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Saline Soils Assist

Friday, February 1, 2008
filed under: Rotation

When it comes to your ancestors, “salt of the earth” is a good thing. When it comes to your soils, not so much.

Saline soils have prehistoric roots in the Red River Valley basin of North Dakota, Minnesota and Manitoba, dating back to the existence of Lake Agassiz. The huge lake, formed thousands of years ago from the melting glacial mass that once covered the region, contained salts which, when the lake finally drained northward, stayed behind in the fertile soils. Additional salinity, especially in Grand Forks and Walsh counties of North Dakota, is the result of discharge of regional groundwater originating from further west.

Within the past century, human activity has helped uncap the saline groundwork laid by Mother Nature. Extensive drainage in the region, coupled more recently with the greatly expanded production of salt-sensitive crops like beans and corn, has resulted in more salinity problems in the Red River Valley basin. Mike Ulmer, senior soil scientist with the Natural Resources Conservation Service’s (NRCS) Bismarck, N.D., office, estimates there presently are somewhere between 1.5 to 2.5 million acres of “saline soils” in this watershed.

That’s an important figure for farmers — and obviously more so for those farmers whose operations contain saline soils. “As salinity increases in the root zone, that salt competes with the plant for water. Basically, the salt will hold the water and make it unavailable to plants,” Ulmer explains. “So your soils could be very wet — and yet the crop could, in effect, be suffering from ‘drought.’ ”

Some very productive land has been compromised as a result. Salinity has in many cases resulted in partial loss of crop yield; in some cases, virtually total loss.

Does deep tillage help alleviate salt concentration in upper soil levels? Tom Burchill, special crops coordinator with the Arthur Companies of Arthur, N.D., doubts it. “Some people think by breaking up that hardpan, you can help the problem by having better internal drainage,” he remarks. “But all the NDSU tests I’ve seen on deep tillage have shown it’s a fairly insignificant [factor].”

Ted Alme, NRCS state agronomist for North Dakota, concurs. “As an agency, we actually look at no-till and reduced-till scenarios when we get into saline conditions,” he says. “No-till would reduce compaction and, in concert with a good crop rotation, add residues and provide cover at the soil surface — which would mitigate the salinity effect.”

While virtually no crop will be productive under severe soil salinity, sunflower is among the best on slight to moderate saline soils, Alme says. “It’s a deep-rooted crop with a strong taproot that’s going to break through some of those more-restrictive layers that you normally see in a saline scenario,” he points out. “If you get the sunflower plant established, its strong root will go down and create pores for downward movement of water — which is what we’re looking for to help move those salts out of the root zone.”

Burchill, who works extensively with his company’s high-oleic sunflower program, agrees. “Sunflower and barley are, I think, the best crops to put on those types of soils.” One of Burchill’s mid-Red River Valley customers farms on some heavy, not-well-drained soil that gets quite salty. “He says he’s never raised more than 30-bushel soybeans on it; but last year he had sunflower that went over 2,000 lbs” per acre, Burchill relates.

Probably the best long-term treatment for saline soils is tile drainage. “But that’s expensive; and in some places you don’t have a good outlet” for the water, Burchill notes. On the other hand, “one of the worst thing for salty areas is to have no crop on them.” Some growers have put such ground into CRP and planted a salt-tolerant grass. “But of course, with today’s crop prices, most folks want to take ground out of CRP — not put it in,” Burchill notes.

Subsurface drainage and CRP aside, NRCS’s Mike Ulmer believes sunflower “has great potential to help us manage our saline conditions. It uses water deeper in the profile; so wherever the plant uses the water, the salts will precipitate out. You can use sunflower to lower the water table, lower where the salt zone increases — and then come back in your rotation with a shallower-rooted crop.”

— Don Lilleboe
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