Design of microirrigation subunit of minimum cost with proper operation

Matlab software named PRESUD (Pressurized Subunit Design) was developed to identify the optimum microirrigation subunit design using the annual water application cost per unit of irrigated area (C _T). This is defined as the cost per cubic meter of water applied to the soil for crop use, calculated as the sum of investment, maintenance, energy, and water (C _w) costs. In this study, only rectangular subunits are considered, using an iterative method for calculating the lateral and manifold pipelines. The infrastructure necessary for water delivery to the subunit inlet was taken into account in the price of water. The results indicate that C _w is the most important factor in C _T, which includes the investment and energy costs for moving water from the source to the subunit inlet. Other important factors, in order of importance, are the emission exponent (x), coefficient of variation of emitter manufacturer (CV_qmf), and emitter spacing (s _e). The minimum water application cost for a typical subunit to irrigate vegetable crops such as pepper is obtained with a subunit of 0.3–0.5 ha, with 80 m of paired lateral pipe length of 16 (13.6 mm) PE 0.25 MPa diameter, and 50 (44 mm) PE 0.4 MPa of manifold pipe diameter. The cost of a typical drip irrigation subunit design for a crop, such as grapevines on trellises, is equivalent to 25 % of the C _T of a typical subunit to irrigate vegetable crops, such as pepper.