PREDICTION OF SURFACE AND SUBSURFACE WATER DISTRIBUTION UNIFORMITIES UNDER CENTER PIVOT SYSTEM

Abstract

Field experiment was conducted in Thirthar region , Al-Anbar governorate in sandy loam textured soil. The study aimed to evaluate water uniformity for a center pivot system (Valley type). The uniformity water disribution of above and below soil surface was evaluated along the main line and in the direction of the system movement. Three sprinklers’ heights, which were 50, 100 and 130 cm, have been considered during the field experiment. The water cans container depths were used to assess the above soil surface uniformity. The average volumetric soil water contents were measured at three soil depths, 10, 20, 30 and 40 cm, to assess the below soil surface uniformity. The measurements were taken after 24, 48, and 72 hours from the time of irrigation. The results showed that the sub-surface uniformity is higher than the above soil surface uniformity. On the average, there was a noticeable decrease in the surface soil uniformity measured along the main line (68.4 %) compared to that measured in the direction of system movement (80.5 %). On the other hand, there wasn’t much difference in the subsurface uniformity measured in both directions (88.2 % along the system movement and 89.1 % along the system line). The results also was revealed that the subsurface uniformity is less affected by the sprinkler height compared to the surface uniformity. Relationships between subsurface and surface uniformities have been uniquely developed. The presented equations can be used to predict subsurface uniformity from surface uniformity with insignificant errors.