectively and LEACHP model simulation results were 25.22, 21.3, 19.43, 18.58, 18 and 16.27 mg kg^-1, respectively. The simulation results showed that performance of PRZM-3 model was better than LECHM model in both treatments. In this research, the half-lives of 2, 4-D for 0-10 cm and 10-20 cm of soil depth were 7 and 33 days in a normal irrigation, and 9 and 34.65 days in a deficit irrigation, respectively.

Mobarakeh Steel Complex has been using treated industrial wastewater for irrigation of green space to combat water shortage and prevent environmental pollution. This study was performed to assess the impact of short-, middle-, and long-term wastewater irrigation on soil quality attributes in green space of this complex. Soils were sampled from the wet bulb produced by under-tree trickles in three depths of forested lands irrigated with treated wastewater (for 2, 6 and 18 years) or groundwater. Several chemical, physical and biological characteristics of the soil samples were determined in the laboratory and compared to those of the native unirrigated soils as the controls. The results showed that pH was significantly reduced in the wastewater-irrigated soils as compared to the control. Organic matter content and cation exchange capacity significantly increased in the irrigated soils due to the incorporation of tree leaves into soil. Soil salinity also increased as the irrigation period increased because of the relatively high salinity of water and wastewater used for irrigation. Microbial basal respiration and arginine ammonification were greater in the irrigated soils in comparison to the control. In general, forestation and irrigation management have improved most of the soil quality indexes in the Mobarakeh Steel Complex green space, but some soil characteristics, such as salinity, need to be monitored and improved in future.

The main objective of this study was evaluation of integrated management and mixing saline/fresh water on soil salinity distribution. For this purpose, a field was selected and 32 plots were made in it with a 6 m×2.5 m size. A split plot experiment was employed with two sunflower varieties (Alstar and Hisan33), four irrigation schemes (CIS) and four replications. Irrigation schemes being applied as treatments are: T1: every other irrigation with saline water (11 dS m^-1) and fresh water (2 dS m^-1) (every other irrigation), T2: fresh water - saline water, T3: mixed irrigation and T4: saline water - fresh water. Soil samples were collected from depth of 0-20, 20-40 and 40-60 cm in the early, mid and end of the irrigation season. The samples were analyzed for EC, Ca, Mg, Na and Cl. The result showed that soil salinity in depth of 40 cm is greater than salinity in depth of 20 and 60 cm in all treatments and for both sunflower varieties, in all growing stages. The maximum salinity concentration was observed in T2 among all treatments. Increasing irrigation depth has increased the soil extract’s Cl and Na in all treatments during growing season to 50 and 75 meq/L, respectively. The effects of CIS treatments are statistically significant on Ca and Mg in Alstar, and in all regimes affect on different depths. The minimum value of EC and maximum yield was observed in T4, T3, T1 and T2, respectively.

Accurate design of drip irrigation systems requires sufficient understanding of horizontally and vertically distribution of water flow in soil and modeling the wetting pattern dimensions created under the drip source. Field and laboratory activities are not suitable for this purpose considering their time and financial constraints and it is necessary to apply accurate software for determination of several equations in different situations. This research aimed to present simple models for calculation of wetting pattern dimensions in different discharges and structures in drip irrigation system. For this purpose, HYDRUS-2D model was implemented for four discharges in the same soil texture and different soil textures in the same discharge. The values obtained from running the software such as depth and maximum diameter of wetting pattern have been fitted with time values and corresponding equations were obtained. The results of statistical indices for all obtained equations (R>0.96, RMSE<2.12 and MAD<1.38) represent suitable accuracy of corresponding equations in determination of pattern dimensions under the drip source. The results also showed that Loamy Sand and Silt textures, respectively, have maximum and minimum depth and wetting pattern diameter.

In agricultural development many factors such as weather conditions, soil, fertilizer, irrigation timing and amount are involved that are necessary to be considered by the plant growth simulation models. Therefore, in this study, the values of soil water content at different depths of soil profile, dry matter production and grain yield of winter wheat were simulated using AquaCrop and WSM models. The irrigation treatments were rain-fed, 0/5, 0/8, 1 and 1/2 times of full irrigation conducted in Agricultral College of Shiraz University during 2009-2010 and 2010-2011. The models were calibrated using measured data in the first year of experiment and validated by the second year data. The accuracy of soil water simulation was used to refer to the accuracy of simulated evapotranspiration. The accuracy of soil water content at different layers of root depth in the validation period was good for the WSM model (Normalized Root Mean Squer Error, NRMSE= 0/14). But the AquaCrop model showed less accuracy for soil water content (NRMSE=0/26). However, the values of predicted and measured crop evapotranspiration were close together at full irrigation treatment, the accuracy of AquaCop predictions was decreased with inceasing water stress. WSM model has had a good estimation of the dry matter and grain yield simulation with NRMSE of 0/15 and 0/18, respectively. However, they were simulated with less accuracy in the AquaCrop model with NRMSE of 0/19 and 0/39.

Drip irrigation is one of the new irrigation methods for optimum use of water resources and increase of irrigation efficiency. The emitters' clogging is the most important problem in these systems. The physical clogging is the most important factor in reducing the discharge and emission uniformity of emitters. The emitter position on the laterals and emitter spacing are the factors that affect the physical clogging rate of emitters. The objective of the present study is evaluating the effect of emitter spacing of drip irrigation tape on the physical clogging rate of emitters. For this purpose, a physical model of drip irrigation tape was designed and made at the laboratory. In this research, seamless and seamed irrigation tapes with emitter spacing equal to 10, 20 and 30 centimeters were used. Statistical analysis showed that emitters spacing have significant effect on clogging rate of emitters in seamless and seamed drip irrigation tapes. The results also indicated that seamless irrigation tapes with 30-centimeter emitters spacing, with clogging rate of 22 percent, have the least clogging. A comparison of clogging rate and uniformity coefficient of irrigation tape showed the higher performance of seamless irrigation tape in clogging condition.