The optimal emitter spacing and flow rate for an SDI system depend on factors such as soil type, plant species, climate, and desired watering frequency. A general rule of thumb is to space emitters 12-18 inches apart, with a flow rate of 0.5-2.0 liters per hour (LPH) per emitter. However, this may vary depending on specific conditions. Conduct a soil survey and consult with an irrigation expert to determine the ideal emitter spacing and flow rate for your specific application.