Subsurface Drip Irrigation in Alfalfa
While subsurface drip irrigation as a well-known feasible alternative irrigation technology has been applied primarily for high value crops of fruits, vegetables, nuts, and sugarcane, as system reliability and longevity improved, its application has expanded to lower value agronomic crops including alfalfa. Likely less than 1% of the western alfalfa crop is currently buried drip irrigated. This system is accurately described as still in development, but a number of alfalfa growers have had success with the system.
Drip lines with a lifetime of 6 to 12 years are placed subsurface 8 to 18" (20–45 cm) below the soil surface on 30"–80" (75–200 cm) centers, depending upon soil type. Alfalfa fields would likely be rotated with another crop such as corn, wheat, cotton or tomato over a 6–12 year period, leaving the system in place, so the return on investment would be optimized.
Advantages and Disadvantages of Drip Irrigation for Alfalfa
A key benefit of SDI on alfalfa is the ability to continue irrigating immediately prior and after, even during the multiple seasonal harvests. The critical stage to meet the water needs of alfalfa is after each cutting, when the crop starts regrowth. In fact, buried drip allows irrigation to continue during or right after harvest to encourage rapid regrowth. There is no need to stop irrigation for a soil dry down period before harvest or while the hay is curing, because the water is applied below the soil surface. Particularly, greater water distribution over time and space during the growing season reduces the amount of water stress on alfalfa and causes for rapid re-growth and higher yields which is linearly related to transpiration.
Some other potential advantages are:
- Higher yield possibilities (controlled studies and grower experience).
- Ability to fertigate accurately and conserve nutrients.
- Improved oxygen availability in root zone.
- Low labor requirement for irrigation events.
- Low weed pressure due to dry surface.
Although the benefits accounted for SDI, several challenges may be noted by the system for alfalfa production. Maintenance and gopher strikes are among the challenges that for some areas could hamper the use of SDI in alfalfa. Some other potential disadvantages are:
- High investment cost.
- Water quality requirements and treatments.
- May require periodic alternative irrigation techniques (e.g. sprinklers or flood) to manage salts, distribution, and gophers.
- Difficulty in upward water movement between drip tapes on some soil types and spacing.
- Higher level of irrigation management.