On-farm Cyanobacterial Bio-fertilizer Production to Reduce the Carbon Footprint of Organic Fruit and Vegetable Production

On-farm Cyanobacterial Bio-fertilizer Production to Reduce the Carbon Footprint of Organic Fruit and Vegetable Production

Objective 1) Optimize the yield and efficiency of an on-farm cyano-fertilizer production system 

 Task 1.1 – Determine if CO2 bubbling will enhance growth and N-fixation of cyanobacteria grown in outdoor raceways. 

Summer 2016 field experiments utilized CO2 to maintain a sufficiently low pH to improve dissolved inorganic carbon (DIC) availability in raceway cultures throughout the day, especially when photosynthesis rates are high between 10 a.m. and 2 p.m.

During the summer 2016 field season, we conducted experiments to better manage light availability of Anabaena sp. cultures. We compared two inoculation densities, both higher than historical inoculation rates, in an effort to decrease photo-inhibition and photo-damage. We hypothesized that this would improve outdoor culture survival rates and increase daily productivity (biomass gains) and final 14-day batch biomass and N concentrations. In addition, we performed a phytohormone assay to determine if certain phytohormones and phytohormone concentrations are consistently produced during a 14-day batch period. Cyanobacterial-based phytohormone extracts have been shown to improve growth, yields and drought tolerance in a variety of crops.

Increased inoculation rates, decreased culture depth, and CO2 supplementation achieved 14d batch biomass and N concentrations of 542 mg L-1 and 60 mg L-1, respectively. This is a 225% increase in 14-day batch biomass and N concentrations.

Six phytohormone related compounds were detected during the phytohormone assay – abscisic acid (ABA), salicylic acid (SA), one cytokinin (CK), trans zeatin riboside, and three auxin compounds: indole 3-acetic acid (IAA), indole 3-acetamide, an IAA precursor, and Indole 3-carboxylic acid. Concentrations of auxins, CK, and ABA were consistent across experiments, while SA showed more variability.

A cyanotoxin assay conducted using gas chromatography-mass spectrometry did not find detectable concentrations of microcystins, anatoxin-a, or cylindrospermopsin.

 Task 1.2 – Evaluate batch vs. semi-continuous growth of cyanobacteria. 

This task was completed in 2015.

 Task 1.3 – Explore methods to optimize light absorption. 

We compared batch culture concentrations under full outdoor light exposure to that under high tunnels. High tunnels may provide protection when photosynthetically active radiation is highest and cultures are dilute, but may also limit light availability later in the 14-day batch period when cultures become increasingly dense.  No significant differences were seen in 14-day biomass or N concentrations between high tunnel and outdoor troughs. There was also no significant difference in 14-day biomass and N concentrations between the two inoculation rates.

However, results from the 2016 field experiments showed that we can increase 14-day batch biomass and N concentrations by increasing inoculation densities and decreasing culture depth. Increasing inoculation densities can protect cyanobacteria from photo-damage, and decreasing culture depth reduces self-shading and increases light availability.

No net gains in biomass were recorded on cloudy days during the second week of production, suggesting that light can be limited in on-farm production. Production parameters designed to allow for increased light availability (e.g. shorter batch periods, shallow raceways, increased mixing, etc.) could increase growing season yields.   In fact, when inoculation rates were increased in conjunction with decreased culture depth and CO2 supplementation, the 14-day batch biomass and N concentrations increased by 225%.

Objective 2) Evaluate the utilization of cyano-fertilizer in irrigated fruit (peaches) and vegetable (lettuce, sweet corn) systems 

 Task 2.1—Compare cyano-fertilizer with commonly-used organic fertilizers (compost, fish emulsion, feather meal, and blood meal) in terms of impact on plant growth, yield, quality, and N recovery. 

This task was completed in 2015.

 Task 2.2—Assess the effectiveness of cyano-fertilizer in contrast to farmers’ current practice on two working peach orchards. 

This task was completed in 2015.

 Task 2.3–Evaluate the barriers to integration of cyano-fertilizer into current organic farming systems. 

This will be a focus of the project in 2017.

 Objective 3) Quantify the direct costs and benefits of on-farm production and utilization of cyano-fertilizer to optimize economic returns for farmers 

 Task 3.1—Quantify the costs of cyano-fertilizer production as compared to commonly-used organic fertilizers. 

This task was completed in 2015.

Task 3.2—Appraise the economic benefits of cyano-fertilizer use.  

Alternative fertilizer costs are important to the profitability of on-farm cyano-fertilizer production. The higher the costs of the alternative fertilizers, the easier it is to achieve profitability of the cyano-fertilizer. Variability in the price of different organic fertilizers is high; organic fertilizers vary almost 5-fold from the cheapest to the most expensive. Therefore, although profitability can already be shown in comparison to the most expensive organic fertilizers (e.g., alfalfa meal), we are focusing on reducing construction costs and increasing cyanobacterial growth and N fixation in order to be able to compete with the cheaper organic fertilizers. The shipping costs range from 33.3-60.0% of the total costs of organic fertilizers, respectively. In general, the larger the amount purchased, the lower the shipping cost per pound of N.

