Remember that the reason we use so much land is because that's the cheapest way to grow food. We could grow more food on less land by farming more intensively. We don't because that would make the food more expensive. At an extreme, a greenhouse can increase yields 100x but at an increase in costs of 10x.
From various reports lately, I don't have links handy but I've seen them shared here on HN, it is generally accepted that the nutritional value of the food is declining. This has been primarily attributed, from what I remember, to the condition of the soil. So, if we start producing everything in a greenhouse, won't that impact nutritional value as well.
Healthy soil can be cultivated at scale, so if quality is the top priority that's not an issue. At least two major factors are at play:
- soil usually doesn't get time to recover and gets fertilized every year, nutrition can't build back up because of worsening chemical conditions due to monoculture and salts -> simply less nutrients are available to the plants with each cycle
- plants get bred to maximize yields, leading to first and foremost bigger plants, other factors (like nutritional value) are not priority #1
>Healthy soil can be cultivated at scale, so if quality is the top priority that's not an issue.
The larger issue is that consumers have no way of assessing the nutritional value of the items they're purchasing at the point of purchase. Cost is mediated on the basis of weight, which results in water-rich, nutrient poor, taste-poor produce. Saline injection into meat is another similar issue.
How do we make growing nutritional food profitable? Foods that can be sold on the basis of nutrient specific benefits, like Golden Rice or Vitamn D enriched milk can be marketed and sold on that basis, but comparing two beefsteak tomatoes grown in differing soils is not possible at present at the point of sale.
Typical food certification strategies, such as Organic, DOP, AOC, and other regional growth indicators don't seem to fit the bill. It's also unclear whether or not there is a market for inspections on the basis of nutritional value - from an organizational standpoint, it shouldn't be too difficult to have an inspector randomly audit crops and send samples to a lab to be HPLC or Mass Spec'd, but whether or not another certification mark changes buying patterns is unclear.
In Japan they have handheld machines that measure sugar content and acidity of fruits,[1] because fruits are used as gifts and you want to make sure it's a good one. How can we get fruit manufacturers to start sorting their fruit by sweetness?
They start around $1000 because it's a niche market. They appear to be infrared spectroscopy based which isn't too complicated, I was thinking about making an open source version. Should only be like $30 in parts. Would people buy this to test their produce before they buy?
[1] Called non destructive saccharimeters
Edit: actually it looks like they measure infrared polarization, not spectral absorption
Taste generally tracks with nutrition in non processed foods. If that could be validated, then we have a win win— and then needs new ways of marketing/branding higher taste options
I suspect that “if” will be more difficult than just measuring the vitamin and mineral content of random samples of the produce directly, but even if it isn’t, taste would rapidly be another flawed proxy: https://en.m.wikipedia.org/wiki/Goodhart%27s_law
(I’d argue that taste is already an example of Goodhart’s law, and that this is why fast food is popular despite being objectively bad).
What about a handheld scanner using smell to distinguish good from bad. As long as food isn't bred to smell certain ways that can't be distinguished from good, it should work fine.
>Healthy soil can be cultivated at scale, so if quality is the top priority that's not an issue.
Healthy soil can only be cultivated at scale with the aid of petrochemical byproduct fertilizers, which are not likely to be a long-term feature of our agricultural system.
The fertilizer that is derived from fossil fuels is ammonia (and nitrate made from ammonia by partial oxidation). More precisely, it's made from hydrogen derived from steam reforming of methane. But any source of hydrogen would do, including electrolysis with renewable electricity. There is nothing essential about fossil fuels for industrial agriculture.
It should also be noted that the total energy consumed in growing food in the US (ignoring sunlight absorbed by the plants) is less than the energy used to COOK food in the US. It's roughly 1% of the total energy used by the US.
The petrochemicals can be synthesised from CO2 and water with known methods. While nobody bothers with this right now, SpaceX basically has to make this economical as one sub-goal of their Mars colony, so I expect it in a decade or two, well before we run short of natural petroleum.
I’m more concerned with the long-term need to recover the potassium and phosphorus that washes into the ocean, which, despite still being theoretically solvable, is not currently economic enough to bother with even for the gold and uranium that’s also in the seawater.
