Write four types of gravity-fed irrigation.

1. Drip irrigation: In drip irrigation, water is delivered directly to the roots of plants through a network of tubes and emitters. This method is efficient and minimizes water waste by delivering water only where it is needed.

2. Sprinkler irrigation: Sprinkler irrigation involves spraying water over the plants in a circular or oscillating pattern. This method is commonly used for larger areas and can be adjusted to deliver water at different rates depending on the needs of the plants.

3. Flood irrigation: Flood irrigation involves flooding the fields with water and allowing it to soak into the soil. This method is simple and cost-effective but can lead to water wastage and soil erosion if not managed properly.

4. Furrow irrigation: Furrow irrigation involves creating small channels or furrows between rows of plants and allowing water to flow through them. This method is commonly used for row crops and can be adjusted to deliver water at different rates depending on the needs of the plants.

1. Surface Irrigation:
- Furrow irrigation: Water flows in narrow furrows made in the field.
- Border strip irrigation: Water flows in strips between raised ridges.
- Basin irrigation: Water is contained in enclosed basins and allowed to infiltrate the soil.

2. Sprinkler Irrigation:
- Overhead sprinklers: Water is sprayed into the air and falls like rain.

3. Drip Irrigation:
- Emitters deliver water directly to the base of plants.

4. Subsurface Irrigation:
- Buried pipes or perforated channels deliver water directly to the root zone.