In addition to direct price comparisons per lb of N, on-site fertilizer production also provides intangible value and addresses farmer needs and preferences. In our market survey, farmers professed needs to reduce the bulkiness and handling costs of low nutrient materials, minimize odor, and allay sustainability concerns. Although, at this time, we cannot assign a hard dollar value to these advantages of cyano-fertilizer, they do play a role in farmer decision-making.

The current cost-benefit ratios for organic fertilizers range from 0.6 – 2.7. Therefore, the current production system already presents a cost savings when compared to alfalfa meal fertilizer. However, to be competitive with a wide range of organic fertilizer products, increasing productivity by 2-3 times, or reducing costs by ½ to 1/3, or a combination of the two will be required.

Based on our on-farm experience applying cyano-fertilizer directly through drip and micro-sprinkler irrigation lines without any clogging, it is clear that applying the bio-fertilizer through fertigation is the most profitable scenario on farms with irrigation systems (nearly all vegetable farms in the western USA are dependent on irrigation).

Task 3.3 –Evaluate the economic feasibility of on-farm production and use of cyano-fertilizer.  

The economic evaluation of the on-farm cyano-fertilizer production system found that cyano-fertilizer is already competitive with the most expensive organic N fertilizers.  However, to be competitive with fish emulsions and blood and feather meals, the cost per lb of N must be reduced to about half of current costs.  Based on the experiments with supplemental CO2 described above, we have more than doubled N fixation rates while increasing costs by only about 20%.  However, we had to reduce the depth of the ponds to 55% of the original depth to achieve these higher N fixation rates, and this change in depth effectively increases the land requirement by 1.8 times.  This is a major detriment to economic feasibility of the current system.

Objective 4) Determine the carbon footprint of cyano-fertilizer compared to other methods of fertilization

Task 4.1—Monitor the N2O and CO2 emissions from cyano-fertilizer applied to land as compared to commonly-used organic fertilizers (fish emulsion, feather meal, and blood meal). 

This task was completed in 2015.

Task 4.2—Modify the Daycent model to include cyano-fertilizer and other organic fertilizers for use in quantifying and comparing the carbon footprint of those fertilizers.

Carbon footprint is commonly defined as the total amount of greenhouse gases produced to directly and indirectly support human activities, usually expressed in equivalent tons of carbon dioxide (CO2). Nitrous oxide (N2O) is a greenhouse gas with a global warming potential of 265–298 times that of CO2. Organic fertilizer application can affect N2O and CO2 emissions from soil by influencing nitrification, denitrification and microbial decomposition.  DAYCENT, a widely used biogeochemical model, has been extensively tested for major commodity crops but not for specialty crops. The objectives of this study were to compare simulated and measured N2O and CO2 emissions from irrigated lettuce plots from different organic fertilizer treatments. The N2O and CO2 emissions were measured during 2014 from a lettuce field (Lactuca sativa L.) with nine treatments: four organic fertilizers (feather meal: FM, blood meal: BM, fish emulsion: FE and cyano-fertilizer: CF) applied at different nitrogen (N) rates (28 and 56 kg N ha-1) and an unfertilized control. The measured data from the low N rate treatments were used for calibration, and the data from the high N rate treatments were used for validation. Comparison of daily N2O and CO2 emissions simulated by DAYCENT and measured from the field yielded coefficients of determination (r2) of 0.0004 to 0.48 and 0.002 to 0.65, respectively. DAYCENT simulated the effect of BM and FM (single application) on both N2O and CO2 emissions better than for FE and CF (multiple applications). Cumulative emissions from DAYCENT were overestimated except for cumulative N2O emissions from FM and BM treatments. The effect of single organic fertilizer applications on N2O and CO2 emissions were simulated well by DAYCENT, and daily N and C mineralization rates could further improve the performance of the single application simulations.

Objective 5) Impact farmer decision-making by sharing results through multiple methods 

 Task 5.1—Develop educational tools including a manual, factsheet, video, C footprint decision tool, and website. 

This will be a focus of the project in 2017.

 Task 5.2—Disseminate educational tools and research results locally, regionally, nationally, and globally. 

Dissemination efforts to farmers, crop consultants, and scientists are described in the Impacts and Contributions/Outcomes section.

 Task 5.3—Quantify and maximize producer adoption through continuous communication and feedback.

Due to the challenges related to land requirement (and subsequent opportunity cost from the loss of that land from crop production), we do not expect producer adoption to take off until we can achieve higher cyano-fertilizer production rates at lower costs.

Collaborators: