Optimisation of the design of pressurised irrigation systems for irregular shaped plots

Abstract

A software tool has been developed to support decision-making in optimising the design of pressurised irrigation systems (sprinkler and drip irrigation) for agricultural fields with sub-plots of any shape or topography. The tool determines the design with minimum total water application cost (CT) (investment + operation). This study analysed the effect of field size, shape and slope on CT and emission uniformity (EU) for drip irrigation systems for almond and pepper, as well as two possible layouts for a maize crop for permanent sprinkler irrigation systems. The minimum CT design used polyethylene lateral pipes of 13.6 mm internal diameter at 250 kPa for drip irrigation and polyvinylchloride pipes of 46.4 mm internal diameter at 600 kPa for the permanent sprinkler irrigation systems, except in certain cases of where there were triangular plots. In the drip irrigation fields, which were more irregularly shaped and had the largest plots, the lowest CT was achieved with regulated flow emitters which in this study had an emission exponent x = 0.1. This was due to their increased efficiency and therefore decreases volume requirements. The use of pressure compensating drippers is recommended for large sub-plots (>1.5 ha in the analysed cases) with irregular shape and large slopes. Under the conditions studied, the 15 × 15-m layout had a slightly lower CT than the 18 × 18-m layout because it had greater uniformity and its increased irrigation efficiency reduced water consumption, despite having somewhat higher energy consumption and investment requirements than the 15 × 15-m layout.