Harnessing the Sun for On-farm Fertilizer Production

Harnessing the Sun for On-farm Fertilizer Production

Summary

Agriculture is highly dependent on fertilizer made through energy-intensive industrial nitrogen (N) fixation. As energy prices increase, so does the price of fertilizer. Biological N-fixation using cyanobacteria has the potential to supply N to crops while reducing input costs and increasing energy-efficiency. Our goal is to develop and test an on-farm biological N-fixation system. The primary scientific components include development and optimization of cyanobacteria-based N-fixation, on-farm testing through participatory research and economic analysis. Extension fact sheets, field demonstrations, a webcast, newsletter articles and presentations will raise awareness and educate producers and professionals regarding this new technique.

Objectives/Performance Targets

Our objectives are:

(1) to evaluate cyanobacterial species and growth conditions necessary for biofertilizer production;

(2) to evaluate the economic and social feasibility of on-farm or community-scale fertilizer production using a biological N-fixation system;

(3) to optimize the harvesting, processing and application of cyanobacteria-fixed N through on-farm testing;

(4) to inform the bioreactor design and utilization of biofertilizers through consultations with farmers; and

(5) to develop educational materials providing information on the production and utilization of cyanobacteria-based N fertilizer and disseminate that information to farmers and agricultural professionals through a variety of means.

Accomplishments/Milestones

Objective 1: to evaluate cyanobacterial species and growth conditions necessary for biofertilizer production.

Task 1a. Evaluate the biomass production and N-fixation efficiency of test inocula under optimal growth conditions.

Soil, water and sediment samples have been collected from 24 locations around the Front Range and Western Slope of Colorado, including wetlands, lakes, rivers and farmers’ fields. Nitrogen-fixing cyanobacteria have been cultured using two methods: (1) construction of Winogradsky columns or (2) selective sub-culturing with Allen and Arnon media. Selective sub-culturing has proved to be the fastest means of enriching for nitrogen-fixing cyanobacteria.

Currently cultures are grown under 12 hour light (2500 lux): 12 hour dark cycles, ambient temperature and aerated by means of a low speed (100 rpm) orbital shaker. Filamentous heterocystous cyanobacteria are the dominant type of cyanobacteria selected for under these conditions (Figure 1).

Based on morphology, we have identified cyanobacteria from at least four genera, including Nostoc, Anabaena, Calothrix and Cylindrospermium, in our environmental cultures, with strains from Nostoc and Anabaena being the most commonly represented.

Task 1b. Determine the tolerance and performance of test inocula subjected to environmental stresses and variations in operational parameters from baseline conditions.

Based on preliminary experiments, aeration is key to enhancing nitrogen-fixation in filamentous, heterocystous strains of cyanobacteria. To simulate cultivation of cyanobacteria in an open pond system, four test cultures were inoculated into large aquariums containing Allen and Arnon media. Each culture was grown with or without aeration. A sample from each tank was analyzed for total nitrogen analysis using the Kjeldahl method. The aerated cultures fixed over 2.5 times more total nitrogen (p=0.006) than those that were grown under static conditions (Figure 2).

The composition of the nutrient media is another critical component that is currently being evaluated. Cyanobacteria fix their own carbon and nitrogen from the carbon dioxide and nitrogen in the atmosphere by photosynthesis and nitrogen fixation, respectively. The most critical nutrients for cyanobacteria are the trace metals required by the enzymes involved in these processes.

The micronutrient solution in Allen and Arnon is more complete than that of BG-11 in that it contains vanadium (Figure 3A). However, BG-11 has higher concentrations of some micronutrients. A modified Allen and Arnon media has also been developed, which has a double-strength concentration of micronutrients.

When four environmental cultures were grown side-by-side in Allen and Arnon and BG-11 media, three of the cultures showed greater biomass production with Allen and Arnon media (Figure 3B). One culture, the most productive strain to-date, showed improved growth with the BG-11 media. When compared overall, there was no significant difference in the biomass production between those grown in Allen and Arnon and those grown in BG-11 media (p=0.272).

We intend to carry out additional studies to evaluate the optimum nutrient solution for each culture.

Task 1c. Determine potential methods for efficient harvesting of nitrogen from cyanobacterial cultures.

Some strains of cyanobacteria possess gas vacuoles, allowing them to float. Other strains naturally settle (Figure 4). Thus cells are naturally able to concentrate themselves either at the surface or at the base of a pond or reactor, greatly facilitating harvesting. Both flotation and settling will be evaluated as potential methods of harvesting cyanobacteria. The methods will be compared based on four criteria: (1) efficiency of recovery, (2) settling/flotation time, (3) energy requirements and (4) cost of required harvesting equipment.

Task 1d. Evaluate performance of selected inocula for growth in laboratory scale bioreactors.

We have constructed an experimental apparatus that can be used for evaluating multiple cultures under varying environmental conditions (Figure 5). Using these culture tanks, we have conducted preliminary tests to develop standard methods and to evaluate the performance of different types of media. This set-up will be used for evaluating the performance of inocula for scale-up into a bioreactor or pilot-scale open pond system.

Objective 2: to evaluate the economic and social feasibility of on-farm or community-scale fertilizer production using a biological N-fixation system.

Progress includes a categorization and characterization of the main sectors of potential adopters, qualitative analysis of soil N sources and the economic decision-making framework for each, and direct interviews with representatives from all categories to determine level of potential interest in adoption of a cyanobacterial bio-fertilizer.

