JWSS - Journal of Water and Soil Science

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A computer model (SprinklerMod) was developed to simulate hydraulics of sprinkler irrigation systems. The objective of this paper is to describe mathematical background of this model for simulating pressures and discharges of sprinklers along the laterals. The model is capable of designing two types of laterals: laterals with fixed sprinklers and laterals with portable sprinklers. The model shows the simulation results in the forms of tables and graphs. Laterals with one or two diameters on uniform or non-uniform slopes can be designed. The model provides graphical presentation of percentage of sprinkler pressure variations for different lateral inside diameters. The Hazen- Williams equation was used for the calculation of friction losses. The required input parameters for lateral simulation are lateral type, desired sprinkler operating discharge and pressure head, spacing between sprinklers, distance of first sprinkler from lateral inlet, number of sprinklers operating on the lateral, riser height, Hazen- Williams pipe friction coefficient and lateral longitudinal slope or field elevations at each of the sprinklers on the lateral. Laterals are simulated such that average sprinkler pressures and discharges become equal to the values requested by the designer. Iterative procedures were implemented to simulate sprinkler pressures and discharges on laterals and the Newton- Raphson iterative method was used for calculating pressure of each of the sprinklers on the laterals with portable sprinklers. In order to evaluate the model, some example results of the model were compared with classical design results. Since there is no formula for the calculation of the required lateral inlet pressure in classical design of laterals with portable sprinklers in the scientific references, a new formula was developed. Averages of absolute percentage of variations of lateral inlet pressures for laterals with fixed sprinklers and with one or two-size diameters ranged from 0.3 to 0.7 percent, respectively. This value for laterals with portable sprinklers was 0.1 percent. 

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Global solar radiation (Rs( on a horizontal surface in the estimation of evapotranspiration of plants and hydrology studies is an important factor. Average daily global solar radiation on a horizontal surface was estimated by artificial neural networks (ANNs) and five empirical models including FAO (No.56), Hargreaves-Samani, Mahmood-Hubard, Bahel and Annandale. The weather data was selected from Karaj, Shiraz, and Ramsar weather stations, which have arid, semi arid and very humid climates (based on De Martonne classification). Daily solar radiation was measured at the three sites selected. The ANN, with actual duration of sunshine and maximum possible duration of sunshine as input parameters, generated daily solar radiation estimates with highest level of accuracy among all models tested. Rs estimates by ANNs with only temperature indices as input and by Hargreaves-Samani, Annandale and Mahmood-Hubard, which are all temperature oriented models, had lower accuracy at all three sites. In contrast, ANNs with actual duration of sunshine and maximum possible sunshine hours as inputs in Karaj, Shiraz and Ramsar station with root mean square error (RMSE) of 2.08, 1.85 and 2.05 Mj m-2 day-1 respectively were the best models. After ANNs, FAO-56 model which is based on sunshine hours produced results closer to the measured values. Rs estimates by ANNs with only temperature indices as input and by Hargreaves-Samani, Annandale and Mahmood-Hubard which are all temperature oriented models, had lower accuracy at all the three sites. These models are not appropriate for estimating daily global solar radiation.

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Nitrate leaching from agricultural lands can pollute groundwater, and the degree of pollution caused significantly depends on agricultural practices implemented on farms. Field studies required to evaluate the effects of various agricultural management strategies on nitrate leaching are expensive and time consuming. As a result, it is suggested to use crop models to simulate the effects of management practices on nitrate leaching. Plant growth models such as DSSAT software package can simulate daily plant growth and development, and also are capable of simulating daily nitrate leaching and nitrogen uptake by plants. However, it is required to evaluate the performance of any model before using it for any specific region. In this study, the performance of nitrogen balance model of DSSAT software package was evaluated to simulate nitrate leaching from the root zone of silage maize at different levels of applied water and nitrogen fertilizer. The experiment consisted of three levels of nitrogen fertilizers, including zero, 150 and 200 kg N ha-1 and four levels of applied water 0.7SMD (soil moisture depletion), 0.85SMD, 1.0SMD and 1.13SMD. Nitrate-nitrogen leaching from 36 plots at the 60 cm depth during the growing period was measured by soil moisture suction equipment (ceramic suction cups, CSC). After calibrating the model by using field data, its performance was evaluated to simulate nitrate leaching. Maximum amount of N leaching 8.4 kg N ha-1 was obtained from over irrigation treatment with the application of 150 kg nitrogen per hectare. The model simulated nitrate leaching for this treatment as 7.8 kg N ha-1. The model consistently underestimated the nitrate leaching however, it followed the behavior of nitrate leaching during the growing season. In deficit irrigation treatments, the nitrate leaching was very low and close to zero and the model simulated the same result accordingly. The results showed that the model, in addition to phenological stages and performance indicators, can simulate nitrate leaching from the root zone and could be used to evaluate the effects of various irrigation and fertilizer management strategies on nitrate leaching.

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Since more than 75% of the rice fields in Iran are located in the Northern provinces i.e. Mazandaran, Guilan, and Golestan identifying the crop water requirement of rice fields is essential for water resources planning in the Northern provinces. The objective of this research was to ascertain the crop water requirement of two rice cultivars namely Hashemi and Khazar in Guilan province during 1389 growing season. Four iron barrels with diameter of 56 cm were used as lysimeters to grow the cultivars mentioned. According to a simple volume balance approach the crop water use of the four lysimeters were determined during the growing season. The elements of volume balance approach such as the depths of drainage, precipitation, and irrigation were recorded daily and the average of 5-day and 10-day periods were reported. The daily rice crop water use during the growing season was found to range from 2.4 to 6.3 mm/day with a seasonal crop water use ranging from 430 to 470 mm for Hashemi and Khazar cultivars, respectively. Daily reference evapotranspiration was computed by the FAO-Penman-Montith equation and accordingly rice crop coefficients were computed. The crop coefficient of Hashemi variety was found to be 1.1, 1.3, and 1.1 during the initial, mid, and end growth stages, respectively. In addition, the aforementioned parameters for Khazar variety were 1.2, 1.3, and 1.1.

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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.