High salinity soils take special considerations to raise alfalfa

Applying water to soil is about as simple as it comes.

Sometimes Mother Nature doesn’t play nice and farmers have to find a way to get the needed moisture in the soil to raise an alfalfa crop. On the High Plains, farmers have turned to irrigation for more than half a century.

Even with all the good it brings, irrigation does have some downfalls. One issue created by irrigation is the possible increase in salinity soils. For a high dollar crop like alfalfa, it’s been a battle. Alfalfa doesn’t really care for high salinity.

In some areas of the western United States, from the Dakotas into the Southwest saline soils occur. Don Miller, director of product development, Alforex Seeds, said in his research, he’s found there’s been yield reductions because of salinity on an estimated 30% of all irrigated land in the U.S.

“Typical yield loss estimates due to salinity in salt affected regions are generally in the range of 25%,” Miller said. “It is estimated that the U.S. loses about 7.4 acres per day to soil salinization.”

Saline soils may result from high water tables that bring salts to the surface (saline seeps), or in arid climates where salts may accumulate on the surface due to irrigation or high evaporation rates. Some saline soils are so severe that comprehensive soil and water management solutions are needed to reclaim them; however there is a significant amount of farmland in the U.S. that is classified as marginally saline.

Salt tolerance

Not all hope is lost as there can be some improvement on marginal saline soils where salt-tolerant alfalfas can make an impact with proper management.

“Farmers in those affected areas often see portions of their fields that are less productive due to the buildup of salt,” he said. “Depending on the severity of the salt problem, yield losses may be seen in several forms.”

In more severe parts of a field, Miller calls them “salt hot spots” where there could be poor germination with a less than optimal stand establishment. While in other areas, yield losses can occur.

“Improved alfalfa salt tolerant varieties are unlikely to be highly productive on the most severe saline soils,” Miller said.

The varieties can be beneficial on marginally saline soils in the following ways:

• Improved germination in “saline hot spots” within existing production fields resulting in better stands. Eliminating these dead spots increases the amount of productive land on the farm.

• Improved yields on marginal saline ground.

• Genetic salt tolerance provides a new tool to combine with soil and water management in an integrated approach of reclaiming saline soils and saline seeps.

“An often overlooked benefit of new salt tolerant alfalfas is that due to their strong genetic background, they also have the genetic flexibility to produce top yields in non-saline soils as well as having the added benefit of salt tolerance to perform on marginal saline soils,” Miller said.

Breeding for it

In Miller’s viewpoint, there are two very important factors in developing alfalfa’s salt tolerance—germination and mature plant tolerance.

“The first obstacle to overcome was to select plants that could germinate in saline soils,” he said. “This was done by exposing the seed of our best varietal lines to increasing levels of salinity at germination.”

Those salt tolerant seeds that germinated were collected and crossed together, and the process was repeated for multiple generations.

“Each generation the saline improved seed was exposed to increasing levels of salinity,” Miller said. “Eventually an improved alfalfa line was developed that could germinate in half the concentration of sea water. The first variety release had only this salinity improvement for germination.”

The next step of improvement was to enhance the salt tolerance and forage production of the mature plant.

“To do this the improved salt germination varieties were planted and allowed to grow while being irrigated with increasing concentrations of saline water,” Miller said. “The most productive salt tolerant plants were selected over several generations. The newest saline tolerant varieties have this dual trait of both germination and improved forage production in mature plants under saline stress.”

Over time these improvements increased the threshold of saline tolerance in alfalfa to higher levels beyond normal alfalfa, and the improvements have been beneficial in marginal saline areas. First by improving stands in “saline hot spot” areas within alfalfa fields, and by also increasing forage yield with mature plant salt tolerance.

“This combined approach has resulted in forage yield improvements in those saline variable areas of the fields, which supported growth, but suffered varying degrees of yield losses due to saline stress,” Miller said.

Alfalfa breeders aren’t single trait selecting, but instead maintaining all the other desirable genetic traits in addition to the salt tolerance, he said.

“A successful variety, in addition to salt tolerance, must be adapted to the climate, have an adequate winter survival rating and disease and pest resistance,” Miller said. “On top of that it must not only survive in the saline environment, but still provide adequate forage yield in saline areas and still be a good yielding variety even in portions of field that are not classified as saline.”

The first factor when working on developing salt tolerance is the ability of the plants to germinate in saline soils.

“If you don’t get a stand, nothing else matters,” he said.

The second genetic factor is the ability of mature plants to produce forage under salt stress. 

“Survivability of mature plants without forage production is no advantage,” Miller said.

Management

If a farmer is facing the reality of a high salinity soil, there are a couple things to consider when trying to raise alfalfa.

“Reclaiming these saline soils is, for the most part, an integrated approach of utilizing improved genetics combined with proper soil and water management,” Miller said. “Often a severe saline soil has addition factors that must be overcome before an alfalfa salt tolerant variety can be used.”

Water infiltration is limited in some soils by sodium problems not allowing leaching of the soil salts out of the profile. Miller also said extreme pHs above 8.4 is a problem for alfalfa. He suggests the following to help remedy some of these soil issues:

—Follow soil lab recommendations;

—Improve soil structure with amendments to enhance leaching of salts out of root zone;

—Apply gypsum (provides calcium in high pH soils);

—Apply sulfur (lowers pH to free up calcium); and

—Manure or organic matter (improves soil structure).

“Take advantage of alfalfa’s deep taproot and high water use in strategic plantings near saline seep to lower water table that cause saline seeps,” Miller said.

For Miller, top five things to manage alfalfa in a high salinity soil starts with determination if salinity is a limiting factor on the farm.

“Conduct a soil and water test to determine extent and severity of salinity on the farm,” he said.

Second is to have realistic expectations.

“Salt tolerant alfalfas have an improved tolerance or higher threshold to salinity, but there is an upper limit to their tolerance,” Miller said. “Soils with very high salinity levels may require an integrated approach of combining advanced genetics with soil and water management to make them productive.”

Third is to make sure salinity is really the problem, and not another performance limiting soil condition. A high pH or high sodium absorption rate greater than 13 can cause problems.

“Salt tolerance will not perform if there is a high pH level or a sodium problem,” Miller said.

Fourth is to be cognizant of seed mixtures.

“The new salt tolerant alfalfas can provide advantages in most marginal saline soils however in fields with higher salinity levels a mixture of a salt tolerant grass species with a salt tolerant alfalfa might give the widest range of protection from salinity,” Miller said.

And finally, plant on the high end of recommended seeding rates for irrigated or dryland fields to ensure optimal stands on marginal soils.

“The utilization of the marginal land is becoming more and more critical to farmers and ranchers as they try and maximize profits on the land they have available to them,” Miller said. “Salt tolerant alfalfa could have an increasing role in making less desirable farmland more profitable.”

When working to increase stands and yields on marginally saline soils, improved genetic lines can be beneficial, but they are only one part of the overall picture.

“Plant breeders are continuing to push the plant salinity threshold to higher and higher levels of tolerance with each new variety release,” Miller said. “The development of new, improved salt tolerant alfalfa varieties has given forage producers a new means of combating salinity and minimizing salinity related production losses and an opportunity to improve profits by more fully utilizing more of their farm ground.”

Kylene Scott can be reached at 620-227-1804 or [email protected].