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.In parts of Montana, saltconcentrations in soil water have reached levels double those of seawater.Besides certain salts having specific toxic effects on crops, high salt con-centrations exert a general harmful effect on crops similar to the effect of adrought, by raising the osmotic pressure of soil water and thereby making itharder for roots to absorb water by osmosis.The salty groundwater mayalso end up in wells and streams and may evaporate on the surface to leave acaked layer of salt.If you imagine yourself drinking a glass of "water" moreconcentrated than the ocean, you will appreciate that not only does it tastehorrible and prevent farmers from growing crops, but that its dissolved boron, selenium, and other toxic ingredients may be bad for your health(and for that of wildlife and your livestock).Salinization is a problem todayin many parts of the world besides the U.S., including India, Turkey, and es-pecially Australia (see Chapter 13).In the past it contributed to the declineof the world's oldest civilizations, those of Mesopotamia: salinization pro-vides a large part of the explanation for why applying the term "FertileCrescent" today to Iraq and Syria, formerly the leading center of world agri-culture, would be a cruel joke.Montana's main form of salinization is one that has ruined several mil-lion acres of cropland in the northern Great Plains as a whole, includingseveral hundred thousand acres in northern, eastern, and central Montana.The form is called "saline seep," because salty water building up in theground in an uphill area percolates through the soil to emerge as a seep in adownhill area up to half a mile or farther distant.Saline seeps frequently be-come bad for neighborly friendship when the agricultural practices of onefarmer uphill cause a saline seep on a downhill neighbor's property.Here is how a saline seep arises.Eastern Montana has lots of water-soluble salts (especially sodium, calcium, and magnesium sulfates) presentas components of the rocks and soils themselves, and also trapped in ma-rine deposits (because much of the region used to be ocean).Below the soilzone is a layer of bedrock (shale, sandstone, or coal) that has low perme-ability to water.In dry eastern Montana environments covered with nativevegetation, almost all rain that falls is promptly taken up by the vegeta-tion's roots and transpired back into the atmosphere, leaving the soil belowthe root layer dry.However, when a farmer clears the native vegetation topractice crop-and-fallow agriculture, in which an annual crop like wheat isgrown during one year and the land is left fallow the next year, there areno plant roots to take up rainwater falling in the fallow year.That rain-water accumulates in the soil, waterlogs it below the root layer, and dissolvessalts that then rise into the root zone as the water table rises.Because ofthe impermeable underlying bedrock, the salty water doesn't drain deeplyinto the ground but emerges somewhere downhill nearby as a saline seep.The result is that crops grow more poorly or not at all, both in the uphillarea where the problem arises and in the downhill area where the seepemerges.Saline seeps became widespread in much of Montana after 1940 as aconsequence of changes in agricultural practices especially the increasinguse of tractors and more efficient soil tilling devices, weed-killers to killweed plant cover during the fallow period, and more land under fallow each year.The problem must be combatted by various intensive types of farmmanagement, such as sowing salt-tolerant plants in the downhill seep areasto start reclaiming them, decreasing the length of fallow time in the uphillarea by a crop schedule known as flexible cropping, and planting alfalfa andother perennial water-demanding crops with deep roots to take up excesswater from the soil.In the areas of Montana where agriculture depends directly on rainfall,saline seeps are the main salt-related form of land damage.But they are notthe only form
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