Does reduction of nitrate inputs in pasture land treated with Chlorella vulgaris result in cost savings and healthier soil and grass?

Progress report for FS22-341

Project Type: Farmer/Rancher
Funds awarded in 2022: $10,975.00
Projected End Date: 03/31/2024
Grant Recipient: Sweetgrass Garden Co-op
Region: Southern
State: South Carolina
Principal Investigator:
Dale Snyder
Sweetgrass Garden Co-op
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Project Information


In response to the negative impacts of NPK on soil and climate, there has been an increased interest in organic 

growing methods.  One of these is the use of biostimulants, which the 2018 US Farm Bill described as compounds 

or organisms that stimulate natural processes to enhance growth, yield and fertility.  

During the last three years we have studied the effects of the micro-application of a live, green algae, Chlorella vulgaris.  

In a SSARE funded study last year, we tested its effects on tomatoes and found that yield was higher in rich soil (treated

 with compost), and in poor soil (not composted).  In previous turf trials we observed improvement in measures of 

soil fertility including organic matter, soil respiration, and soil organic nitrogen (Haney testing).   

A recent study conducted by an affiliated farmer in Nebraska found increased hay production (sorghum hay) with the 

addition of algae to his usual NPK input.  Of particular interest was a 75% increase in protein content, and a 30% rise in 

lipids.   Of concern was a marked increase in nitrate content with algae treatment.  After consultation with his nutritionist,

 we conclude that adding algae to a large dose of synthetic nitrogen is too much.  


In this study, we will analyze nitrates in pasture grass to determine nitrate content with reduced nitrogen input, and no input. 

This study is designed to determine whether algae treatment would be enhanced with the addition of a small quantity 

of NPK (25% of the usual input), or the addition of a carbon source such as biochar.  

The following study conducted on horse pasture addresses those issues.


Project Objectives:


The study will be conducted at the Iron Horse Farm (IHF) on Johns Island, SC.   For 18 months, algae has been the 

only nutritional input, and the horse farm owner, Allen Reed has been satisfied that quality of the pasture, and 

particularly the color of his grass has improved (multiple studies have shown increased chlorophyll with algae treatment).    

The study will be conducted in four contiguous sections of pasture measuring 1-2.5 acres.  


Sections will be treated as follows: 

Pasture 1A: (nearest Bohicket Rd):  Algae (Chlorella vulgaris)+ 25% NPK 

Pasture 2A: Algae alone   

Pasture 3A-north half:   Algae alone  

Pasture 3A-south half:  Algae + Biochar

Pasture 3B-north half:  Algae alone 

Pasture 3B-south half:  Biochar Alone 

Pasture 3C: Control (no commercial fertilizer or Algae)

Pasture 4: Control (100% recommended commercial fertilizer)  



A single application of NPK, based on 25% of the recommendations based on soil tests, will be administered 

with the emergence of perennial grass (Bahiagrass) in the early spring, usually the second week in March and

again as needed based on sufficient forage required by grazing horses.

A single application of biochar will be applied at the same time, as will the first application of algae.  A second 

application of algae will be added 2 weeks later, then at 4-week intervals through the growing season. 



1. Growth:  The first assessment will be when the Bahiagrass is well established. 

After a first mowing, it will be unmowed until the first test-section reaches 5 inches in 

height.  At that time the height of grass in all of the test sections will be measured.  

Grass mowed from a 20 x 20 foot representative plot in each test 

pasture will be weighed. 


2.Chlorophyll:  levels of chlorophyll a and b will be assessed (Regen Ag Lab, Pleasonton, NE) to make our study consistent with current scientific literature and to roughly parallel photosynthetic activity. 


3.Nutritional content:  standard analysis will include crude protein, nitrates, fat and minerals. 


4.Haney soil testing (baseline and 2 weeks after the third algae application, or 6 weeks 

after emergence). 

5. Economic analysis of the different treatments as compared to a control of commercial fertilizer and no fertilizer. 


Materials and methods:

2022 Annual Report

Does reduction of nitrate inputs in pasture land treated with Chlorella vulgaris result in cost savings and healthier soil and grass?


Live algae as a biostimulant may have been used as far back as 2000 years.  University research began in the 1970’s and documented its efficacy for plant growth and yield of rice, maize, wheat, and multiple other vegetable crops.  Fewer studies have been published describing its effect on pasture.

The present study tested the effect of live Chlorella vulgaris on heavily grazed horse pasture on Johns Island, SC.  This 10-acre farm has 7 fenced pastures, each of them used as a study pasture.  The perennial grass was Bahia, and winter rye grass was planted in October.  The study was initiated in April 2022 and the last observations were made in April 2023.

Study groups included 1) treatment with algae alone, 2) treatment with algae + 25% of the recommended NPK input, 3) treatment with 100% of the recommended NPK, and 4) a control pasture with no input.   There were no replicates, the standard agronomic method to assess effect.


The assigned treatment for each of the study pastures was randomly chosen by the property owner who drew lots (without knowledge of the treatment assignment).  The pastures varied in the quality of grass;  5 of the 7 were considered good quality and were used in the randomization.  One other had never grown well for a variety of reasons, and one was a severely over-grazed paddock.   

Live chlorella vulgaris was purchased from Enlightened Soil Corp on Johns Island, SC (the product is called EnSoil Algae).   An algae concentrate in its aqueous growth medium contained a minimum of 10 million chlorella cells per mL.  One liter of this was diluted to cover 4.5 acres using standard spraying equipment.  At this dilution, the algae dose was 50,000 cells per square foot of pasture.   Algae were applied five times during the study year: the first two at 2-week intervals, then at approximately 3-month intervals.  Liquid chemical fertilizer NPK was applied twice: April 14, 2022, and again on June 6, 2022.

The primary endpoint was grass quality.  This was a qualitative assessment and the study used two independent observers who were not aware of treatment assignment.  One was the property owner who made daily observations.  Another was our Ag Extension Agent who made a single visit in late June, 2022.  They ranked each of the five pastures that were randomized, and ranked them as best, second best, 3rd , 4th , and 5th best.  They made their assessments based on grass height, thickness, and color.

A secondary endpoint was soil test results.  Haney testing and phospholipid fatty acid (PLFA) analysis were done on 4 occasions.  Each pasture had landmarks that allowed sampling from the same general area, and 4 samples from the area were blended for testing.  Samples were collected with a soil augur to a depth of 4 inches.


Research results and discussion:

Primary end-point, grass quality: 

The five ranked pastures were contiguous and appeared similar at the beginning of the study year.

(1) The number-1 ranked pasture was treated with algae alone (100% algae). 

(2)  The number-2 ranked was the pasture adjacent to number 1, and was treated with algae + 25% of the usual NPK input. 

(3) The number-3 ranked was the control pasture (no input), and it was contiguous with numbers 1 & 2.  It had more shading than the others and it was more lightly grazed.

(4) The number-4 ranked pasture, treated with 100% algae, was not grazed

(5) The 5th ranked pasture was treated with NPK alone.

(6) The next ranked pasture was treated with 100% algae. This was considered problem ground where grass had never grown well due to the death of several grand trees due to hurricane and lightening damage.

(7) The number-7 ranked pasture (100% algae)started as a grassy paddock but was over grazed into a dry paddock.

Soil testing:  The 7 test pastures had both Haney and PLFA testing 4 times during the one-year study.  Of note, all of the pastures had been treated with algae the year before the study, and none had received NPK.

The soil test results are being analyzed by an agronomy consultant, and will be added to this report.


There has been extensive, university-based study of chlorella vulgaris as a biostimulant.  The present results provide real-world experience on pasture grown on the sandy soil of Johns Island, SC.  They are consistent with published experience: algae appeared effective in promoting growth of the Bahia grass horse pasture.  Addition of 25% of the usual NPK input to algae treatment did not boost growth or grass quality.

The apparent result was convincing enough that the farm owner has elected to forgo use of synthetic NPK fertilizer going forward, and will use live chlorella vulgaris in its place.



Participation Summary

Educational & Outreach Activities

Participation Summary:

Education/outreach description:

No outreach activities at this time.

Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.