Update:
View uploaded report 
Executive Summary Report
Harvesting Soil Salts from Soybean Production Fields: Evaluating a New Method
Dr. Aaron Daigh, NDSU Soil Science Dept., Principle Investigator
Dr. Thomas DeSutter, NDSU Soil Science Dept.
The main goal of this project was to test a new method of removing salts from saline soils to improve soil health and soybean yields. We surface applied ferric hexacyanoferrate, to saline soils, which disrupts the formation of a hard salt crust and allows salt crystals to grow above the soil surface to then be easily harvested. Previous studies demonstrated the proof of concept in extremely high saline soils contaminated with sodium chloride brine solutions. This project tested the method on other salt species commonly observed in naturally occurring saline soils in North Dakota and evaluated any subsequent effects on soybean and wheat health and soil health.
In this study, sulfate based salts (calcium, sodium, and magnesium sulfates) formed a hard crust at the soil surface and did not allow salt effloresce (i.e., growth) as anticipated. In previous tests, we observed up to 60% of sodium chloride salts to effloresce above the soil surface for harvesting. We hypothesized the lack of sulfate-based salt growth was due to the low solubility of the salts as compared to sodium chloride. We then evaluated if chemical additives could be included to overcome the sulfate salt crusting issue. A variety of additives known to increase the solubility of sulfate salts were evaluated. However, such additives were also not successful. Investigating in more detail, we conclude that ferric hexacyanoferrate is limited to sodium chloride due to its physical size and geometry that initiates efflorescence and not from early crusting of other salts.
When evaluating the effects of ferric hexacyanoferrate on plant and soil health, we observed that all plant tissues (above and belowground) and soil metrics were significantly affected by the ferric hexacyanoferrate loading rate. The only exceptions were for plant root calcium concentrations and soil total fungi, eukaryotes, fungi to bacteria ratio, predator to prey ratio, monounsaturated to polyunsaturated fatty acid ratio, cation exchange capacity, and soil test Ca and Mg. Soil bacterial communities within the rhizosphere significantly decreased with loading rates. Moreover, their stress (i.e., cyclopropanes to monounsaturated fatty acids ratio) significantly increased with loading rate. In general, the soil microbial communities appear to be more sensitive (i.e., affected at lower loading rates of ferric hexacyanoferrate) than the plants.
The primary goal of this research was to modify our existing method, used for brine spills, to work on natural saline seeps and road-ditch salinity. Unfortunately, modification of our method was not successful and no clear path forward is apparent at this time. Thus, the salt harvesting method remains limited to sodium chloride brine spills. For example, fracking water spills in northern and western North Dakota. However, this research still benefits ND soybean farmers by providing insights to the impacts the method will have on soybean and wheat grown on farmlands which have been contaminated via a brine spills and then remediated with the existing method. In general, the application rates of 200 g m-2 (i.e., the recommended rates for brine spills) does not appear to significantly affect soybean and wheat performance. However, the soil microbial community does appear to be affected at all application rates. Since the ferric hexacyanoferrate increased stress levels of rhizosphere bacteria, this could mean that soybeans will endure greater stress during drought periods. Since hexacyanoferrate has a substantially slow degradation rate (i.e., hundreds to thousands of years), these microbial stress levels may also persist for a similar period.