This article is written by Dr. Jason Warren, OSU Soil and Water Conservation State Extension Specialist.
The drought has caused numerous negative impacts on Agriculture in Oklahoma. However its impact on our ability to renovate some types of Saline and/or Sodic soils has been a positive. Saline and sodic seeps are referred to by many names, including: salt spots, alkaline spots or slick spots. They are all similar in that they contain excessive amounts of salt or sodium that prevent plant growth. However there are various differences that influence how we renovate these sites.
These areas are classified by the amount and type of salt present. Saline soils are those that contain an EC greater than 4000 μmhos/cm and less than 15% Exchangeable sodium. A Saline/sodic soil contains an EC greater than 4000 μmhos/cm and greater than 15% exchangeable sodium. Lastly, the Sodic soils contain less than 4000 μmhos/cm and greater than 15% exchangeable sodium. Given these differences it is important to have soils from these barren areas tested before a renovation plan is developed. The soil tests will provide recommendations for renovation and more detail on these strategies can be found in factsheet PSS-2226.
Beyond the classifications briefly mentioned above there are different ways in which these saline and sodic soils form. Some of these soils are formed from parent material that contained excessive salt or sodium. Others are formed when ground water moves to the surface through evaporation and deposits salt as the water is lost to the atmosphere. The drought conditions we are current experiencing can impact our ability to renovate the latter.
Figure 1: The upper picture was taken in Feb. 2011 and the bottom picture was taken in April 2013.
Hydraulic seeps, those formed from the movement of groundwater to the surface, are often found in low lying areas of the landscape where the groundwater is close enough to the soil surface that water can be conducted through capillary force to the soil surface. These forces are similar to those that allow use to suck water up through a straw but in the case of a saline seep evaporation from the soil surface provides the hydraulic gradient that pulls water from the water table. The drought has caused the water table in many areas to subside and become too deep for these force to pull water to the surface and deposit salts.
Figure 1 shows a saline/sodic soil in 2011 and again in 2013. This site had been treated with Gypsum as described factsheet PSS -2226 in 2007. However, because of a shallow water table that persisted until the onset of drought in 2011 the renovation effort was not successful because there was insufficient movement of water through the profile to leach the salts down out of the soil surface. These soils are in proximity to Stillwater Creek and Lake Carl Blackwell. The water table has declined which allows limited rainfall experienced at this site in 2012-13 to move the salts down out of the soil surface. This in turn has allowed crop establishment further improves water infiltration by protecting the soil from crusting.
The drop in most water tables across Oklahoma, particularly western Oklahoma where these salt spots are most common, provides for a unique opportunity to renovate hydraulic salt spots. Again the first course of action is to collect a soil sample to determine what types of salts are present. You can also make an effort to determine how the salt spot was formed. This information can be found on the soil survey at http://websoilsurvey.sc.egov.usda.gov/App/HomePage.htm. Your county extension educator or local NRCS can help to interpret this information.
We have observed that our success in renovating a hydraulic seep near Stillwater was greatly improved during this period of drought. However, given the fact that our sub soils are generally dry throughout Oklahoma, which improves our ability to leach salts, the drought should improve our ability to renovate those formed from parent material as well.