6 ms·

When we say that we have a shortage of farmland, what we mean in practical terms is that we have a shortage of flat areas with good drainage to function as sola

When we say that we have a shortage of farmland, what we mean in practical terms is that we have a shortage of flat areas with good drainage to function as solar collectors. Well, it is a bit more complicated than that. A huge problem in agriculture is the depletion of soil. For example, over time intensively irrigated soil tends to become contaminated with excess salts which destroys its fertility, yet still leaves it as flat, well-drained, and sunny as ever. I completely agree, however, that the first-order consideration in growing plants is the availability of light.

DennisP 16y ago
Aquaponics actually gets you pretty close to a closed-cycle ecosystem. I read the other day about a family of four which grows all its food from an old in-ground swimming pool in their back yard. They put a greenhouse covering over it, filled a couple little ponds inside with tilapia, added vegetables and chickens. After one year they're extracting all the veggies, fish, and eggs they can eat.
- dalke 16y ago
  Potatoes give about 6 million food calories per acre. (Wheat and most other plants yield less.) Assuming 8,000 calories per day, the family would need at least 1/2 an acre to survive. An Olympic-sized pool is 0.3 acres, so it's a bit beyond the edge of possible. I doubt their pool was that large, and since most other vegetables, to say nothing of fish and chickens, are less efficient food sources, I suspect they get a good fraction of their calories from elsewhere. To check myself, this seems like a good thread: http://urbanevolution.org/thinktank/viewtopic.php?f=6&t=11 http://urbanevolution.org/thinktank/viewtopic.php?f=6&t=... . The strongest advocates for intensive and efficient agriculture say "less than half an acre (~ 0.2 hectares) can support a family of four" and "a vegan diet can meet calorie and protein needs from just 300 square metres using mainly potatoes. A more varied diet with plenty of fruit and vegetables, grains and legumes would take about 700 square metres." Say it's 2500 square meters for a family of 4 = 0.6 acres. So, no, I don't think they get most of their food from the area of their backyard pool.
  - DennisP 16y ago
    Your arguments are compelling but I'm not yet convinced it's impossible. One of their main crops is duckweed, an aquatic plant that grows very rapidly, though I haven't found specific numbers. Duckweed feeds their tilapia, which also breed and grow quickly. They say they extract eight tilapia every day, along with eggs and vegetables. Their chickens eat a lot of insects, a reserve of calories neglected by your potato field. Their website is at http://gardenpool.org http://gardenpool.org. It doesn't yet have as much detail as I'd like but hopefully more is forthcoming. Here's someone else who harvests 6000 pounds of food per year from a tenth of an acre, with 350 different crops: http://urbanhomestead.org/urban-homestead http://urbanhomestead.org/urban-homestead It seems to me that exploiting a lot of ecological niches might be more productive than monoculture. You can't extract more calories than sunlight provides (not counting insects from surrounding areas), but maybe sunlight is not the most limiting factor.
    - dalke 16y ago
      Vegetables have about 100 calories per pound. (See http://www.beyondveg.com/billings-t/cal-par/calorie-paradox1c.shtml http://www.beyondveg.com/billings-t/cal-par/calorie-paradox1... ). You can get higher by picking the right plants so let's say 300 calories per pound. At 6,000 pounds per year that's 1.8 million calories. At 2500 calories per person per day that's enough for two people for a year. For a family of 4 that's at least twice the area, or 0.2 acres needed, and likely more as the web page says their max was 6,000 pounds. It also doesn't say which plant those were, nor what the moisture content was. After all, if a watermelon is 15 pounds then that's 400 watermelons, and each one gets 11 sq. ft, but most of that is water weight. And as for the gardenpool, as best as I could tell, duckweed is 6 times more productive than corn, and tilapia at best consume 1.5 lbs to produce 1 lb of weight. Not all that weight will be edible, and corn isn't as productive as potatoes, but the numbers work out that it might be 2-3 times more productive than my potato number for the same area. However, I think the numbers for duckweed yield are in pig waste water or something else with a lot of nutrients in it, and everything is here is under best conditions, which also means a lot of care taking. Which potatoes don't need. BTW, the web site says 8 eggs per day, not 8 fish. It looks like it takes 5 months for tilapia to mature to eating weight, and 8 fish a day would mean stocking 1,200 fish at a time. What they don't say is, is duckweed the only food source for the fish or are they adding other feed? They also mentioned that they need a swamp cooler to keep the temperature in check. Assuming that's 200W average over 24 hours, that another 4,000 kcal ("food calories"), or almost enough for two people. They get that off the grid, but if they needed to provide their own fuel source for heating and cooling (tilapia can't handle cold water) then that's another factor in the energy equation. Potatoes are hardy in northern, cool climates.
jdietrich 16y ago
Of course it's a bit more complicated, but we again come back to energy - soil improvement is essentially an energy input, be it oil-derived fertilisers, organic matter or fallow.

