تعيين تابع توزيع مناسب براي توصيف تغييرات مكاني آب به كار رفته در آبياري باراني عقربه اي

Determination of Appropriate Distribution Function for Description of Spatial Variation Application Water in Center pivot Irrigation System

Center pivot irrigation system is one of the modem irrigation methods, which is used in many parts of Iran. Due to the fast development and high utilization of this system, the concept of the optimal irrigation depth is really important for this system. This question are generally proposed that how much is the optimal irrigation depth? This parameter is usually determined without considering distribution functions and environmental protection parameters. Regarding the environmental problems and the cost of refining it, the computed irrigation depth, which gives us the maximum yield is not the optimal irrigation depth necessarily. So environmental limitations should be considered in determination of the optimal irrigation depth and itʹs necessary to determine data distribution function. In this research, according to ASAE standard, any data distribution function were determined. System layout was setup. Four radial lines of catch cans with 6m space were used. (two radial lines of catch cans A and B, were installed on the maximum slope with 3° between every two rows and two radial lines of catch cans C and D, were installed on the minimum slope with 3° between every two rows). Field data were collected with different speeds of the center pivot system. The amount of water in the catch cans were measured in different weather conditions (wind speed, weather temperature and relative humidity) proposed distribution function in sprinkler irrigation (normal, lognormal, specialized power and uniform distribution) were selected. Nonparametric statistic test (Kolmogorov-Smirnov) is used. Results show that specialized power and uniform distribution were failures at the 0.05 confidence level in all of the tests (20 out of 20). Lognormal distribution function had 17 cases of failures (17 out of 20) at the 0.05 confidence level normal distribution function had 5 cases of failures (5 out of 20) at the 0.05 confidence level. So, normal distribution function shows the best description for dispersion data. It is suggested that for center pivot irrigation system, the optimal irrigation depth should be determined by using normal distribution.