Angel Mirae Morris, P. Jeff Maughan, Bryan G. Hopkins and Neil Hansen, Plant & Wildlife Sciences
Chenopodium quinoa is native to the Peruvian Andes and has been an important food crop for more than 5,000 years. C. quinoa can adapt to a wide variety of climates and altitudes, making it a viable food source for areas of the world that have little rainfall or experience dramatic seasonal changes in temperature. Further, according to a study conducted in 20161, quinoa was found to be extremely salt tolerant without detriment to the grain. High salinity tolerance suggests that planting quinoa may potentially improve soil conditions, however, little research has been conducted on the bioremediation effects of C. quinoa. This study explores the hypothesis that growing C. quinoa will reduce levels of salinity in soil.
Materials and Methods
To conduct the experiment, 4 groups of pots containing soil of varying salinity levels were prepared. Each group contained 2 negative control samples with no plants and 8 pots, each growing a single quinoa plant. Forty one-gallon pots each containing 2.5kg of soil were used. In order to duplicate natural conditions as closely as possible, tap water was used in lieu of distilled or purified water.
First, the salinity level of the control group was determined by calculating the electrical conductivity (EC). Thirty-five gallons of soil was sifted with a 2 mm sieve to remove debris. The soil was dried for 2 weeks. After 2 weeks, 3 samples of 50g of soil was placed in plastic cups and saturated with water for 8 hours. The water was strained from the soil and tested with a conductivity probe. The EC for the control group was .531 dS/m2. Next, the moisture content3 was calculated to be 39% and used together with the TDS equation4 to determine the amount of salt required to artificially set salinity levels. Commercial sea salt was added and the soil was mixed in a 10 cubic ft mixer. Each group was tested to confirm EC levels.
Before planting, 4 pots were randomly selected and overfilled with water to calculate field capacity5. Each group was then split into normal and drought conditions (60% field capacity). Each group contained 5 pots (4 with plants and 1 negative control). Normal conditions were watered at field capacity. Pots were weighed every other day to calculate the amount of water necessary to maintain normal or drought conditions, and then watered accordingly. Pots were organized using a randomized complete block design (RCBD). Three seeds were planted in each pot and thinned to 1 seedling after 3 weeks. After 12 weeks, the plant was removed from the pots. The soil was separated and dried for 2 weeks and the EC was retested for each pot.
Figure 1 demonstrates graphically the measures of initial soil salinity, final soil salinity, and percent change for each pot. The final salinity levels in pots containing quinoa plants were lower than initial readings. However, the negative control pots (no plants) containing soil with artificially set salinity levels also showed a decrease over the course of the experiment.
Figure 1. Initial and final dS/m. Measurements of pots before and after planting. The first pot of each group was the negative control (no plants). Groups A and B were the control group, groups C and D were set at 4 dS/m, groups E and F were set at 8 dS/m, and groups G and H were set at 16 dS/m. Groups B. D, F, and H were subject to drought conditions.
Of the 40 pots, 3 were removed as outliers. Pots C5 and H5 were excluded due to leaching of the salts when calculating field capacity. Pot E5 was removed from the study because Chenopodium album (common lambs quarters) had been mistaken for quinoa during thinning.
The increase in salinity levels in groups A and B could be due to salinity levels in the irrigation water. As expected, final salinity levels were lower in all samples except Group A and pot B1. However, salinity levels in negative control group pots also decreased. A possible explanation for this unexpected result is that during irrigation, salts in pots with no plants may have leached out of the soil whereas root systems in pots with plants may have prevented such leaching. In Groups G and H, percent change over the experiment were lower, though these groups had the highest salinity levels. The initial salinity level may have already been at or above equilibrium, causing some previously insoluble salt to be dissolved into the soil after irrigation began.
Based on the results of the study, though C. quinoa has measurable effect on soil salinity, in order to see a significant improvement, crops would have to be grown and harvested over the course of many years. The study is currently still in progress. Further research is necessary to determine if long-term cultivation is effective and to what extent. Also, further analysis, such as ICP, would be beneficial determine how soil salinity affects the quinoa plant and grain.
1 Wu G, Peterson AJ, Morris CF, Murphy KM. 2016. Quinoa Seed Quality Response to Sodium Chloride and Sodium Sulfate Salinity. Frontiers in Plant Science. 7:790.
2 Unit used for salinity measurement.
3 MC%=((W2-W3)/(W3-W1)) x 100
4 Measure of total inorganic and organic compounds in a liquid. TDS = EC x 640 x .39 (EC < 5 dS/m) TDS = EC x 800 x .39 (EC > 5 dS/m)
5 Wet weight – dry weight = amount of water for plants