EFFECT OF SPATIAL DISTRIBUTION OF SOIL MOISTURE AND HEAT CONTENT ON IRRIGATION SCHEDULING OF SOME CROPS GROWN IN EL-SHEIKH ZUWAID AREA, NORTH SINAI - EGYPT

The current research aims to study the effect of spatial variability of soil moisture and soil heat content on irrigation scheduling of olive trees and tomato plants under drip irrigation system in desert sandy soil of North Sinai Governorate.
Field experiment has been conducted in El-Sheikh Zuwaid experimental station in North Sinai during 2011 growing season. The studied area includes two sites: one cultivated with olive trees and the other with tomato crop. Three profiles were examined in each site to verify the spatial variability of soil moisture and three infiltration tests had been carried out. Physical and chemical analyses were carried out for the soil profiles. Meteorological data were collected for the 15 last years of the site as the irrigation schedules were designed for the tested two crops. The measurements of soil moisture and soil temperature were carried out over the studied growth season which lasted to 6 months. The data show the following:
1-     Infiltration rate (IR) values express the horizontal spatial variability among profiles, while the soil moisture characteristics express the vertical one.
2-     The intake rate of water into soil is affected by soil texture, plant cover and soil bulk density. The latter influences the water infiltration to soil as the differences reach to double in olive and 20% in tomato. Olive farm gives the lowest IR values while tomato gives the highest ones.
3-     Soil moisture shows great differences due to the differences in particle size distribution (soil texture), its content increased gradually from March to August coordinated with soil temperature as well. On daily base, the moisture content shows declination through daytime while get maximum levels at night. Meanwhile, soil moisture fluctuations were more detected under olive than under tomato due to the difference in coverage rates for both. So, intercropping of tomato is recommended through olive lines as the assumption has been verified statistically.
4-     There were positive significant correlations between moisture content and each of available soil moisture, soil temperature and soil heat content under tomato farm. But for olive no significant correlation was found between moisture content and available soil water, but the rest variable were significant.
5-     Soil temperature increased from March to August, being higher than air temperature from March to May but lower from June to August. Minimum soil temperature was recorded at daytime hours while the maximum were at night time. Soil temperature values were coordinated with soil moisture ones. The soil heat content values show the same trends of soil temperature.
6-     Some modification on irrigation schedule has been undertaken adjust the soil moisture at desired level of depletion, where two calculations had been carried out:
a-     Modifying the depletion level to compensate the loss of water curve, so, creating new irrigation intervals.
b-     Back calculation using the new intervals reaching to new crop coefficient (Kc). Modifications for olive from 14 – 25 to 11 – 22 days with the same irrigation amount, for tomato from 3 – 7 to 2 – 5 days with the same irrigation amount, but with modifying Kc for the modified intervals the gross irrigation amount change from 1029 to 1177 and 2404 to 2678 m³/fed/season for olive and tomato, respectively.
7-     Significant positive correlations were found between available soil water and irrigation scheduling for both olive and tomato crops.
8-     Intercropping hypothesis was checked statistically and the resulted relations were all significant.
The work concludes the importance of spatial variability of soil characters and their effect on irrigation scheduling. Furthermore, the back calculation for adjusting the soil moisture regime could be resulted in new irrigation intervals and Kc values. Also, the concept of intercropping under such similar conditions is quite acceptable.