الفهرس 
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Abstract
Homogeneity of the distribution of water under central pivot of irrigation system was studied. To study the effect of soil properties on the efficiency of soil water distribution and its relationship with homogeneity of added water from the irrigation system as a function of time. This study aimed also to test the use of a spectral reflectance in detecting soil water content after irrigation to assess the possibility of using this device to predict the soil water content. Field experiments were carried out in the experimental farm of the Faculty of Agriculture, Ain Shams University, located in the vilage of Shalakan, Qaliubiya governorate. The studied soil is located between coordinates
Longitude 30º 12- 53=, 30º 12- 53=, 30º 12- 50=,30º 12- 51=
latitude 31º 08- 01=, 31º 07- 57=, 31º 07- 58=, 31º 08- 01=
To study the relationship between the homogeneity of the distribution of irrigation water on the distribution of water in surface soil and time after irrigation. Spectral reflectance was used to find a relationship between water content of the surface soil and % of the spectrum reflected from the soil after calibration with the gravimetric soil water content. Collection pans were used to collect water under the irrigation system of the central pivot of diameter = 15 cm and height = 23 cm at the points of intersection of the lines which make the distance between each pan and the surrounded ones was 10 meters from all sides. To estimate the coefficient of uniformity of water distribution under the central pivot a reflectance spectroscopy was used to detect soil water content after irrigation as a function of time and after calibration of the device. Generally, the coefficient of distribution of water under the irrigation pivot = 78.4%, while soil water distribution has values varying with time after irrigation. Redistribution of soil water is the main process which makes the content of the soil water tends to balance, so the coefficient of soil water distribution was increased as a function of time after the end of irrigation, 81.2%, 85.3%, 92.7% 95.6%, 97.4% after 1 - hour , 24 - hour, 48-hour , 72 -hour and 96-hour from the end of irrigation, respectively. With regard to the effect of soil properties on the distribution of water by the estimation equation of water depletion curve to show the time required to reach the equilibrium of soil water (field capacity) and increasing homogeneity of the distribution of water with time after irrigation. The obtained results can be summarized as follow :
1 - from the soil characterization data we can noticed that the studied soil is non-saline and non-sodic with medium texture (sandy clay loam)
2 – Chemical properties of water used for irrigation represent the first class, and therefore it suitable for all crops
3 - value of the slope of water characteristics curve – represented in first order (linear) equation = - 0.1025 and this value is in harmony with the texture class of the studied soil.
4 – Soil water depletion curve as a function of time showed that soil water content is equilibrate after about 72.5 hours from the end of irrigation.
5 - The average of soil water content at equilibrium after the abovementioned time = 0.3546
6 – The relationship between soil water content and % of the reflection spectrum using different wave-lengths after an hour from the end of irrigation showed closely and highly significant using all wavelengths under study (470-700 nm) 7 – The relationship between soil water content and % of the reflection spectrum of the wave lengths after 24 hours from the end of the irrigation is closely and significant, but with the wavelength 700 nm only.8 – With progress of time after irrigation – soil became unsaturated – so, the correlation between soil water content and % of the reflection spectrum, became nonsignificant especially with the wave lengths less than 700 nanometers.