It's never seemed to me that this whole "worse soil -> less nutrients" postulate makes sense on its face. There are, roughly, four categories of nutrients:
- organic macronutrients, which we'd definitely notice if they weren't there
- organic micronutrients, which are generally carbon compounds, but carbon doesn't come from soil, it comes from the air
- electrolytes, which do come from soil, but are always replenished with fertilizer, because plants need them too
- inorganic micronutrients, essentially transition metals plus selenium and iodine, which are present in utterly tiny quantities in food (you need about half a milligram of selenium per day), and could certainly be replaced by fertilizer if we even tried, or easily supplemented. Speculation: manure could work well.
- (extra) that wacky little devil cobalamin, which is both organic and a transition metal (cobalt), but doesn't come from plants anyway
Now, I could certainly see some kinds of farming techniques impacting the nutritional quality of plants. If you can increase the water content of your broccoli ceteris paribus, you sell more broccoli but the concentration of vitamin C goes down. I could also see impacts on the physical properties (compaction, grinding) of soil leading to worse long-term crop yields. But in order to convince me that soil changes are going to impact the vitamin C content of orange juice, when the constituents of vitamin C come entirely from water and air, you need pretty strong evidence.
Fairly easy answer to this. If I took a orange tree and only fed it water and air. Would it produce oranges with vitamin c? The answer. No. Because the plant requires far more than just water and air in order to run all the other systems within itself to make that vitamin c production happen. If you take away certain elements in your soil, your going to affect aspects of that plants health that in turn affect its production capacity. If you provide most nutrients for a plant sure it will produce fruit. Will that fruit be as good as fruit from a plant with all the nutrients? No, no it will not.
As far as I remember from the last discussion on the matter the effect is overblown. Nutrient decline for modern techniques and soils is around 7% from baseline.
To recap, there are declines up to 30% in certain nutrients for certain vegetables. This seems to be mostly down to farmers choosing varietals that grow faster and handle transport better over time.
Personally it's still my opinion that this is no big deal. Even if, say, oranges are lower-quality than a century ago, they are now cheap, easy to obtain and available year-round. You might have to eat four oranges instead of one for whatever nutrient allotment you desire but...that's a heck of a lot easier than it was for our grandparents. As long as people aren't eating mainly combinations of flour and oil, they'll be fine.
That article is quite odd. It does not misrepresent the studies that it references. This [1][2] is the primary one, the 2004 paper from Davis et al. But the paper makes it very clear, as does the article in its discussion of the paper, that the main culprit is believed to largely come down to breed selection. It does consider soil quality and ultimately dismisses it as the main variable:
"The apparent overall decreases for some nutrients are interesting and potentially of concern, but like Mayer and Johnson,
we urge caution about their interpretation. Mineral decreases
are popularly predicted for, or blamed on, mineral deficiencies
in soil and fertilizer [5], but without sufficient consideration of
contrary evidence and other possibilities.
[Snipping various scientific evidence they mention]
Factors other than soil mineral concentrations seem to have primary control of food mineral contents for
the foods and minerals studied here. (The minerals I and Se are
well known exceptions to this rule.) In the case of Fe, depletion is
never an issue; instead, the issue is the ability of the plant to
acquire the Fe that it needs. The fraction of soluble Fe in soils
may be only about 10^-13 of total soil Fe."
In general, there seems to be an inverse relationship between nutrition and yield: higher nutrition + lower yield, or lower nutrition + higher yield. It's not hard to guess which we pick. But then the article (similar to another published in Discover magazine) focuses entirely and exclusively on soil quality as the primary issue.
I'd strongly argue against that. A lot of people somewhat mindlessly consumer fruit and fruit juice 'because it's good for you' which is a reasonable proxy for high levels of things like Vitamin C.
And fruit is in general very good for you, but of course it's also quite high in calories. A single navel orange has upwards of 70 calories [1]. So 2 oranges ~= 1 can of Coke. And fruit juice is even worse. A plain cup of orange juice has 112 calories. If somebody buys some form of it that's been sweetened or otherwise mixed, you can easily end up with your OJ having more calories than a Coke.
