Probably one of the oldest methods of irrigating paddocks is surface irrigation (also known as flood or furrow irrigation), where farmers flow water down small trenches running through their crops.
Human’s first invention after learning how to grow plants from seeds was probably a bucket to carry water to plants. For most of human history, people did not have mechanized spray irrigation systems to apply water to crop fields and relied on gravity, the slope of the land and human muscle power to get water to their crops.
Surface irrigation is still used today throughout the world, especially in less-developed areas where mechanical techniques are not available. In fact, even in the United States in 2000, more land (about 29.4 million acres) was irrigated by flood irrigation as compared to about 28.3 million acres irrigated by spray irrigation.
Flood irrigation is not the most efficient irrigation method, but it is relatively cheap and low-tech. On the one hand, less water is lost to evaporation than in spray irrigation because water is applied in flowing streams rather than fine droplets, but on the other hand, more water can be lost from runoff at the edges of the fields or from over-application.
Some more efficient surface-irrigation techniques that farmers use are:
Levelling of fields: Flood irrigation uses gravity to transport water, and, since water flows downhill, it will miss a part of the field that is on a hill, even a small hill.
Some farmers use leveling equipment, some of which is guided by a laser beam, to scrape a field flat before planting. That allows water to flow evenly throughout the fields. Unfortunately, unless the levelling process is well-managed, topsoil can easily be lost and take a long time to rebuild.
Other more efficient surface-irrigation techniques that farmers use are:
Surge flooding: While traditional flooding methods involved just releasing water onto a field, using surge flooding, water is released at prearranged intervals, based on moisture status of the soil hence reducing unwanted runoff.
Capture and reuse of runoff: A large amount of flood-irrigation water is wasted because it runs off the edges and the end of the paddocks. For improved efficiency, farmers can capture this runoff in ponds and pump it back up to the water release point of the paddock, where it is reused for the next cycle of irrigation.
In this crop photo, crop rows are established on planned grades and lengths to manage the rate of runoff from both rainfall and irrigation events from surface irrigation
