Design of Sprinkler Irrigation Subunit of Minimum Cost with Proper Operation. Application at Corn Crop in Spain

MATLAB (TM) software named PRESUD (Pressurized Subunit Design) was developed to identify the optimum solid set sprinkler irrigation subunit design with a criterion of minimizing the annual water application cost (C-T). This C-T is defined as the cost per cubic meter of water applied to the soil for crop use. In this study, only rectangular subunits are considered, using an iterative method for calculating the lateral and manifold pipelines. The results indicate that water cost (C-w), which includes the investment and operation costs for pumping water from the source to the subunit inlet, makes up 75 % of C-T. Another important factor is energy cost, which comprises 14 % of C-T. The remaining variables, such as sprinkler spacing and layout, or application rate (AR(a)), have a lower impact on C-T. In cases of use groundwater, the proportion of energy cost in C-W can reach 40 %; thus, energy is an important part of C-T. Results shows that the criterion of limiting the maximum difference in pressure heads in the irrigation subunit (Delta h<20 %), widely used when designing a sprinkler irrigation subunit, does not always lead to a minimum C-T, and the use of tools such as PRESUD can help obtain better solutions.