English abstract
Oman is located in an arid climatic zone; annual rainfall ranging from 50 to 300 mm with average of 100 mm. Ground water is the main source of fresh water. More or less 90% of water is consumed by the agricultural production. Most arable lands (48%) are clustered in Al-Batinah region. However, the increased demand of water for agriculture has distressed the water table and recent research findings have revealed that most farm land are being affected by salinity issues, caused by the over pumping for irrigation and seawater intrusion into coastal aquifer in Al-Batinah region. The aim of the research study was to create appropriate methodology to develop modern irrigation systems and proper irrigation scheduling without affecting the farmers and the water table. The aim of the pilot study was to evaluate the performance of the developed sensor-based system, compare and solve the problems related to it. Over- irrigation is one of the problems observed in sensor-based irrigation system in this study. Calibration models for the VH400 sensors were developed as one of the specific objectives.
The developed methodology consisted of four field plots divided according to irrigation systems used; ET-based, time based and two of sensors-based. For ET-based system, historical weather data were used to compute the CWR for okra plant with aid of CROPWAT8.0 software. The time-based system was a modification of ET-based system with timers for irrigation scheduling. While, in sensor-based system, soil moisture sensors (VH400) were used to monitor VWC of soil and to trigger irrigation. The threshold values were obtained using standard methods of estimating FC and PWP. Three replicates were used to calibrate the two VH400 sensors and 5MT sensor in each pot experiment. This was done by saturating the pot and collecting the sensor readings until PWP was reached. Four statistical analysis; R2, MBE, RMSE and K were conducted to test the accuracy of developed calibration models. The main findings of the study were; the graphical representation of the CWR which was in decreasing trend due to the approaching winter in Oman during the crop period. In theory, and based on literature the sensor-based irrigation system is the best for scheduling irrigation followed by ET-based. The amount of water applied during crop period of one month was 3,344 and 3.379 m for ET and Time-based irrigation respectively. The amount of water saved was only 35 liters (1%). Over-irrigation had occurred in the sensor based plots, which made it difficult to analyze its data. In the calibration process, three segmented calibration models were obtained which showed biased error compared to the company provided models. The estimated value for FC and PWP were 37.44% and 12.39% respectively. Statistical analysis showed good accuracy of the developed models. Moreover, the sensors evaluated in this study seem to require unique sensor orientation and soil-specific field calibrations and further investigation are required to verify the performance of the developed models under field conditions.
