Drip line size selection in micro irrigation design for tree crops: economic and energetic sustainability

The proper selection of components in an irrigation system can help increase water use efficiency, also reducing costs and saving energy. In the design of drip irrigation systems, characterized by the supply of low water rates, multiple factors are considered: soil type, field length, crop irrigation requirements, distribution uniformity, sector size and number, etc. The present work analyses the criteria for choosing between two different diameters of drip tubing, commonly used in tree crops, considering the technical parameters available and the economic and energetic implications. The analysis considers not only the difference in upfront costs for materials, but also the operation costs, particularly for pumping energy, over the lifetime of the irrigation system. Three scenarios are analyzed, based on the annual operating time of the system: 400, 600 and 800 h. Each scenario is studied for two available diameters of the drip tubing, i.e. Sixteen mm and 20 mm. The spacing between the drippers on the line was chosen at 70 cm, while the effects produced on the system by four different flow rates (L h^‑1) are analyzed: 1.0, 1.6, 2.4 and 3.8. The combination of these parameters determines the operating pressure required for the system and the maximum line length achievable. The technical-economic analysis carried out shows that an economic advantage is obtained with the adoption of larger diameter lines (20 mm), which increases along with extended irrigation time, higher flow rates and longer lines. The maximum advantage, equal to 153 € ha^‑1 year^‑1 (+48%), is obtained by irrigating 800 h year^‑1 shifts, with flow rates of 3.8 L h^‑1, over maximum line lengths of 187 m. Under these conditions, the energy saving is also maximum with a 57.1% reduction in pumping energy consumption, equivalent to 3,874.95 kJ ha^‑1 year^‑1.