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Unlocking Nutrients in the Soil Food Web

Lately we have gotten the learning bug, and we’ve been teaching ourselves all about the soil food web, and the bacteria, fungi, arthropods, and other creatures that inhabit and enrich our soil.

Our latest experiment with different soils yielded some really interesting results.

About two months ago we planted tomato seedlings in two different types of soil, just to see what would happen. We planted two trays of tomato seedlings. Each tray was planted half with Miracle Grow potting mix and half with our own in-house mix consisting of coconut coir and worm castings. Being in the same tray, they were all watered and treated the same.

The photo below shows a stark difference between tomato seedlings planted in Miracle Grow potting mix (front) and our coco coir mix (back). All the seedlings in this tray are two months old—they were all planted at the same time. The six seedlings planted in Miracle Grow are only about 2-3 inches tall, if we’re generous. They didn’t amount to much. The five behind, planted in our seed mix are about 8 inches tall on average.

Miracle Grow vs. Worm Castings
Miracle Grow vs. Worm Castings

 

Six of the healthy seedlings were subsequently moved to pots, with more of our rich coco coir and worm castings mix. They have been watered with compost tea and dechlorinated water. They look really good, in my opinion. This is what you might reasonably expect to see after being transplanted to a larger pot.

Tomato planted in coco coir and worm castings.

 

Now look at the photo below. This is a plant from that same batch that was subsequently planted in our aquaponic grow bed. I can’t stress enough that this is from the same batch of seedlings, planted on the same day, two months ago. See the empty cells in the tray above? This plant is from those cells. There are several plants in this bed – all of them are over 18 inches tall.

Tomato plant in aquaponic grow beds
Tomato plant in aquaponic grow beds

 

For comparison, here is a fancy chart showing the relative growth of each of these different tomato plants. As you can see, the tomato in the aquaponic grow bed is out of control.

Tomato growth comparison at 8 weeks.
Tomato growth comparison at 8 weeks.

 

One of the key features of aquaponics is that it produces bountiful amounts of nitrogen, which probably accounts for the ridiculous amount of growth in the tomatoes planted in the grow beds. We are learning, however, that in spite of the amazing growth the soil food web in the grow beds is not quite complete. There are other nutrients that don’t seem to be present, or if they are, are not accessible by the plants, such as phosphorus. We have been adding compost tea, along with fungal, archaeal, and bacterial inoculants in the hopes that these microorganisms will flourish and begin to unlock the nutrients that the plants need to thrive.