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ON-FARM DEMONSTRATION STUDY:

Drip Irrigated Alfalfa

Certain irrigation systems have the potential to conserve water by eliminating tailwater. To better understand this potential, the Team has been studying the work Don Emanuelli has been doing for the past few years on a 50-acre field with a subsurface drip irrigation system. Don’s system, initially designed to irrigate vegetables, relied on drip lines spaced at 60-inch intervals and buried 8 to 10 inches deep. In the fall of 2002, Don shifted away from vegetables but opted to test the existing drip irrigation system on alfalfa.

With Don’s help, IID water records and the system’s flow-meter readings, we were able to compare per-acre yields and water use for the drip irrigated field versus a nearby row irrigated alfalfa field planted at about the same time.

Below is a quick synopsis of the results:

• The average annual per-acre yields and water use for 2003, 2004, and 2005 for row alfalfa was 8.8 tons of hay with 7.8 AF of applied water, compared to 8.3 tons of hay and a 600- pound seed crop in 2005 with 6.0 AF for drip alfalfa. If 1.5 tons of hay were substituted for the 2005 seed crop, the average drip and row yield would be the same (8.8 tons/acre); the drip irrigation conservation savings, which averaged 90 AF per year or about 1.8 AF/acre per year for the 50-acre field, would be 0.2 AF per ton of alfalfa hay.
• The drip system is operated using incidental labor, but it needs to be periodically watched and serviced. The pump engine required about 2.6 gallons of diesel per ton of alfalfa hay. The replacement cost of the 50-acre buried drip system would be about $86,000. When amortized over a 10-year cropping cycle at 6% interest, the annual fixed cost would be $232/acre, which is $26.50 per ton of hay during the alfalfa portion of the cycle.

Additional demonstration projects will be highlighted in future issues. As well, more detailed descriptions of each project will be posted on the Definite Plan webpage.