Gardening Technique Unit Screen//v.1

Soil salts are soluble minerals. They include table salt (sodium chloride) as well as salts of calcium, magnesium, and potassium. Salty soil occurs mainly in arid regions where there is not enough rainfall to wash the salts from the soil. Soil salts originate from several sources. As soil minerals weather, they slowly break down into salts that dissolve in the soil water. Irrigation water that contains dissolved salts contributes to soil salinity, and so do fertilizers. As water evaporates from the surface it moves up through the soil, bringing dissolved salts up into the topsoil. Salts may accumulate in poorly drained soils because rainfall and irrigation water cannot drain through and leach the soil. Roadside soil may become very saline in areas where de-icing salts are used in the winter. Salty soil may develop a white crust of salt deposits on the surface. Most garden plants will not tolerate much salt in the soil. For more information about plant reactions to salt, see Salt Damage.

Removing salts: Leach salty soils periodically by watering them deeply. About 12 inches of water are needed to remove most of the salts in a foot of soil. If soil salinity is a result of poor drainage, improve the soil drainage. (For information on drainage, see Soil Types, Soil Structure, and Groundwater.) The use of mulches in arid regions destroys the soil structure and causes clay particles to become lodged in soil pores, making the soil impermeable to water. Water puddles on sodic soils, and usually evaporates before it enters the soil. Some of the sodium forms caustic soda (sodium hydroxide), which dissolves organic matter. The organic substances in solution are dark brown or black. A black crust often forms on sodic soils. Sodic soils are often very alkaline, and usually do not support plant growth. To improve sodic soils, add gypsum at a rate of 5 pounds to every 100 square feet. Cultivate the gypsum into the soil, then water it well to leach the sodium from the soil. If drainage is only slightly improved, add more gypsum.

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