People can easily speed their way to obesity by eating things that they think (and are) 'good for them' without really appreciating how many calories they're consuming. Similar to how things like vegans can easily end up consuming way too many calories when doing things like using peanuts as a protein source. An 80kg man needs around 64 grams of protein a day. 64 grams of protein from peanuts (to take things to an extreme) would be more than 1400 calories. And that's from raw unseasoned peanuts, which have the best nutrition:calorie ratio.
The biggest factor is likely just reduced infant mortality. Today when we say today that somebody has a life expectancy of e.g. 80 years, then it does mean you can expect people to start dropping of various causes around that age, give or take a bit because infant mortality is approaching zero.
In the past infant mortality was extremely high, with frail infants invariably ending up as dead infants. And so in the past if you looked at somebody who was 15 years old, it's very likely that he'd live to roughly the same age as somebody today. It's not like he'd just start dropping around age 40. It was more a mix of people living to 5 years old and people living to 80 years old. Take the founding fathers as a random example:
==========
John Adams - 91
Benjamin Franklin - 84
Alexander Hamilton - 49 (killed in a duel)
John Jay - 84
Thomas Jefferson - 83
James Madison - 85
George Washington - 67 (speculation he may have been killed by a common medical practice of the time - bloodletting)
==========
Interestingly enough this goes all the way back to Ancient Greek times where you may be surprised upon some brief research to see how long any Greek you know of likely lived to, in spite of having effectively zero medical knowledge and hygienic practices such as shared butt sponges (in lieu of toilet paper) at the various public toilets. The reason I more contemporary samples is because one can reasonably argue a survivorship bias in the Ancient Greeks. Would you know of Philosophartes today if he had died when he was 40? Probably, but I can't prove that. The founding fathers though were all relatively young when their names were inscribed into history.
So how do you explain that life expectancy at for instance 50 years old keep increasing? For instance in my country (CH) life expectancy at 50 years old for a man was 26y in 1980, 29.5y in 2000 and 32.5y in 2020.
People keep saying that infant mortality is the explanation but this is only valide for life expectancy at birth. Life expectancy at all ages as been increasing.
Infant life expectancy describes the huge changes. We went from life expectancies in the 30s not that long ago, to life expectancies in the 70s, largely due to it. The smaller changes since are going to be from many reasons that will also often vary heavily between regions. Unfortunately I lack the knowledge to even begin to intelligently speculate about the reasons for China's improvements.
More doesn’t account for nutritional deficiency. If zinc is missing in a foodstuff, it requires supplementing with other foodstuffs, not eating more of the same foodstuffs.
Nutritional drops have been minimal (see other comment references 7%) and considering most Americans don’t even get the minimal servicing of fruits and vegetables I’d worry about that first.
"nutritional value" isn't a scientific term so you're going to have to define what you mean by that. Crops have been in fact getting more and more energy dense over time.
It's not just space, global warming could lead to a complete ecosystem collapse (think Mars). We may need to move everything into climate controlled environments.
Nutritional decline of actual fruit and vegetables or the nutritional decline of food as is consumed by humans?
I don't think we are seeing the former while the later is how you use the former for the production of actual food that is consumed.
Converting fruits into smoothies makes them retain mostly only sugar, while vegetables (and fruits) under thermal treatment loose a lot of nutrients like fiber and vitamins.
I think the parent might be slightly off the mark or simply is lacking detail.
One concern in nutrition is separating fruit juice from fruit pulp. You probably wouldn't eat three oranges in a sitting without feeling full but you can certainly drink three oranges' juice. That's the number of fruit needed to make a cup of orange juice.
If you're adding juice to a kale smoothy it's more complicated. At a certain point of extortion, refinement, and concentration that juice can become a proxy for simply adding cane sugar.
If you're blending your fruit and eating the pulp then there is no change.
I can see agricultural land going down even further in the future as techniques, incentives, and people dynamics change.
How much of what we farm is really just 'superficial agriculture' and not 'survival-driven agriculture'?
For example: gigantic monoculture fields of corn in the midwest US, groves of almonds and grazing crops in California, huge amounts of grasslands for beef. (I'm sure there's more examples too)
It just seems like many of the ways agriculture operates doesn't make sense from a needs-based perspective and certainly not from a nature-enhancement perspective either. Farmers just do their job of growing, and then money does its job of convincing.
