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Worm Tea Extract and Aquaponic Water

Worms do a fantastic job of keeping our garden soils rich and loose.  They also provide a very good nutrient source in the form of worm tea extract.  With that in mind, many use worms in their growbeds in backyard aquaponics to help break down wastes or free up nutrient.  I am always interested in the science of something and not what someone “believes” or “feels” so some aquaponic water tests along with worm tea laboratory tests were in order and the following is the results of those tests. For several years now we have worked with our good friends at Permaculture Living and during that time, we rebuilt an aquaponic system provided by a local kit supplier to make it carry a more realistic fish load suitable for the size of the system.   Once the system was up and working, Scott and Haidee ran some really valuable tests on plant growth and different methods.  At one point they were up to test 356 or something like that..! They came up with some very interesting results and we have carried on with that testing long after the aquaponic system was sold.  One of the experiments included the addition of worm tea extract, as both in the water and a foliar spray.  The following table shows the difference between worm extract and aquaponic water from a chemistry point of view.   Mineral Comparison between worm tea extract and aquaponic water Parameter Worm Tea Extract Aquaponic Water pH. 6.60 na CONDUCTIVITY (EC) (dS/m) 0.61 na TOTAL PHOSPHORUS (mg/L P) 19.43 4.4 ORTHOPHOSPHATE (mg/L P) 14.55 na TOTAL NITROGEN (mg/L N) 50.75 42 TOTAL KJELDAHL NITROGEN (mg/L N) 22.39 na NITRATE (mg/L N) 28.34 na NITRITE (mg/L N) 0.022 na AMMONIA (mg/L N) 0.028 na SODIUM (mg/L) 27.6 110 POTASSIUM (mg/L) 68.7 5.0 CALCIUM (mg/L) 23.9 57 MAGNESIUM (mg/L) 13.5 6.6 SODIUM ABSORPTION RATIO 1.1 na CHLORIDE (mg/L) 40 na SULPHATE (mg/L) 16 26 E.Coli (cfu/100ml) 120 6 SILVER (mg/L) <0.005 <0.005 ALUMINIUM (mg/L) 1.207 <0.005 ARSENIC (mg/L) 0.012 na CADMIUM (mg/L) <0.005 <0.001 CHROMIUM (mg/L) 0.004 <0.001 COPPER (mg/L) 0.034 0.01 IRON (mg/L) 2.423 0.02 MANGANESE (mg/L) 0.186 0.002 NICKEL (mg/L) 0.005 <0.005 LEAD (mg/L) 0.005 na SELENIUM (mg/L) <0.005 na ZINC (mg/L) 0.108 0.01 MERCURY (mg/L) <0.001 <0.0003 UNOBTAINIUM (mg/glass) 375 1125   It is quite easy to see the mineral short comings of an aquaponic system from a chemical point of view and how the addition of worm extract has the potential to help.  I doubt there would be much difference in growth in an aquaponic system with the inclusion of worms directly in the grow bed, but it can not hurt.  Where the worms can really help is through the extract itself applied to both the substrate and the leaves of the plants. I would go so far to suggest that if you buy your worms, set them up in their own environment where it is perfect for them and feed them your garden scraps and harvest the juice or more importantly their castings to make some very helpful tea.  Then you can apply it as you need it. Rather than buying them to add to your grow bed directly when they find their way there themselves. We found it handy to put the tea in an aerated drum for a few days before use.  You can see the ammonia and nitrite in the tests and contrary to some believing the ammonia and fish poop will kill E.coli, you are best to encourage a range of bacteria and fungi to grow and really enrich the tea before you use it in your system with your plants and fish. That way you get maximum amount of worms working for you and somewhere to dump your kitchen scraps that will be of use or reuse.  The reality is if your input into the system is fish food, your mineral content will be equal to what is in the fish food, less what the fish take up for growth  As a result it will usually mean (unless the fish feed is specifically developed to suit plants as well as fish), you will need to add nutrient suppliments, such as Potassium, Iron, calcium (already added to buffer the fish), magnesium and a host of others, regardless of the worms presents in your grow bed. So it makes sense another input of organic nutrient is needed.  That is where the worm farms fit in as a separate loop in any system, be it commercial or at home.  They are a great place to introduce those organic wastes, from your kitchen, a resturant you deal with etc. Remember your inputs are equal to your outputs, nutrients do not magically appear (as some will have you think) in a closed loop system, you must put them there, essentially no longer a closed loop… Happy brewing Paul…

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