Brackish Water is Toxic To Crop Plants
About 97% of the fresh water on the earth is considered too brackish (too salty) for most agricultural use. Desalination, or purification, is of course possible. Mechanical desalination processes are widely known. But making desalination cost effective and environmentally friendly can be challenging. The National Acadamies tell us that desalination research is needed. This message has been repeated for decades.
Several years ago, my colleagues and I observed the ability of fungal endophytes to confer salt tolerance to crop plants. We were told by our agency higher-ups to halt the research because it fell outside our mission area. Later, David Johnson of New Mexico State University reported fungal communities in bioactive composts that were capable of desalination.
Surprisingly, federally funded research into biological desalination processes progresses at a snail’s pace. This is not because breakthroughs are few and far between. Rather, it is because there are so many bacteria, fungi, and other microbes with potential for desalination that standardizing processes to fit industry is challenging.
The good news is, biological desalination at small scales is quite feasible and affordable, if you are willing to do a little experimentation. Here, we demonstrate a simple trial we ran that demonstrates biological processes any grower can leverage to help plants grow well in saline water.
Commercial Biostimulants Can Boost Plant Growth. Which Ones Work In Brackish Water?
Biostimulants are additives that boost plant productivity, but lack the macronutrients necessary to label them as fertilizer. Often organic, biostimulants support plant growth any time critical plant hormones, plant and soil microbes, or trace elements are missing. Biostimulants can add resilience during heat waves or cold spells, and they can alleviate stress caused by drought, salinity, pests, or other factors.
Knowing which biostimulant to add, and when to add it can be difficult. Because every growing environment is different, practices that work well for one grower may not give the same result in another location or on a different crop. The biostimulant industry is struggling to create standards and labeling rules that make it easy for consumers to know which formula will work best for them. In the meanwhile, simple tests like the one outlined below can be used by any grower to identify which biostimulants will work under their own growing conditions.
This test was motivated by our own curiousity regarding two commercial biostimulants, discussed below.
Bloomin Minerals and Symbiosis AgX were the Commercial Biostimulants Tested
We wanted to find solutions we could recommend to beginning gardeners who deal with brackish water. Brackish water is not uncommon in Southern New Mexico.
Since first time gardeners are dealing with steep learning curves, we explored ready made preparations. We began with Bloomin Minerals, which is a high quality humate with a rich blend of trace minerals. Bloomin Minerals is available in garden scale volumes through our affiliated online store. We have already had good success with Bloomin Minerals in other applications. However, many of the gardeners we are dealing with use container gardens filled with commercial garden soil. Since commercial garden soils are already rich in humates, and presumably rich in nutrients, we wondered if Bloomin Minerals would have any effect on plants growing in such a rich medium.
We knew from prior testing that the commercial garden soil was low in microbial diversity and abundance, but we also knew that most beginning gardeners won’t set up a bioreactor and start making compost. Since we have not had good luck with commercial fungal preparations, we opted to add microbes using a bacterial rich biostimulant called Symbiosis AgX. While we currently have no commercial affiliation with Symbiosis AgX, we have tested the product in other applications and seen good results.
Since we could not find recommendations for growing container gardens with brackish water, we set up a small experiment.
The goals of the experiment were:
- to evaluate the effects of commercial biostimulants on container grown, cool season vegetables irrigated with brackish, chlorinated tap water.
- to compare the additive effects of biostimulants with different modes of actions.
- to demonstrate the value of grower led, on site experiments to guide grower decisions.
Setting Up the Experiment
Study date and location:
The experiment was run in Dona Ana County, approximately 6 miles east of Vado, New Mexico. The elevation was 3900 feet. Planting was carried out on September 2, 2019. Final observations were recorded on October 31, 2019.
What Was Done:
Four treatment groups were established in containers assembled as described previously. Expert Gardener Organic Garden Soil, was used as the growing medium. This soil, and the bucket containers were purchased from a local Wal-Mart. 3 replicates were established for each treatment. Snap peas (Pisum sativum var. Sugar Daddy) were chosen for this test because they grow quickly and tolerate the shorter days and cooler weather of the fall season. As edible legumes, snap peas are popular additions to home vegetable gardens.