Potential adopters we have examined for on-farm adoption of production and use can be categorized as follows: small organic farms, medium organic farms and subsistence farms. Characteristics of each:

Small Organic Farms: 2-15 acres of land upon which varied and integrated crops are grown including vegetables, fruits (both tree fruits and others) and often flowers. These farms represent a growing trend in the U.S. for Community Supported Agriculture (CSA), providing produce to local buyers. All those interviewed classify themselves as “organic” or “natural” and are intensely concerned with sustainable practices; however, most are not USDA-certified organic. They rigorously avoid all synthetic inputs and chemicals. Currently, N is sourced through integrated on-farm soil management and growing methods such as biodynamics, composting and manure management and cover cropping. Few, if any, purchased soil amendments are used.

Large Organic Farms: own and/or manage more than 2,000 acres. These growers have found success by specializing primarily in vegetable crops for regional, national and even export markets, increasing the value proposition with the USDA Organic label. Due to large areas of monocropped land, there is significant need for inputs that would facilitate growth while simultaneously keeping with organic requirements. Growers interviewed exhibit a personal belief that organic farming practices are best; however, business logic and acumen is what has driven their success to this scale. Currently N is sourced through a combination of purchased compost, fish emulsion, manure, guano and cover cropping.

Subsistence Farms: An international MBA team at Colorado State University has been engaged to explore a sustainable enterprise business model that would provide small-holder (two – five acres) growers in developing nations with this bio-fertilizer technology. The team had opportunity to interview subsistence growers in India and Ethiopia. These growers produce small crops on one to three acres for their own consumption, as well as cash crops for sale (often less than US$500 per year). Due to a range of factors—including high real cost, poor infrastructure and highly constrained budgets, little if any commercial inputs are utilized. Composting is utilized to the extent that manure is available and not being used for fuel or construction materials.

Varying levels of interest for on-farm production of N fertilizer exist across all three categories of farmers. Small-scale organic farmers typically were committed to producing their own inputs and were initially not interested in the cyanobacterial fertilizer, both because of economic constraints but also due to their commitment to an existing philosophical approach (such as closed-loop or bio-dynamics). However, interest was piqued when noted they could possibly grow their own. The larger-scale organic growers expressed keen interest in on-farm production stating they had the necessary land, water and production capacity. Subsistence farmers also expressed interest; however, it was tempered with concern for the amount of space needed for such production and wariness about the overall effectiveness of such a product. However, the potential for positive impacts on health and income was perceived to be great. Ultimately, all three categories of growers are interested in on-farm production. However, for both the large organic and subsistence growers, other factors were identified that may drive the preferred method of production away from a fully distributed model (of on-farm production) towards a somewhat more centralized model (such as at nearby cooperatives with larger-scale production facilities to service a given region). These factors include the productivity of the cyanobacterial cultivation technology itself, economies of scale in that technology, capital requirements for building production facilities and risk sharing.

Next steps include a more quantitative analysis of price points and potential market size in the U.S. organic fertilizer sector and determination of market feasibility requirements for cyanobacterial bio-fertilizer to penetrate the conventional agriculture market.

Objective 3: to optimize the harvesting, processing and application of cyanobacteria-fixed N through on-farm testing.

Task 3a. User-informed development of cyanobacterial production and harvesting systems.

We are planning a workshop with our farmer-cooperators in January 2011 in order to share our research results to-date and receive their input on necessary characteristics of an on-farm bio-fertilizer production system. This workshop will be critical to the design of our on-farm pilot.

Task 3b. On-farm testing of fertilizer produced and harvested in the laboratory.

In the winter of 2011-2012, we will use bio-fertilizer produced at Happy Heart Farm (Task 4b) for a greenhouse evaluation of the efficacy of the fertilizer as compared to manure and urea, typically-used organic and conventional fertilizers, respectively. In spring 2012, fertilizer trials will be initiated in the field.

Objective 4: to inform the bioreactor design and utilization of biofertilizers through consultations with farmers.

Task 4a. Design and evaluation of scaled-up photobioreactors and harvesting systems.

Following the farmer workshop in January (Task 3a), we will design the raceways, aeration system and solar dryer to be installed at Happy Heart Farm in the spring of 2011.

Task 4b. On-farm testing of scaled-up photobioreactor and harvesting a system at Happy Heart Farm.

In the spring of 2011 we plan to build two 100-gallon aerated raceways and a solar dryer at Happy Heart Farm for on-farm, mid-size evaluation of the technology. Growth and N-fixation rates will be monitored throughout the summer. Dried cyanobacterial bio-fertilizer will be collected throughout the summer in order to monitor production rates and to collect bio-fertilizer for use in Task 3b.

Objective 5: to develop educational materials providing information on the production and utilization of cyanobacteria-based N fertilizer and disseminate that information to farmers and agricultural professional through a variety of means.

The educational aspects of this project will be based on the on-farm research in the summer of 2011 and will, therefore, not begin until December 2011.

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• Figure 5
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Impacts and Contributions/Outcomes

In the short-term, we will be developing an increased understanding and awareness of production and utilization of cyanobacterial bio-fertilizer as an alternative. In addition, we will develop the skill set necessary to produce and utilize cyanobacterial bio-fertilizer in both the scientific and farming communities. In the medium-term, we will be working with organic and conventional fertilizer certifiers to achieve regulatory clearance for the use of cyanobacterial bio-fertilizer in organic and conventional farming systems. We will also develop improved decision-making abilities by both the developers and users of this technology. In the long-term, we aim for reduced fossil fuel use and greenhouse gas emissions from fertilizer manufacturing and the expansion of rural jobs, a reduced-cost on-farm fertilizer source and alternative income opportunities.

Collaborators: