Bioremediation of Saline Seeps

View the project final report

• 1996 annual report

Commodities

• Agronomic: safflower, sunflower, wheat, grass (misc. perennial), hay
• Additional Plants: native plants

Practices

• Animal Production: feed/forage
• Crop Production: continuous cropping, double cropping
• Education and Training: demonstration, display, extension, on-farm/ranch research
• Farm Business Management: feasibility study
• Soil Management: soil quality/health

[Note to online version: The report for this project includes tables and appendices that could not be included here. The regional SARE office will mail a hard copy of the entire report at your request. Just contact North Central SARE at (402) 472-7081 or ncrsare@unl.edu.]

Background. Saline seeps are an increasing concern in the dryland crop production areas of Kansas. Locally known as “alkalai spots” or “slick spots”, saline seeps are areas of bare soil or reduced crop production usually located on hillsides and ranging in size from a few square yards to tens of acres. Seep development in this region is probably related to the shift from native grass prairie to annually cropped winter wheat. Wheat uses less water than native grass. The water not used by the crop moves downward through the soil. In sites susceptible to saline seeps, the water typically encounters a soil layer that directs it to a surface seep downslope from where it entered the soil. In the seep, water evaporates and leaves behind salts that were picked up along the way. Saline seeps typically go unnoticed for many years until salt concentration in the topsoil decreases crop production, which in turn leads to soil erosion problems. Normal crop production is possible in reclaimed saline seeps. Farming practices and crops can be modified to use water productively before it moves below the root zone or toward the seep.

Basically, we need to shut off the faucet feeding the seep to allow it to heal. We can do this by growing crops that use more water but still give the farmers a comparable profit.

Objectives. (1) Demonstrate several practices for utilizing soil water while it is still a relatively non-saline resource in the seep recharge area. (2) Determine crops and management practices that can sustainably control seeps. (3) Educate farmers about causes and potential solutions.

1. Demonstration. Five demonstration sites in two counties were identified for this project through cooperation of K-State Extension, Natural Resources Conservation Service, and Soil and Water Conservation District personnel. A database of surface and profile soil salinity of both seep and recharge areas at each site was developed and analyzed using computer geographic information system software. Three of five sites implemented alfalfa or native grass. After just 2 years, there already was evidence of saline seeps receding at the one site that fully implemented project recommendations. By comparison, saline seep severity increased in the two sites that did not implement alternative high-water-use cropping systems and the two sites that had existing alfalfa or native grass but in the wrong location (i.e., not in the recharge area).

2. Research. A hydrologic model was developed to help farmers determine how much land must be converted from current wheat cropping to alfalfa in order to control and remediate the saline seep. We estimated that 14 to 32% of the upslope area should be converted to alfalfa on the five demonstration sites to cut seep recharge by 50%. If 100% of the recharge area were converted to alfalfa, 83 to 99% less water would enter the seep. Thus, we think at least one-third of the upslope recharge area should be converted to alfalfa; more should reclaim the seep faster.

The economic feasibility (net return per acre) of producing switchgrass (potential bioenergy crop) was compared to continuously cropped winter wheat and alfalfa. At this time, more favorable economics (larger acreages, higher competing energy prices) are needed for competitive production of bioenergy crops. However alfalfa, one of the better crops for saline seep reclamation, was an economically competitive cropping alternative to wheat in this area.

3. Education. More than a hundred farmers attended field tours in each county at project sites. In just the 2nd year after establishment, tour attendees witnessed greener alfalfa just upslope of one seep, supporting our claim that the alfalfa was using the seep water before it could reach the “alkali spot”. This provided a good preliminary indication that we were controlling saline seep expansion while reducing erosion and growing profitable crops!

The goal of this project was to demonstrate the feasibility of using deep-rooted, high water-use vegetation to return areas with saline seep damage to sustainable farm production. The specific project objectives were to:

1. Demonstrate that control of up-gradient subsurface flow using deep-rooted vegetation is a practical and effective method for arresting and controlling saline seep damage.
• Rationale: Bioremediation of this type has been applied to saline seeps in Australia as well as the Northern and Southern Great Plains. Research recommendations and farm experience is currently available, but must be applied to site-specific conditions in south-central Kansas, where hydro-geologic conditions that form saline seeps are common. Use of bioremediation methods could return large acreages to sustainable crop production.

2. Determine which management practices, crops, and rotations are suited for saline seep remediation.
• Rationale: Saline seeps were unknowingly initiated in south-central Kansas when native grass prairies were replaced by agricultural crops about a century ago. It is now known that the reduced water use of traditional crop production practices is directly responsible for current saline seep development. Remedy of this situation will require appropriate selection of crops and flexible management practices to provide farmers with practical, economic, and sustainable options for saline seep control. Experience from other regions must be applied to local climatic and hydro-geologic conditions in south-central Kansas.

3. Educate local farmers about the causes of saline seeps, and the solutions that are available to arrest saline seeps and return affected areas to production.
• Rationale: Currently there is a general misunderstanding in the farm community about both the causes and remedies for areas with high soil salinity from saline seeps. Though most farmers in these areas can readily identify the problem areas (commonly called alkali spots or slick spots), few know the source of the problem or an appropriate treatment. Recommendations range from doing nothing to the addition of gypsum. These demonstration sites serve to help local farmers correctly identify saline seeps, increase their recognition of conditions which lead to saline seeps, and educate them about management practices to remediate these sites.

4. Develop and demonstrate the electrical conductivity approach to identifying and mapping saline seeps and potential recharge areas.
• Rationale: Use of this method could greatly increase the effectiveness and reduce the cost of implementing a seep control treatment. A simple and inexpensive method has been developed for mapping salinity gradients in the soil profile. Recommendations based on experience with local soils and subsurface water conditions could allow future crop consultants or consulting engineers to more accurately assess the size of the saline seep area as well as the direction of saline recharge (which may not necessarily follow surface topography). This information is essential for sizing and locating bioremediation treatments.