Corn makes up more than 10% of global food production. A significant fraction of the world would not 'survive' if those fields of corn suddenly disappeared.
A better example would be specifically corn used for ethanol because driving a car is not essential for survival.
The other two examples seem valid. Replacing part of your meat consumption with corn would reduce the required agricultural land.
An interesting quote which echos what you're saying here:
> That means that table corn, carrots, cabbage, apples and broccoli are all examples of what is called, paradoxically, “specialty crops” — and they largely don’t get the same support as the heavily subsidized industrial crops.
The absurdity here is that "specialty" crops are what you might call "food". Most corn is "what my food eats".
If survival was important, people could switch trivially. I would take a 99% vegetarian diet in exchange for not dying. Problem is that the costs may be collectivized, and weighted towards future generations.
Lots of ways. We can live with much less sugar in our food. One example: sugarcane. According to the (UN) FAO,
"The present area of sugarcane (Saccarum officinarum) is about 13 million ha with a total commercial world production of about 1254.8 million ton/year cane or 55 million ton/year sucrose. (FAOSTAT, 2001)." [https://www.fao.org/land-water/databases-and-software/crop-i...]
That climbed to 1.9B tons by 2020. [WP ... 40% in Brazil] And 13Mha = 130,000 km^2 > 50,000 sq.mi. About the size of Iowa. And then, there's almonds.
Only 1% of the corn grown in the US is "sweet corn", i.e. corn that's meant for direct human consumption on the cob or canned. The other 99% is "field corn", and that gets used primarily in livestock feeds and ethanol (the latter being a subsidy boondoggle of the highest order), and industrial manufacturing (base starches). A sliver also gets used for corn syrup.
The error being made is assuming that corn cultivation being significant to global food supply means that corn is being cultivated primarily for food.
I've read that biofuels are a waste. As in, if we replaced all the cars and trucks with electric ones, we could power them fully with solar energy deployed on the land used for the 5% biofuel... And use 90% of the reclaimed land for reforestation. The math seemed reasonable. But obviously doing this wouldn't work politically (even if we could make all those EVs and solar panels in the first place).
California grazing issue is much more complex than consumer preferences for beef. Humans have basically destroyed the grazing populations that used to live there, including Buffalo. If you take the current land used for grazing and just stop, you’ll significantly increase fire risks as nothing else will eat all that brush and it’ll just collect. Go look around city borders where a lot less cattle grazing goes on - those hills have been stripped of forests and are just a pile of brush waiting for light up.
The entire premise of that thread is questionable. Sustainably managed rotaional grazing pasture fed beef is a grassland ecosystem, quite similar to what much of the United States looked like when buffalo roamed before european-heritage settlers.
Destroying forests to make pastures is environmentally destructive, but a large portion of our country can be utilized as pasture while maintaining an ecosystem not unlike how the land was before capitalism transformed it.
FTA “ improvements in crop yields, agricultural productivity, and dietary choices are so important.”
and the biggest one imo is dietary choices. Our meat consumption has lead to pasteurization of forest land to raise and feed the huge amount of livestocks needed to satisfy our meat craving.
In the US, at least, we could keep our meat consumption quite high while still grazing lots of cattle. There are around 90 million cows in the US right now, and pre-1800s there were around 60 million bison in the US. Land and pasture management is important, but it can be done well. Check out Alexander Family Farm in CA for a great example.
We're not going to turn marginal grasslands into crops for human consumption, but using cattle to turn inedible grass into calories for human consumption is possible while maintaining that land as it was when bison roamed through it.
I also don't think that the US, for example, has to manage its land the same ways as other countries. If the US can effectively manage pasture and raise lots of cattle to eat, then we should be able to do that, and if other countries can't, then they should manage their land in a way that is optimal for their country. The US has a lot of grass pasture land that evolved over time to support the massive number of ruminants that roamed the US in the not too distant past.
Maybe the US should stop exports of beef and dairy and just focus on feeding its own people from well-managed land. But that would not be very popular, especially with our cattle industry.
While the many types of forests (deciduous, coniferous, rain, etc) dominate a lot of land on earth, there is still many types of plains, chaparral/savannah, deserts, mountain, tundras, etc.