DennisP 16y ago

Aquaponics actually gets you pretty close to a closed-cycle ecosystem. I read the other day about a family of four which grows all its food from an old in-ground swimming pool in their back yard. They put a greenhouse covering over it, filled a couple little ponds inside with tilapia, added vegetables and chickens. After one year they're extracting all the veggies, fish, and eggs they can eat.

dalke 16y ago
Potatoes give about 6 million food calories per acre. (Wheat and most other plants yield less.) Assuming 8,000 calories per day, the family would need at least 1/2 an acre to survive. An Olympic-sized pool is 0.3 acres, so it's a bit beyond the edge of possible. I doubt their pool was that large, and since most other vegetables, to say nothing of fish and chickens, are less efficient food sources, I suspect they get a good fraction of their calories from elsewhere. To check myself, this seems like a good thread: http://urbanevolution.org/thinktank/viewtopic.php?f=6&t=11 http://urbanevolution.org/thinktank/viewtopic.php?f=6&t=... . The strongest advocates for intensive and efficient agriculture say "less than half an acre (~ 0.2 hectares) can support a family of four" and "a vegan diet can meet calorie and protein needs from just 300 square metres using mainly potatoes. A more varied diet with plenty of fruit and vegetables, grains and legumes would take about 700 square metres." Say it's 2500 square meters for a family of 4 = 0.6 acres. So, no, I don't think they get most of their food from the area of their backyard pool.
- DennisP 16y ago
  Your arguments are compelling but I'm not yet convinced it's impossible. One of their main crops is duckweed, an aquatic plant that grows very rapidly, though I haven't found specific numbers. Duckweed feeds their tilapia, which also breed and grow quickly. They say they extract eight tilapia every day, along with eggs and vegetables. Their chickens eat a lot of insects, a reserve of calories neglected by your potato field. Their website is at http://gardenpool.org http://gardenpool.org. It doesn't yet have as much detail as I'd like but hopefully more is forthcoming. Here's someone else who harvests 6000 pounds of food per year from a tenth of an acre, with 350 different crops: http://urbanhomestead.org/urban-homestead http://urbanhomestead.org/urban-homestead It seems to me that exploiting a lot of ecological niches might be more productive than monoculture. You can't extract more calories than sunlight provides (not counting insects from surrounding areas), but maybe sunlight is not the most limiting factor.
  - dalke 16y ago
    Vegetables have about 100 calories per pound. (See http://www.beyondveg.com/billings-t/cal-par/calorie-paradox1c.shtml http://www.beyondveg.com/billings-t/cal-par/calorie-paradox1... ). You can get higher by picking the right plants so let's say 300 calories per pound. At 6,000 pounds per year that's 1.8 million calories. At 2500 calories per person per day that's enough for two people for a year. For a family of 4 that's at least twice the area, or 0.2 acres needed, and likely more as the web page says their max was 6,000 pounds. It also doesn't say which plant those were, nor what the moisture content was. After all, if a watermelon is 15 pounds then that's 400 watermelons, and each one gets 11 sq. ft, but most of that is water weight. And as for the gardenpool, as best as I could tell, duckweed is 6 times more productive than corn, and tilapia at best consume 1.5 lbs to produce 1 lb of weight. Not all that weight will be edible, and corn isn't as productive as potatoes, but the numbers work out that it might be 2-3 times more productive than my potato number for the same area. However, I think the numbers for duckweed yield are in pig waste water or something else with a lot of nutrients in it, and everything is here is under best conditions, which also means a lot of care taking. Which potatoes don't need. BTW, the web site says 8 eggs per day, not 8 fish. It looks like it takes 5 months for tilapia to mature to eating weight, and 8 fish a day would mean stocking 1,200 fish at a time. What they don't say is, is duckweed the only food source for the fish or are they adding other feed? They also mentioned that they need a swamp cooler to keep the temperature in check. Assuming that's 200W average over 24 hours, that another 4,000 kcal ("food calories"), or almost enough for two people. They get that off the grid, but if they needed to provide their own fuel source for heating and cooling (tilapia can't handle cold water) then that's another factor in the energy equation. Potatoes are hardy in northern, cool climates.

jdietrich 16y ago

Of course it's a bit more complicated, but we again come back to energy - soil improvement is essentially an energy input, be it oil-derived fertilisers, organic matter or fallow.