الفهرس Only 14 pages are availabe for public view
 |  | from | 74 |  |  |
| | | from | 74 | | |
Abstract
Objectives of this study were:
1.Assessment of most suitable conditions for operating central pivot irrigation system to optimize its operation efficiency.
2.Study the effect of different irrigation regimes on productivity, quality and water use efficiency of Onion crop, under central pivot irrigation system.
3.Determination of distribution uniformity under different operating pressure (150, 200, 250 and 300 kPa), two sprinklers heights from plant canopy (1.5 and 2.5m), different air temperature were measured many times all over daylong, morning, afternoon and evening using (Memory Digital Thermometer, from Curtin Matheson Scientific Inc.). The following temperatures were chosen to measure the water distribution uniformity 30oC (in the morning), 35oC (2:0 pm) and 32oC 5:0 pm) and different wind speeds were measured using hand anemometer for instantaneous values of wind velocity and direction (1.4, 5 and 6 m/s).
4.Determination of the soil moisture content and salt concentration distribution at different heights (1.5 and 2.5m) before and after conducting the irrigation.
5.Three irrigation treatments of water i.e., (50%, 75%, and 100% of Etc) with three replicates had been investigated.
Determination of the Growth parameters for onion crop (Plant height, number of blades, area of blades, fresh and dry weight of blades, and fresh and dry weight of bulbs), and determination of the Total dissolved solids (TSS) as percent of the onion sap.
6.Determination of the total bulb yield, (ton/fed).
7.Determination of the water use efficiency (kg/m3), which computed by dividing the yield (kg) / total applied water (m3).
8.Determination of the Fertilizer use efficiency (kg/kg N), which computed by dividing the grain yield (kg) / total applied nitrogen (kg N).
The main results in this study are summarized in the following points:
1.Water distribution uniformity values decreased from 97.5 to the values 95.7, 90.5 and 85.6 % with decreasing the operating pressure from 300 kPa to 250, 200 and 150 kPa, respectively, when the nozzles height were on 1.5 m above soil level.
2.The decrease in water distribution uniformity with decreasing operating pressure can be explained in the height of the lower precipitation of water (depth in the measuring cans) towards the end of pivot arm, mostly, due to increasing friction losses especially under the lower operating pressures, i.e., 200 and 150 kPa.
3.Water distribution uniformity had decreased from 97.5 % (T = 30oC in the morning) to 90.5% (T = 35oC at midday) and increased again to 96% (T = 32oC on sunset), at sprinklers height of 1.5m and operating pressure of 300 kPa. This can be attributed to the increase of the resultant evaporation rate due to increasing of temperature.
4.Water distribution uniformity had decreased from 97.2% to 91.2, 81.7 and 69.5%, when the wind speed increased from 1.4 m/s to 3, 5 and 6 m/s, respectively. Obviously, this effect may be attributed to the increase in the drift of the small water DROPlets by wind.
5.Water distribution under onion crop was identified at three points along the pivot lateral (15, 30 and 45m) and three depths at root zone (0-15, 15-30 and 30-45cm) before and after irrigation under different irrigation levels (50, 75 and 100% of ETc). Soil moisture distribution under center pivot was determined within an irrigation cycle (7 days) according to data presented in Figs. 12 and 13, just before irrigation (at the end of irrigation cycle), and after 2days of irrigation (at nearly the field capacity), it is clear that the average water content before irrigation in the root zone up to 45 cm depth increased by increasing irrigation water level, i.e., moisture content 14.41, 25.25 and 29.50% for 50%, 75% and 100% of ETc respectively, at sprinklers height 1.5m above ground surface and operating pressure 300 kPa.
6.The salt concentration at the upper layer of soil was little higher than that at the subsurface layer before irrigation, especially for 50% and 75% irrigation rates while for the 100% rate the salts were homogenously distributed throughout the soil depth (0.37 dS/m). Generally, the average concentration of the salts was very low and the soil can be classified as non saline soil. The general averages of the soil for 50%, 75% and 100% of ETc were 0.4, 0.36 and 0.37 dS/m, respectively.
7.The highest of growth parameter and yield measurements at 75% Etc.
8.The highest of yield of onion was (5.8 ton/ fed) recorded at irrigation water rate of 75% Etc
9.The maximum value of water use efficiency was 23.6 kg/m3 with applying 50% ETc. While, the minimum value was 10.8 kg/m3 at 100% ETc.
10.The highest value of fertilizer use efficiency was 221.9 kg/kg N when applying 75% of ETc