English abstract
Date palm is the most important crop in the Sultanate of Oman. It is widely distributed in the country, with the exception of the southern region of Dhofar. As water resources in the country are limited, there is a pressing need to assess the crop water requirements of this important crop under local conditions. This thesis presents the results of a study conducted at Al-Rafaa farm in Nizwa in Oman's interior. Plots of mature date palms (Khalas variety) were selected for the study. The soil-water balance method was used to estimate the temporal distribution of the crop coefficient of date palm under both modern and traditional irrigation systems. The study was accomplished using Time-Domain Reflectometry measurements of the soil-water content, a computerized irrigation scheduling package (SCS Scheduler), and meteorological data from an automated weather station at the site. The study produced baseline information on the crop water requirements of date palms in the interior region of Oman under both types of irrigation systems.
The study demonstrated that annual evapotranspiration for date palms (ET.) under the traditional falaj irrigation system was higher by 18.6% compared to the modern bubbler irrigation system. The annual ETC under the traditional falaj system was 2647 mm while the ET, under the bubbler irrigation system was 2232 mm. The average daily ETC was 7.25 mm and 6.11 mm for date palm trees under the traditional and bubbler irrigation systems, respectively.
The temporal crop coefficient curves generated in this study show little difference under the two systems. The basal crop coefficient ranges from 0.9 to 1.44 for date palm trees under the bubbler irrigation system and 1.03 to1.55 under the traditional system. The difference can be attributed to the way the two systems were managed. The increased evaporation from the soil surface under the traditional system, in which the entire surface is wetted, contributes to the observed increase in water use. Moreover, weeds tend to grow over the entire area under traditional irrigation while they are limited to the basins of the trees under bubbler irrigation. This will increase the overall water use efficiency of the modern system compared to the falaj system.
The wet-dry irrigation cycle practiced in the traditional falaj system enhanced date production, although the dates produced under the bubbler system were of better quality. While it is inconclusive to rely on only one season to make definite conclusions on the production of dates, it should be pointed out that the average production of dates under the traditional irrigation system was 80.9 kg/tree while it was 60.5 kg/tree under the bubbler system. This could be due to the excess water used under the traditional system since the water use efficiency under the bubbler irrigation system was high compared to that of the traditional system.
The soil water regime under the traditional falaj system shows that the soil water exceeded the field capacity during irrigation with an excess irrigation of 336 mm for the whole year. However, the soil moisture dropped below the management allowable depletion level of 60% before irrigation. On the other hand, t1 regime under the bubbler irrigation system shows less fluctuations and very limited excess of irrigation.
