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Comment by bjelkeman-again | Hacker News Reader

See comment here about the pesticides. The article is badly worded. https://news.ycombinator.com/item?id=12658321

Nutrients are added to the irrigation water.

But where do the nutrients come from? The things supplied by fertilizer are not free, which presumably is why the article made such a big deal out of not using fertilizer or soil.

Once the farm's in operation for a while, I'd assume they could compost a lot of the waste material picked up during harvesting. I'm not sure about tomatoes; are the plants destroyed during harvest and grown from seed each season? Some crops are certainly handled that way.

The plants will survive for more than 1 season but as practical matter they would be culled at the end of their productive period.

The stems and such are mostly water and a little bit of carbon, I guess other sources of nitrogen would have an excellent ROI (a modest amount of fertilizer vs high capital and labor costs).

I don't think hydroponics is a completely closed cycle, so there still has to be a source of nitrogen/ammonia

https://en.wikipedia.org/wiki/Nitrogen_fixation

which is ultimately very energy intensive

https://en.wikipedia.org/wiki/Haber_process

That was an enlightening read! I had no idea that humanity was so dependent on one process for so much of its essential existence!

If you think about the context in which we are operating though (desert with a lot of sunlight) it might be possible to colocate a solar powered reactor producing all the ammonia required for the hydroponic farms in the desert. This is just handwaving though: it seems like apart from electricity, the next biggest input is natural gas. While this may not be a problem in, say, Saudi Arabia, probably would be in Namibia.

With cheap enough power you can just tear the nitrogen out of the air.

https://en.wikipedia.org/wiki/Birkeland%E2%80%93Eyde_process

Hmmm I wonder if there would be a way to also grow green beans / soy beans, which always deposit nitrogen as a byproduct of their own growth. I have a mini urban farm in my teensy Chicago back yard and Rotate beans, cucumbers, and tomatoes to ensure the soil contains the right nutrients.

Have a look at this link, which I think I found on HN sometime ago. Hydroponics and fish working together in Detroit. www.modeldmedia.com/features/indoorurbanagriculture052014.aspx

or add an aquaponic cycle to solve the nitrate side of the equation (and yield fresh fish, to boot)

I added this link earlier which is following this idea, its a great story www.modeldmedia.com/features/indoorurbanagriculture052014.aspx

I love Detroit :D (btw Tilapia are illegal in Australia, they're extremely invasive, but there must be a local anlog)

In general the plant is discarded once a year. The growers normally get seedlings from a specialist that grows from seed.

The tomato plan contain mild toxic content, and is quite smelly so not even goats seem happy to eat it. Not sure what they actually do with composted tomato plants.

https://en.m.wikipedia.org/wiki/List_of_poisonous_plants

Leave it long enough to grow it into more tomatoes.

Tomatoes are ridiculously easy to grow from seed. If you let any tomatoes fall to the ground you are guaranteed to spend every year forever after dealing with hundreds of tomato plants.

Until you've got enough leaves and other detritus, there won't be any ground.

I hobby garden and also grow greens hydroponically. Greens are > 95% water weight. I think tomatoes aren't far behind.

when I first started with hydroponics I was amazed at how little fertilizer/nutrients needed to be added to the system to produce the volume I was producing.

I think with traditional farming a lot of fertilizer is lost to the environment which isn't so in closed hydroponic systems.

> I think with traditional farming a lot of fertilizer is lost to the environment which isn't so in closed hydroponic systems.

Do you have a cite on this for further reading?

https://en.wikipedia.org/wiki/Dead_zone_(ecology)

Among other factors, fertilizer runoff is a studied cause of substantial ecological effects. There's a huge rabbit hole to start you off.

I'm looking for something more quantitative.

I am also looking for someone to spoonfeed me information on random topics that momentarily take my fancy. Let me know if you find someone like that. I want to be their friend.

Most of the nutrition comes directly from seawater if they're smart, see SEA-90. I use it for most of my hydroponic plants.

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