This article written with contributions from Ruth Beck and Rhoda Burrows.
The flooding along the Missouri River and a few other areas last summer covered some lawn and garden areas. In many cases what was left behind looks like dirty snow. This is salt. These salts are similar to table salt or Epsom salt and are found naturally in all soils. The flood waters didn’t deposit these salts on your lawn or garden. After the flood waters receded, the water table or ground water was still near the soil surface. As evaporation took place the ground water was drawn to the soil surface carrying salts along with it. As the water evaporated from the soil, it left the salts that were contained in the water.
Salts in high concentrations are detrimental for seed germination and plant growth. Salt can limit the water that moves into the seed or the plant. In most cases, tilling the soil 4-6 inches deep and incorporating these salts will dilute their concentration so as not to affect plant growth.
If there is a concern, start with a soil sample in the affected areas. Obtain a soil probe from an extension office, garden supply store, fertilizer outlet, or NRCS office. Probe to a depth of 6 inches, and cut the soil core into 0-2, 2-4 and 4-6 inch segments. Put each segment into a separate labeled container. Take about 15 cores in the affected area, keeping each depth core separate. When finished there should be three separate samples (0-2, 2-4 and 4-6 inch) each containing 15 segments. There is no need to dry the sample. Put each segment sample into a labeled bag for soil testing. Request the laboratory run soluble salts, pH and a SAR (sodium) analysis on your samples. Also request an interpretation of the results with any remediation suggestions.
Last week soil samples were taken from 4 sites in the Pierre/Fort Pierre area. The sites were all next to the river. Samples were analyzed at SDSU and the results showed that all the soils had high levels of salt accumulations on the soil surface. The salt concentration decreased with depth. The salts in the samples that were taken appeared to be calcium carbonate (commonly known as lime). In some situations sodium could occur. This is one reason for the soil sampling recommendation. Sodium has more damaging effects and the recommendations would be different if high levels of sodium were accumulating on the soil surface.
If salts are somewhat higher than desirable and if your soil drains well and your water supply is low in salts and sodium, over watering can lower surface soil salts. Apply 6 to 8 inches of water as quickly as the soil can absorb it. That should move the salts below the root zones of many garden and lawn plants. Once the soil dries, it should be ready for seeding. One method of ensuring that the salts do not resurface is to broadcast winter wheat onto the soil surface prior to raking the land level. The addition of water to move the salts down into the soil profile will also allow the winter wheat to germinate. The winter wheat will then utilize the water, keeping it in cycle, and reducing the chance that it will accumulate on the surface again (either in your yard or and protect the soil surface from erosion. Winter wheat will not tend to produce any seed when seeded at this time of year. Mowing it as one would with any turf will also keep it vegetative. This process may be especially helpful if a person is choosing to reestablish their turf at a time later in the summer (May for warm season grass and late August for cool season grass). The winter wheat can be mowed before seeding the grass seed. The seed can then be broadcast directly into the winter wheat. The winter wheat will act as living mulch to the germinating grass. The winter wheat should not be a problem as the turf establishes itself, it will want to produce seed after the winter but at that point mowing the turf should prevent that process.
Salts accumulate during periods of excess water. Keeping plants growing on a soil surface reduces the accumulation of salts, keeping these naturally occurring salts distributed throughout the soil horizon. “Soil is meant to be covered.”