Using the CR index in the optimal design of a row irrigation system with the SIRMOD model

Introduction
Water scarcity is an increasingly critical global issue, causing a rise in arid lands and highlighting the need to address wasteful water usage in agriculture. Population growth, climate change, industrialization, and human conflicts have exacerbated water shortages, particularly in arid and semi-arid regions. According to the Falcon Mark index and the United Nations, Iran is experiencing water stress and a severe water crisis, threatening food security, economic development, public health, and national security. With over 92% of water consumption attributed to the agricultural sector, efficient water usage and reducing irrigation system losses are paramount. This study focuses on improving furrow irrigation efficiency by investigating surface irrigation efficiency and providing appropriate solutions.
 
Materials and Methods
The SIRMOD model, capable of simulating hydraulic surface irrigation, was employed to obtain the cut-off to Advance Time Ratio (CR) indicator. Diagrams based on soil texture, inflow rate, farm length, and the CR indicator were generated to enhance the design and efficiency of furrow irrigation systems. To ensure the accuracy of the simulation and results, the SIRMOD model was validated, and optimal CR indicators were determined for a furrow irrigation system with four different lengths and sandy-loam textured soils. A suitable field under the row irrigation system was selected, and the soil texture was determined using double-cylinder tests. Field operations included establishing forward and backward stations and smoothing the water path to prevent water from exiting the furrow. A pipe at the end of the furrow measured the output runoff using the volumetric method, and standard siphons were chosen to maintain the input flow rate. After turning on the siphons, advance and retreat times were recorded, and instantaneous runoff was estimated during irrigation. This process was repeated for three inflow rates: 0.5, 0.8, and 1.15 l s^-1, with three repetitions for each rate l s^-1.
 
Results and Discussion
The advance times in the first, second, and third furrows were 44.22, 45, and 42.88 min, respectively, while the water recession times were 293.1, 290.73, and 292.7 min, respectively. The relatively high water speed in light-textured soils and the short water regression times indicated the light texture of the farm soil and validated the test results. For an inflow rate of 0.5 l s^-1, measurements revealed that half of the water volume entered the furrow along its length, while the other half exited as runoff. Simulation results for an inflow rate of 0.5 l s^-1 yielded CR values of 8.37 for a 100 m length, 6.99 for a 120 m length, 5.41 for a 150 m length, and 3.31 for a 200 m length. For an inflow rate of 0.8 l s^-1, optimal CR indicators were 8.0, 7.25, 6.19, and 4.63 for lengths of 100, 120, 150, and 200 m, respectively. At an inflow rate of 1.15 l s^-1, the optimal CR indicators for lengths of 100, 120, 150, and 200 m were estimated to be 7.42, 6.53, 6.11, and 5.06, respectively.
  
Conclusion
The study's findings highlight a significant breakthrough in optimizing water usage in agriculture, a sector heavily reliant on water resources. By meticulously experimenting with different inflow rates and furrow lengths, the highest water application efficiency was attained with a specific set of parameters. An inflow rate of 0.5 l s^-1, coupled with a furrow length of 200 m, resulted in an impressive water application efficiency of 83%. This efficiency correlates with a cut-off to advance time ratio (CR) value of 3.31, indicating a well-balanced water distribution system. The implications of this discovery are far-reaching, especially in regions facing water scarcity and agricultural challenges. By implementing these optimized settings, farmers can maximize their water usage while minimizing waste. This not only ensures the efficient utilization of a precious resource but also contributes to sustainable agricultural practices. Furthermore, the consistency in results, achieved through the SIRMOD model's validation, underscores the reliability of these findings, providing a solid foundation for future irrigation system designs and improvements. The expanded text emphasizes the significance of the study's findings, highlighting the efficient water usage and its potential impact on sustainable agriculture, especially in water-scarce regions. It also underscores the reliability of the results through the model's validation, providing confidence in the optimized settings for furrow irrigation systems. The best water application efficiency in the farm, 83%, was associated with the inflow rate of 0.5 l s^-1 and the length of 200 m, and the CR equaled 3.31.