In a time when sustainability is on the minds of many, farmers are wondering if they will have enough water to care for their crops. So, researchers at New Mexico State University’s Agricultural Science Center at Tucumcari are working on an alfalfa project to see if an irrigation termination system will maximize yield at the end of the growing season – a tool to use only if water is scarce.

Alfalfa is New Mexico’s No. 1 cash crop, bringing in an estimated $238 million to farmers in 2008, but producers are still at the mercy of water availability, a crucial factor in a state known for drought.

“New Mexico currently cannot produce enough alfalfa to meet our own needs due to limited water for irrigation,” said Leonard Lauriault, forage agronomist at the Tucumcari center. “The focus of this study is to determine which cuttings a producer can forego irrigating if irrigation water is short.”

In a collaborative project with Sangu Angadi, a crop stress physiologist at the Agricultural Science Center at Clovis, Lauriault is looking at the effects – above and below the ground – that termination treatment has on alfalfa. The results of the three-year study are encouraging.

At Tucumcari, researchers are measuring the yields of different plots of alfalfa, each with a different irrigation termination schedule on two different varieties of alfalfa, Wilson and New Mexico Common. The varieties are similar to each other, but Wilson was developed to withstand less than optimum soil moisture conditions. Eight different irrigation treatments are used on the alfalfa. Furrow irrigations were applied to each of six harvests, or to various combinations of the six harvests.

The researchers discovered that it is possible to not irrigate alfalfa for a selected cutting and still get a high annual yield.

“Based on data collected so far, producers can afford to skip irrigation on one cutting during late summer or fall without experiencing a significant reduction in annual yield,” Lauriault said. “If it is known that irrigation water will be short, it is best to irrigate the first three cuttings well to maximize yield. Additionally, based on other research at Tucumcari, whether or not irrigation water is short, if a warm spring is forecast, producers can significantly increase yield of the first and maybe second harvest by beginning irrigation before typical spring green up.”

Any more than one irrigation cut, Lauriault said, and the farmer risks taking a hit on the yield.

Depending on the area of the state, producers can harvest between three and seven cuttings each season from their alfalfa. Lauriault said that by skipping one irrigation treatment at the end of the growing season, when the alfalfa does not grow as fast in preparation for winter, producers do not risk losing their yield as the crop growth is already slowing down.

If producers do not irrigate their last cutting, they can save between six and eight inches of water.

So how can farmers maximize water available to grow a healthy alfalfa crop?

Lauriault advised producers to wait until they have canopy closure – when the ground is completely shaded by alfalfa – to irrigate their fields in an effort to limit the chance for weed seedlings to grow and survive.

He also cautioned producers not to over-irrigate and prevent runoff. The first irrigation can be applied before spring green-up, which is a good time for farmers to begin building up the soil moisture profile. Maintaining the profile during spring and early summer will maximize yield at that time and establish a reserve for mid- and late summer when irrigation and soil water infiltration capacities cannot meet the alfalfa’s needs. When it is time for the first cutting, the top of the soil will be dry to allow for harvesting, but the deeply rooted alfalfa can access the moisture well below the surface and is healthy. By keeping the top few inches of the field dry, farmers have an easier time cutting.

If farmer know they have a limited amount of water to work with, Lauriault said they should not stretch the water over the entire season, but concentrate on irrigating the first cuttings to get more yield of the early crop. Essentially, they should water, he said, as though they are not facing a shortage. When the water runs out, the alfalfa’s deep roots and ability to go dormant will help it take care of itself. When the alfalfa goes dormant due to drought, six inches of stubble with leaves should be left in the field whenever it is harvested to allow the alfalfa to continue making its own energy.

Lauriault advised producers to irrigate alfalfa as soon as water is available, as it will take the crop another cutting before it recovers from irrigation termination.

Researchers have seen consistent results each year since they started the termination treatment study in 2006 on an alfalfa crop planted in late summer of 2005. The next phase is to take a closer look at fall and winter irrigation termination techniques. Angadi is measuring soil moisture level and runoff and other aspects of crop stress physiology of the alfalfa.