Bioremediation of Saline Seeps
Objectives of this project include:
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.
4) Demonstrate an inexpensive method for tracking salinity and flow patterns around seep areas.
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.
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 two 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).
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 percent of the up-slope area should be converted to alfalfa on the five demonstration sites to cut seep recharge by 50 percent. If 100 percent of the recharge area were converted to alfalfa, 83 to 99 percent less water would enter the seep. Thus, we think at least one-third of the up-slope recharge area should be converted to alfalfa; more should reclaim the seep faster.
The economic feasibility (net return per acre) of producing switch grass (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.
More than 100 farmers attended field tours in each county at project sites. In just the second year after establishment, tour attendees witnessed greener alfalfa just up-slope 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.
For more information:
Biological and Agricultural Engineering
Kansas State University
147 Seaton Hall
Manhattan, KS 66506-2906