Business at Amorgos

[Guillermo Block]

1. Producing fish food
Need to select the fastest growing plants, which preferably also fixes nitrogen from the air. This needs to be a separate system with still water and low oxygenation as oxygen deactivates the enzymes responsible for nitrogen fixation like nitrogenase reductase and thus it hampers the process of nitrogen fixation. Some of the nitrogen fixers act in anaerobic condition to curtail the level of oxygen or allow the oxygen to combine with leghemoglobin.

From “The Feeding Preferences of Grass Carp (Ctenopharyngodon idella Val.) For Ten Aquatic Plants” we get the following table:


A. Azolla
“A Review on Significance of Azolla Meal as a Protein Plant Source in Finfish Culture” describes that Azolla may be used up to 25% of the fish diet. The duckweed fern Azolla is one of the fastest growing and most productive plants on earth and thus can provide a large biomass production (https://www.wur.nl/en/project/Azolla-bio...uction.htm).

Also Azolla is nitrogen fixing: https://www.nature.com/articles/s41598-018-22760-5
"We determined growth, and N and P sequestration rates of Azolla filiculoides in N-free water at different P concentrations" E.g. growth of azolla as function of phospor, in N-free water (so the only N coming is from the air)

https://www.frontiersin.org/articles/10....00442/full
Experimental production reported here demonstrated N-fertilizer independent production of nitrogen-rich biomass with an annual yield potential per ha of 1200 kg−1 N fixed and 35 t dry biomass.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6099237/
“Growing Azolla to produce sustainable protein feed: the effect of differing species and CO2 concentrations on biomass productivity and chemical composition” confirms these numbers:
In a small production system, cultures of Azolla pinnata and Azolla filiculoides were continuously harvested for over 100 days, yielding an average productivity of 90.0–97.2 kg dry weight (DW) ha−1 d−1. Under ambient CO2 levels, N2 fixation by the fern's cyanobacterial symbionts accounted for all nitrogen in the biomass.

Proteins made up 176–208 g kg−1 DW (4.9 × total nitrogen),
Meaning yield / ha / year: 95 * 365 / 1000 = 34.675 tons DW
N2 fixation: 34.675 * 0.185 * 1 / 4.9 = 1.3 tons

For the system we are thus left with a minimal amount of artificial fertilizer, namely Phosphate:



Assuming perfect conversion (some is lost through the fish, some is added by photosynthesis at the plants), we assume 35tons of produce dry weight per ha. Most plants have a high content of water content though. Assuming 95% water content, we can produce up to 700 tons per 35 ton dryweight (=35/(1 – 0.95)) per ha. Which is more than plenty.

B. Duckweed
Spirodela oligorrhiza grown in sterile culture was able to use urea as sole source of nitrogen but only when the pH of the culture medium was below 4.3. Plants inoculated into urea media at pH 6.4 initially made little growth and became nitrogen-deficient in appearance and composition although they contained about 100 μgrams of urea per gram fresh weight of tissue. After a period the pH of the medium usually fell below 4.3 and growth commenced. Growth with other compounds, e.g. ammonium, nitrate or allantoin, as sources of nitrogen was not similarly affected by the pH of the culture medium. Urease activity could always be detected in the tissues of Spirodela oligorrhiza growing on urea. Plants with little or no urease activity soon developed significant activity when inoculated into urea media at pH 4.0. When the pH of the medium was higher there was no increase in urease activity and no growth ensued. Plants growing on urea possessed an activity of about 50 milliunits per gram fresh weight of tissue, but if the pH of the medium fell to 3.5 or lower, the activity present rose to 10 times this level. Urease activity also appeared, in the absence of supplied urea, as plants became increasingly nitrogen-deficient.

Duckweed doesn’t seem to grow much faster than Azolla (Duckweed - a potential high-protein feed resource for domestic animals and fish):

- When effectively managed in this way duckweeds yield 10-30 ton DM/ha/year containing up to 43% crude protein, 5% lipids and a highly digestible dry matter.

- Duckweeds can double their mass in between 16 hours to 2 days under optimal nutrient availability, sunlight, and water temperature. This is faster than almost any other higher plant. Under experimental conditions their production rate can approach an extrapolated 183 metric tonnes/ha/year of dry matter although yields are closer to 10-20 tons of DM/ha/year under real-world conditions (Table 1).

So the only benefit is that duckweed has a higher protein content (43%) than Azolla (30%), at the cost of using Urea fertilizer. No substantial difference in growth-speed is expected.

C. Chara
No numbers are known on nitrogen content of Chara. However it’s well liked by the Grasscarp as most of it was eaten as shown by previously quoted “The Feeding Preferences of Grass Carp (Ctenopharyngodon idella Val.) For Ten Aquatic Plants”.

Edit: There is actually one: http://www.fao.org/3/x6862e/X6862E04.htm
It show's its protein content is alot lower than Duckweed or Azolla (8% +-).

Comparing to Azolla:
“Experimental production reported here demonstrated N-fertilizer independent production of nitrogen-rich biomass [of Azolla] with an annual yield potential per ha of 1200 kg−1 N fixed and 35 t dry biomass.”

We have for Chara:
http://www.herbiguide.com.au/Description...newort.htm
Growth rates around 10 g dw/m2/day (100 kg/ha/day) are recorded in spring, meaning a similar 36 t dry biomass.

And:
“Epiphytic Cyanobacteria on Chara vulgaris Are the Main Contributors to N2 Fixation in Rice Fields”

D. Combine Chara & Azolla ?
Both nitrate fixing. Will try. Probably our best bet. Also, perhaps the Chara can live below the Azolla as it does not grow on the surface of water.

E. Combine Azolla with other plants (e.g. duckweed)
Not completely as good as needs as high nitrate fixing as possible. Other plant will use Azolla’s N2 but won’t contribute.


Based upon all previous written, I will propose some of the workers here to setup a Chara & Azolla test-run. We'll see in some time how that will turn out..