The Use of Cyanobacteria Biofertilizers to Increase Crop Productivity, Improve Soil Health, and Agricultural Sustainability in Florida

This Research and Education Grant project was awarded a 2022 James Harrison Hill, Sr. Young Scholar Enhancement Grant award in the amount of $4,433. The award provides high school and undergraduate college students the opportunity to conduct sustainable agriculture research, as part of an existing Research and Education Grant project.

View the project report

Commodities

• Vegetables: okra, tomatoes

Practices

• Crop Production: fertilizers, nutrient management, water management
• Energy: byproduct utilization
• Production Systems: organic agriculture
• Soil Management: soil quality/health

Biofertilizers are defined as organic substances containing various microorganisms that improve soil and crop productivity. Cyanobacteria have become an important addition to biofertilizers due to their enhancement of crop production and soil health. However, abundance of cyanobacteria in water can develop hypoxic conditions and cause harmful effects to aquatic organisms. Lake Okeechobee and St. Lucie River of Florida are frequently subjected to cyanobacterial ‘blooms’ that degrade water quality and incur significant environmental, ecological, economic, and societal impacts. Cyanobacterial blooms covered 60% (894 km²) of Lake Okeechobee during June-October 2018. Chemical treatments attempted to manage cyanobacteria population of the Lake have not been successful and created unintended water quality issues. Therefore, we propose to physically remove cyanobacteria from the Lake and utilize the resultant materials as biofertilizer for sustainable tomato and okra production.

Cyanobacteria biofertilizer provide macro and micro-nutrients in the soil and improve nutritional properties (antioxidant, anthocyanin, carotenoids, and chlorophyll contents) of vegetables. Cyanobacteria also increase soil organic carbon (SOC) accumulation, improve soil structure and biodiversity, enhance soil enzymatic activities, and protect plants from pathogens. We estimated that cyanobacteria biofertilizer would reduce 40% fertilizer cost than synthetic fertilizers for vegetable productions. Nutrients in cyanobacteria biofertilizer are in organic form and will be released slowly as the materials decompose. This process is similar to commercially available slow-release fertilizers, that have become standard practice in reducing nutrient leaching and water quality protection. Therefore, this approach is expected to increase return on investment (ROI) of agricultural growers while preserving ecosystem quality. To our knowledge, no field-based experiment in the US have evaluated the effects of cyanobacteria biofertilizer on crop productions and soil health.

This three-year study will evaluate (1) the efficacy of cyanobacteria biofertilizer in improving crop productivity and soil health, (2) the soil and water quality parameters from agricultural fields treated with cyanobacteria, and (3) the economic efficiency of replacing synthetic fertilizer with cyanobacteria biofertilizer.  

We are collaborating with the US Army Corps of Engineers (USACE) and AECOM company to collect cyanobacteria from Lake Okeechobee using micro-flotation techniques. Collected cyanobacterial mats will be processed and packed as biofertilizer at Florida International University. We will test the efficacy of cyanobacteria biofertilizer for vegetable production both at FIU greenhouse and cooperative farmer's field. Yield parameters and compositional analyses of tomato and okra will be determined. Physicochemical and microbiological parameters of soils will be measured to evaluate the effect of biofertilizer in agricultural fields.

Cyanobacteria samples (n = 8) collected from Lake Okeechobee showed 1.79% N (similar to other organic fertilizers), 19.6% total C, high Fe (2005 ppm), other micro-nutrient contents, and lower C:N ratios. A preliminary pot experiment growing okra using cyanobacteria biofertilizer showed (at 7-weeks) similar plant height (69 cm), stem diameter (11.2 mm), and leaf chlorophyll content (51) compared to synthetic fertilizer and higher values than unfertilized control pots.

We expect major outcomes of this project will be restoration of Lake Okeechobee ecosystem, higher crop production and revenue generation, soil health improvement, and educational benefits to growers and students on organic agriculture.

Overall, this project will follow a system-based research approach where optimum crop yield can be obtained without disrupting the harmony of multiple sustainability components (environmental, ecological, economic, and social). This project will address the key question: “Can we increase overall agricultural sustainability by using the waste product of one system as a viable resource for another?” Specific objectives of this project are:

1) To evaluate the chemical and nutritional properties of cyanobacteria collected from Lake Okeechobee and the St. Lucie River ecological areas of Florida

We propose to quantify pH, organic matter content, essential macro (N, P, and K), secondary nutrient (Ca, Mg, and S), and micro (Fe, Zn, Mn, B, Cu, Mo, Cl, and Ni) plant nutrients available in cyanobacteria samples. Cyanobacterial mats will be collected from various locations of the Lake and surrounding area for chemical analyses. We hypothesize that analyses of nutritional and physicochemical properties of cyanobacteria will assist in developing efficient fertilizer application planning in the greenhouse and field trials.

To ensure the safe use of cyanobacteria biofertilizer in the field, microcystin (a common cyanotoxin) concentrations of collected cyanobacterial mats will be analyzed in the laboratory at different stages of biofertilizer development. This experiment will be based on previous study conducted by Co-PI, Dr. Jayachandran and colleagues (Ramani et al., 2012) who found that more than 75% of the cyanotoxins were degraded within 3-weeks after cyanobacteria harvesting from Lake Okeechobee. Our team estimated that it will take about 45 to 50 days to process the fresh cyanobacteria mats into a dried biofertilizer powder (collection, transportation, drying, grounding, and packing). Therefore, the rate of cyanotoxin degradation over time will be calculated from day of collection (time zero; T0) to 50 days after collection (prior to crop application; T50). We will measure the cyanotoxins in cyanobacteria samples every 10 days to develop the ‘decay rate curve’ of the toxin in biofertilizer. We hypothesize that microcystin concentrations in the cyanobacteria biofertilizer will be degraded to less than 1 ppb (WHO standard guideline) and safe for field application.  

Additionally, we will test the shelf-life of the cyanobacteria biofertilizer. Some cyanobacteria biofertilizer samples produced in first year (2021-2022) will be kept in a cool, dry place and the nutritional properties of those samples will be analyzed in project years 2 and 3 to determine the shelf-life of the fertilizer.

2) To assess the efficacy of biofertilizer application for crop production and improving soil health

In first section of this objective, we will quantify yield and physiological parameters of tomato and okra at different plant growth stages both in a controlled environment (FIU greenhouse) and in field trials (collaborative farmer’s field). We hypothesize that the application of cyanobacteria biofertilizer will improve soil fertility and increase crop production. The second section of this objective will test the effect of cyanobacteria biofertilizer in improving soil health which is specifically important in South Florida where organic matter content is less than 1%. We hypothesize that extracellular polysaccharides released by cyanobacteria in the soil will improve overall soil health components (soil aggregate stability, soil bulk density, and water holding capacity). Measuring different fractions of soil carbon (total C, organic C, particulate C) will provide us the idea of different ecosystem services cyanobacteria biofertilizer can offer.

3) To develop the ‘mineralization rate curve’ of nutrients released from cyanobacteria biofertilizer

Nutrients in cyanobacteria biofertilizer are in organic form and will be released slowly as the organic materials decompose. This process is similar to commercially available slow-release fertilizers, the use of which have become standard practice in reducing nutrient leaching and water quality protection. Therefore, we will develop the ‘mineralization rate curve’ of nutrients in the soil after cyanobacteria biofertilizer application. We hypothesize that developing ‘mineralization rate curves’ of nutrients will help us evaluate the amount of nutrients solubilized each year from this biofertilizer application. Additionally, we will get a better idea about long-term residual effect of nutrients (how much remained in the field) and annual soil organic C accumulation from cyanobacteria application in agroclimatic conditions of South Florida.

 4) To monitor nutrient loss (soil and water quality) from the soils

This objective is to quantify the loss of nutrients (inorganic N and soluble reactive P) from cyanobacteria biofertilizer applied plots. As suggested by one of the reviewers that installing lysimeters in the field to conduct leaching experiments is beyond the scope of this study; therefore, the leaching experiments will be conducted in the FIU laboratory as column studies. Column study in leaching experiments for biofertilizer treatments were reported in previous studies (Zhao et al., 2009; Rashmi et al., 2020). Details of the column experiment is discussed in ‘approach and methods’ section. We hypothesize that improved soil structure and slow nutrient release in biofertilizer applied field plots will have lower amount of nutrient loss compared to the plots receiving synthetic fertilizers. 

5) To assess the economic benefits of biofertilizer application for vegetable productions in Florida        

We will run stochastic economic models to integrate inputs (seeds, fertilizer, labor etc.) and outputs (crop yield, price, market demand etc.) for assessing the economic benefits of cyanobacteria biofertilizer in tomato and okra productions. We realize that there are uncertainties with crop yields, costs, and market prices under both conventional and proposed organic farming approaches. The stochastic economic model will utilize a Monte Carlo approach to account for the above uncertainties and help assess incremental (additional) net profits and variability in returns. We hypothesize that organic farming will generate higher profits as well as lower economic variability (risks) for growers than conventional farming practices.