Planting procedures varied by treatment as follows:
- Group 1-Control. 12 seeds were placed in zipper-locking sandwich bags with 1 ounce (30 mL) of RO water and refrigerated overnight. The following day, seeds were buried to a depth of 1 inch in containers, with 4 seeds to a container. An inch of preconditioned straw mulch was used to cover the soil, and the bucket was irrigated with tap water until the soil was saturated. Excess water was allowed to drain through the holes at the bottom of the buckets.
- Group 2- Bloomin Minerals Treatment (aka Bio 1) . One forth cup (~60 mL) of Bloomin Minerals was added to each 5 gallon container and mixed into the top 12 inches of soil. Meanwhile, 12 seeds were placed in zipper bags with with 1 ounce (30 mL) of RO water and 1/8 teaspon (0.6 mL) of Bloomin Minerals granules. The seeds were refrigerated overnight. The next day, seeds were planted, mulched, and irrigated as described above.
- Group 3 -Ag X Treatment (aka Bio 2). The Symbiosis AgX was diluted in RO water to the manufacturer’s specifications. One ounce (30 mL) of biostimulant was placed in a zipper bag with 12 seeds and refrigerated overnight. Seeds were planted the next day, mulched, and irrigated as described above. After irrigation, one quart of the diluted commercial biostimulant was sprinkled on each bucket. Two weeks later, a second treatment was applied. Again, one quart of diluted biostimulant was applied to each bucket.
- Group 4 -Bloomin Minerals Plus AgX (aka Bio 1+2). One forth cup (~ 60 mL) of Bloomin Minerals was added to each 5 gallon container and encorporated into the top 12 inches of soil. The commercial biostimulant was diluted in RO water to the manufacturer’s specifications. One ounce (30 mL) of biostimulant was placed in a zipper bag with 12 seeds and 1/8 teaspon (0.6 mL) of Bloomin Minerals granules. The mixture was refrigerated overnight. Seeds were planted the next day, mulched, and irrigated as above. In addition, one quart of diluted biostimulant was applied as for Group 3. Two weeks later, a second biostimulant treatment was applied as above.
Water Quality and Irrigation
Tap water had a pH of 7.7 as determined by handheld digital pH meter, and an EC of 2430 μS/cm, as determined by a handheld, digital conductivity and TDS meter.
For the first week after planting, seedlings were checked daily for moisture in the top 1/4 inch of soil. When dry, plants were irrigated by sprinkling a quart of tap water on the surface. As seedlings emerged and developed longer roots, irrigation was delayed until the top inch of soil was dry to the touch. Then soil was heavily irrigated.
Days to Emergence
Days to emergence were estimated by counting the number of seedlings visible at days 3 and 9.
Nutritional status was estimated by measuring leaf Brix values with a refractometer which had been calibrated to a 15% sugar solution. Six leaves were removed from randomly selected plants in the Bio 1+2 treatment, and crushed with a garlic press to extract sap. Sap droplets were placed on the refractometer lens, and read immediately.
Plants from the remaining treatments did not have enough leaves for meaningful sap extraction. Therefore, the leaves from the three treatments were pooled and sap was extracted for Brix determination.
Seeds treated with Bio 2 were the only seedlings to emerge above the soil by day 3. The Bio 2 treated seeds germinated quickly whether Bio 1 was present or absent (Table 1).
No new seedlings emerged after day 9. Some seedlings from the Bio 1 treatment were observed, but not counted, between days 3 and 9. These seedlings were missing on day 9. These may have been eaten by a bird or rodent.
The plants treated with microbial based biostimulant (Bio 2) showed slightly more green, and larger leaves than either the control or the Bio 1. Bio 1 + 2 treated plants exhibited vigorous growth throughout the experiment, with open flowers visible by day 54 (not shown). Brix readings taken on day 54 gave a value of 7.8 for the Bio 1+2 treatment, and a value of 7.0 for the pooled samples. Sub-freezing temperatures on the evening of day 59 brought the experiment to an end.
|Table 1. Number of seedlings visible at 3 and 9 days after planting.|
|Treatment||Day 3||Day 9|
|Bio 1 + 2||6||10|
Figure 2, below, shows representative leaf samples from each treatment after 36 days. Stunted growth and chlorosis (yellowing) was problematic, particularly for Control, Bio 1, and Bio 2 treatments. Figure 3 shows whole plants on day 55. Note the difference in size, color, and development between the Bio 1+2 treated plants and the remaining treatments.
