I am getting my system up and running. The fish tank and non-grow-bed portion has been functioning for a while now.
I hope to get the growbed section plumbed this weekend weather permitting. This is all in my personal blog, but this discussion has another purpose.
Most of the discussions on new systems I see are based on cycling concerns. Few address how to build the minor and trace elements essential to good plant production.
Of the main elements (NPK), nitrogen is the easiest and seems to be the main concern. I figure potassium is so connected that it will show up at the same time, unless pure ammonia is used.
My real question I suppose is how best to add non-nitrogen elements into the system? Urine will, but it will take a long time. How do you do it?
Urine takes care of most of the same things that fish feed seems to work with. When I did my first pee ponics system I found I needed to dose with Iron and potassium about the same as I did for the regular aquaponics (my well water took care of the calcium adequately.) A bit of seaweed extract is a convenient way to take care of potassium as well as many trace elements.
pH is going to play a really big role in that sort of thing (obviously). There are many, many ways to add or build up a store of micro or trace elements in a given system. And if were talking about solubility, humonia should take less time to become plant bio-available, since those plant essential elements are not bound up in complex organic solids.
With seaweed extract (if we're talking about things like MaxiCrop) what you are paying for there is a cold cell burst extraction process of plant growth hormones (auxins and cytokinins). Which is why Kelp, some of the fastest growing plants on the planet are used. These hormones are extracted from the kelp and bottled.
The NPK and trace mineral content (and the rather high IMO, heavy metal content in the case of MaxiCrop) is pretty much incidental in these products. If all you are after is micro and/or TE's and don't need the growth hormones, then you and your pocketbook are much better off using plain old sea water, or pure un-adulterated dehydrated sea water (salt...some of which is sold with the Mg already extracted, so write the company since they probably don't label it that way...or better yet, do it your self).
There is about as much if not more K in urine than in those products anyways, and certainly more P. the other TE's I'd have to look up, but if memory serves me, they're about in the same range. All of this assumes that you are healthy and that you eat well.
If you have no fish to kill yet, then I imagine you can easily add an excess of such things (micro and TE's) by way of humonia or humonia based extractions by keeping NH4 levels (adding humonia continually) just beneath the threshold at which NH4/3 becomes toxic to bacteria. That should somewhat 'jump start' your system with TE's.
There are other ways to skin that cat as well though...
Oh yeah, almost forgot...worm castings also have a decent amount of trace elements (TE's) along with NPK value. I had an opportunity to teach a class with Jon Parr this past week, and one of the things we put together was a worm tea bubbler. Using a 55Gal blue barrel a couple 5Gal buckets some crafty PVC parts and pieces and just a couple Watts of electricity. It's a really cool way to make a LOT of worm tea at once. Previously I had just stuck a bunch of casting in a nylon sock above an air stone, but I'm going to be building one of these big bubblers and incorporating it into the GH system.
NPK value of castings will vary...So will the amount of TE's. Mine clock in at 2.28%Ca and 1.85%Mg 1.73%K 1.43% N almost 2%P ...and I forget exactly how much of the other TE's.
Right now I am sitting on about 40 gallons of double sifted worm castings..By double sifted I mean they went through a final sifting of 1/8 inch then sat in a tote for a couple weeks then sifted again to remove any worms that might have hatched and any clumps that might have got through earlier
I am using castings if I need 'soil" for my growbeds. Ohter than that, I am going bare-root.
I keep all my vermi-castings moist. I don;t think the bacterial properties are compromised.
Jon Parr said:
Hey Pat, keep in mind those castings don't keep their bacterial properties forever. Mineral-wise, they probably keep forever, but casting tea is more about the microbes than the minerals, to me anyways.