Biostimulants Boost Plant Growth in Brackish Water

The Best Way To Tell Which Biostimulant to use is to Test it Yourself

Biostimulants are additives that boost plant productivity, but lack the macronutrients necessary to label them as fertilizer.  Often organic, biostimulants are useful for supporting plant production 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. This is one reason expert growers must experiment with new approaches.

In recent years, several gardeners  have asked me for recommendations regarding Bloomin Minerals.  Bloomin Minerals is a high quality humate with a rich blend of trace minerals, and it is available in garden scale volumes from our online store.

Here in the Southwest, soils generally lack humates and living organic matter.  They also tend to be alkaline, which can limit mineral uptake.  Bloomin Minerals, won’t fix this by itself, but  in combination with other management practices, Bloomin Minerals can be a positive addition for some soils.

Many Southwest gardeners bypass the existing soil and opt for containers with commercial garden soil.  Will added humates like Bloomin Minerals, or microbially rich biostimulants help a rich, black, soil?  You could get some clues with professional soil testing, or you can run an experiment and evaluate the outcomes.  Don’t worry, you don’t have to write a thesis.  You don’t have to master statistical analysis.  You don’t even have to present your results.  But a replicated design with reasonable controls can offer powerful insights into practices that improve your production.

In southern New Mexico, many gardeners are faced with poor water quality.  To answer the question of how biostimulants might enhance container gardens irrigated with alkaline tap water, I ran the test below.

Now, get ready.  The rest of this article may sound as enticing as a peer reviewed research papers.  But it is not intended to pass for a full blown scientific study. I simply want to demonstrate steps you can follow at home to test amendments in your garden. Including details makes it easier for you to interpret the results.

The goals of this experiment were:

  • to evaluate  the effects of commercial biostimulants, including Bloomin Minerals , on container grown cool season vegetables irrigated with tap water.
  • to  compare the additive effects of added trace minerals (Bloomin Minerals ) and added plant growth promoting microbes (contained in the other commercial biostimulant).
  • to demonstrate the value of on site experiments to guide management 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:

Figure 1. Color coded 5 gallon buckets allowed for rapid identification of treatments.  After planting, the soil was covered with straw mulch to retain moisture.

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 (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 -Commercial Biostimulant Treatment (Bio 2). 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 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 Commercial Biostimulant (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 Management

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

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.

Results

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
Control 0 9
Bio 1 0 4
Bio 2 5 8
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 2. Leaves selected from mid stage growth 36 days after planting. Chlorosis (yellowing) visible in the control and in the individual biostimulant 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 significantly more vigorous growth than the other treatments.

 

 

Interpreting the Results

Insights gained from this simple experiment are summarized below.

Peas don’t like hard, alkaline water. 

The overall performance 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 Bio 1 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.  Since plants were being grown outdoors, it is thought that a bird or small rodent may have removed the plants.

The low number of emerged seedlings in Bio 1 treatments 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 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.  

The take home message is that neither the lackluster performance of  the control plants and theBio 1 and Bio 2 treatments, nor the remarkable difference observed when the two biostimulants were combined was predicted in advance.  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 many of the negative effects of brackish water at our location.  

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. 

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