Figure 3. 55 day old pea plants, Pisum sativum var. Sugar Daddy, grown in alkaline water. Plants treated with Bio 1 (blue flags), Bio 2 (green buckets), and untreated plants (control, far right) suffered stunted growth and chlorosis, Bio 2 plants exhibited more green leaves, and larger leaves, than either Bio 1 or the control. Plants treated with Bio 1 + 2 (yellow buckets, left) exhibited normal growth. No stunting or chlorosis was evident.
Interpreting the Results
Insights gained from this simple experiment are summarized below.
Peas don’t like hard, alkaline water.
The overall growth of the Pisum sativum var. Sugar Daddy (pea plants) in the container gardens was poor for all treatments except the Bio 1+2 paired biostimulants. The most likely cause for the chlorotic coloring and stunted growth was the quality of the irrigation water, as indicated by an EC value of 2430 µS/cm and a pH of 7.7. Such brackish, alkaline water can interfere with osmotic balance and impede plant nutrient uptake.
Humates alone won’t overcome the salt problem.
Plants grown in the presence of the Bloomin Minerals (Bio 1) in the absense of Ag X (Bio 2) did not perform well. Visual inspection of leafs (Figure 2) and whole plants (Figure 3) revealed plants slightly more stunted than the controls. The low number of emerged seedlings (Table 1) is not likely due to a treatment effect. Seedlings that were visible prior to day 9 disappeared after emergence.
The low number of emerged seedlings in Bio 1 treatment is not likely due to the Bio 1 treatment.
Table 1 indicates only 4 seeds were present in at day 9. Since seedlings that were observed during daily inspections were missing on day 9, it can be assumed that these and other missing seedlings may have been eaten by birds or rodents. For this reason, no claims can be made about treatment effects on successful plant emergence.
The microbes in Bio 2 could not overcome the salt problem.
The seeds treated with Bio 2 germinated earlier than other treatments, regardless of whether Bio 1 was present. Plants treated with Bio 2 alone were also slightly greener than the control plants, with fewer burned leaf margins, particularly in last 10 days of the study. Nonetheless, performance was unimpressive, and salt damage was evident.
Bio 1+2 treatments produced robust, vigorous plants with Brix readings typical of fresh market produce.
The combination of both biostimulants in the Bio 1+2 treatment produced vigorous plants with flowers within 55 days. Since the variety is listed as reaching maturity within 50-70 days, the plants were well within the expected range despite the brackish water. The Brix reading near 8 places the plants at a threshold above common supermarket produce, though still below the ideal value of 12 sought by many in the eco-agriculture arena. Brackish water reduces nutrient uptake in both plant and microbial cells. It may be that the trace minerals added by the Bio 1 (Bloomin Minerals) was necessary in order for the organisms applied with Bio 2 to overcome the negative effects of the brackish irrigation water.
This experiment revealed an effective strategy for growing peas with brackish tap water.
By investing a few hours over a span of 59 days in this experiment, we learned that neither biostimulant was effective alone under our growing conditions. But when the two biostimulants were used together, we were able to overcome the negative effects of brackish water.
Can we improve on these results?
We know that that Bio 1+2 treatment was superior to any other formula we tried. But this is not the best we can do. Our Brix readings still lagged behind ideal scores by at least 4 points. If we can raise the Brix reading by 4 more points, our plants will be better nourished, and they will exhibit better resistance to cold and other stressors. They will also produce pods with better flavors. In the spring, we plan to repeat the experiment, replacing the Bio1 and Bio 2 treatments with fungal rich compost , either alone, or in combination with Bio 1+2. Adding fungi will help complete the soil food web. This is expected to improve the nutrient cycling and increase plant tolerance to poor quality water.
The Final Take-Home Message
Soil additives like humic acids, trace element mixes, and plant performance enhancing microbes all have a place in making crops more nutritious. However, specific needs will vary with every operation. The most successful operations are open to exploring new approaches. However, it is important to recognize that even products with strong claims on the label may not work in every growing environment. On site testing at small scales can help growers identify those approaches that work best under their own management conditions.