To achieve the most economical irrigation, some of the following irrigation methods and techniques can be used:

1. Drip Irrigation System: Drip irrigation is an efficient irrigation method that delivers water drop by drop directly to the roots of plants. This system reduces water waste because the water is only delivered to the roots of the plants and does not get blown away by the wind or evaporate. Drip irrigation also reduces the risk of soil erosion and pests and diseases.

2. Sprinkler irrigation system: Sprinkler irrigation system can cover a large area of land by spraying water mist or water droplets onto crops. Properly designed sprinkler irrigation systems can reduce water waste and ensure that water is evenly distributed across farmland.

3. Intelligent irrigation control system: Using modern technology, such as sensors, meteorological data and automatic control systems, intelligent irrigation management can be achieved. This kind of system can automatically adjust the amount and time of irrigation water according to actual needs to avoid over-irrigation.

4. Soil Moisture Monitoring: Use soil moisture sensors to monitor moisture levels in the soil to ensure irrigation is only done when needed. This avoids unnecessary irrigation and reduces waste.

5. Shade and mulch: In hot areas, use shade netting or mulch to reduce evaporation of soil moisture, thereby reducing irrigation needs.

6. Plant selection and planting density: Select plant varieties that are adapted to local climate and soil conditions, and optimize planting density to maximize the use of limited water resources.

7. Rainwater collection and storage: In areas with abundant rainwater, collecting and storing rainwater for irrigation can save a lot of freshwater resources.

8. Regular maintenance and inspections: Regularly maintain and inspect irrigation systems to make sure they are operating properly and are not leaking or wasting water.

The most economical irrigation methods usually combine a variety of techniques and strategies to select the most appropriate irrigation method based on specific farm conditions and needs. In addition, the time and amount of irrigation should be adjusted according to the growth stage of the plants and meteorological conditions to ensure optimal water use efficiency.