Wherever alfalfa fields are irrigated or sub-irrigated, the potential for salinity exists. “Anytime water comes out of the ground it picks up salts,” said Don Miller, director of product development for Alforex Seeds. Miller presented information on salinity at all three stops of the 2017 Alfalfa U tour in Grand Island, Nebraska; Dodge City, Kansas; and Twin Falls, Idaho.
Saline, or marginal soils, refers to dissolved salts, variations in pH or sodium levels that affect the drainage of that soil. Saline soils have high levels of dissolved salts above 4 electrical conductivity, known as EC, alkaline soils have a pH above 8.5, and alkali soils have sodium levels above 15 percent.
“The more salt in water the more electrical current will pass through it,” Miller said.
Anytime soil has an EC level above 4 it is considered a saline soil. Alfalfa begins to show damage in any soil with an EC of 2 or greater. An EC level of 3.4 could reduce alfalfa production by 10 percent. An EC level of 8.8 could reduce alfalfa production by 50 percent. That is across the field and not just in the visible hot spots.
If a producer irrigates, he should be aware of the water quality and water source. Water from wells, reservoirs or rivers can all have different salt levels.
Applying manure to crop ground also may add salt to the soil. The manure from one dairy cow can add 4 pounds of salt per day.
Alfalfa producers need to measure soils to determine salinity level and also measure salt content in irrigation water.
One way to manage saline soils is to look at the species planted on that field. Different crops have different salt tolerance levels. Only use a crop species tolerant to the level of salinity. Miller said as soil improves with integrated soil and water management, growers can move to higher value, more tolerant crops.
Improving the absorption rate of the soil can improve the salinity level. Poor soil structure and poor water infiltration can lead to less leaching of salts out of the soil profile.
Alforex has developed salt tolerant alfalfa varieties such as PGI 427 and Rugged. Improved varieties can provide better stand establishment and better yield on marginal ground, but Miller said growers should have realistic expectations.
An integrated approach that includes soil and water management along with improved alfalfa varieties is the best way to manage salinity.
Doug Rich can be reached at 785-749-5304 or firstname.lastname@example.org.