Estimation of different soil infiltration Parameters in furrow irrigation with super absorbent Polymer

Abstract
Background and objectives: Limitation of water resources in the country and devoted the large amount of it to agricultural and natural resources, would be a crucial and vital issue in increasing the efficiency pattern and water use. In this regard, applying modern technology such as super absorbent polymer may play the significant role in decreasing the dry stress in the arid and semi-arid regions Super Absorbent Polymers lead to increase soil water capacity and thus improve the water application efficiency. Surface irrigation, due to its simplicity, is regarded as the most common method of irrigation. Determination of the parameters of water infiltration in soil, is one of the essential steps in the designing and the management of surface irrigation systems. The purpose of this study is precision the impact of super absorbent polymer analysis in estimating infiltration parameters methods in furrow irrigation and choosing the best method based on combination of superabsorbent polymers in the field of the study.
Materials and methods: The experiment were performed in the educational farm of the Gorgan university of Natural Resources and Agriculture in a no cultivation conditions. In this research four combinations of superabsorbent polymer A200 with soil which were composed of 0, 7, 11, 16 gram of polymers in square at a depth of 25 cm and the electric current of 0.75 liter per second were considered. The experiment were arranged as randomized complete design with four replications. In this research accuracy of four infiltration methods consist of Elliott and Walker two-point method, Benami and Ofen advance method, Shepard et al., and Valiantzas et al., one-point methods. Then, it simulated by SIRMOD software and full hydrodynamic model in different steps of irrigation such as advance phase, Recession phase and infiltrated volume in furrow irrigation.
Results: Ithe results showed that the minimum average relative error (RE) in prediction of infiltrated water is devoted to Elliott and Walker and Shepard et al. methods with 1.88 and 20.8 percent minimum and maximum respectively for estimating total infiltrated volume.in the other hand, results indicated that the average standard error in prediction of advance phase time is devoted toElliott and Walker method is 1.02 percent which is the minimum percentage of error and maximum of percentage of error is 22.13 percent in the method of Sheppard et al; and in prediction the the time of recession phase Elliott and Walker method (1.62 percent) had the minimum standard error.
Conclusion: The results of this research showed that Elliott and Walker method has the best evaluation in prediction of the volume of infiltrated water, advance phase and recession phase and so increasing the amount of polymers and irrigation stages showed that Elliott and Walker two-point method and and Shepard et al., one- point method has the decreasing trend in error percent. .
Keywords: A200 polymer, Advance phase, Recession phase, SIRMOD software, Surface irrigation.