> The source of his worry is a huge trade deal being negotiated by the European Union and the four Mercosur members Argentina, Brazil, Paraguay and Uruguay — an accord whose signature seems closer than ever.
> The new imports would represent just one percent of Europe's total beef production, and 4.5 percent of France's output.
So the deal hasn't been signed and wouldn't represent much.
> Issues à près de 92 % de l’Union européenne, les importations de viande bovine chutent de 16,8 % sur un an, pour atteindre près de 283 milliers de tec en 2020
Which rougly translates to "92% of beef imports are coming from the UE. They fell by 16.8% to 283k tec in 2020".
There's a total in "tableau 2", page 3. 28.4% of the total meat is imported, 18.9% for the beef. The total non EU beef is thus 8% (100% of total beef imported - 92% of UE beef) * 18.9% (percentage of imported beef). Rounded up, it's 1.6%. I would hardly call that "outsourcing their diets and problems" and "pulling a lot of their beef from South America". More than 80% of the cattle eaten is localy raised, less than 2% comes from outside the EU.
South American beef is not a thing in France. We surely have plenty of other issues, but South American beef is not one of them.
Imports exist, and France is a major importer of meat. Meat production has become less land intensive compared to 200 years ago, but it is by far the worst way of producing food if you compare calory intake to land use.
> Meat production has become less land intensive compared to 200 years ago, but it is by far the worst way of producing food if you compare calory intake to land use.
Most meat, at least in France, is raised on land that couldn't support other kind of agriculture. The calorie intake of that land, without cows grazing on it, would be 0.
I doubt so, farmers in my village in France never take their cows out of the barn. They feed them with dry grass and fermented corn (ensilage) they grow.
Cow grazing is a thing of the past unless you do milk for AOP cheese or premium meat. By the way cheap beef in supermarket is actually old milk cow
No European country does really. Nor do Australia and New Zealand to my knowledge. That’s why the beef tastes so much better. Cattle that are grass fed taste very different.
Yes. You asked about feedlots. Europe pretty much doesn’t have them, as I said. Note that beef cattle are 80% grass fed according to the document. Dairy that are eventually eaten eat less grass, 2/3.
I was talking about more than feedlots, I was talking about grass-fed cattle vs. not grass-fed cattle. Do you really think it matters if a cow eats grain in a "feedlot" instead of on a "farm"? I sure don't.
The lifecycle is more complex than this. Slash and burn agriculture is used to squeeze a few cash soybean crops out, this requires specific GMO soy, and these are 90% sold to China to fatten pigs.
When the land is only suitable for grass, it's grazed for awhile, after which it's basically desert.
South America also has some of the richest cattle land in the world in the Pampas, which has sustained beef production for hundreds of years on land which is otherwise unsuitable to food production.
Pressure on one company could stop the conversion of rainforest into soybeans. This doesn't solve the problem in a single stroke, nothing can, but it would help, and it doesn't require influence over the government of Brazil.
Yes, let's blame the consumer. First of all, the consumer has no idea how their specific spending habits contribute to an issue. For instance, an educated consumer (many consumers are not educated btw) might understand that eating meat causes deforestation, but they have no way of knowing if their specific purchase is contributing to that. Second, blaming the consumer makes any solution almost impossible because organizing a very large group of disinterested people is very hard. It would be much more effective to regulate the relatively small number of meat producers that are perpetuating deforestation and let the market work out decreasing consumption through increased costs.
Yes, let's. I don't think an argument can be held against this. As a meat eater, I understand I'm the driving force of this issue. It's an inconvenient truth, but it is the truth nonetheless. I'm rooting for alternatives like lab-grown meat to thrive, but no amount of wishful thinking allows me to skirt the fact that eating less meat would probably be not only good for the planet, but specifically for my own health.
> the consumer has no idea how their specific spending habits contribute to an issue
Let me point it out: in the developed world it's almost 100% guaranteed that it contributes significantly. You have to go to pretty far edge cases to find really sustainably produced meat. A case can be made that not all industrial farms contribute to deforestation per se, but they are all part of a system that has a high cost for our environment. Deforestation is bad, but it's not –and should not be– the only issue.
> As a meat eater, I understand I'm the driving force of this issue.
How did you come to that understanding? Did you dedicate your free time to studying the impact of meat eating, or was it part of your legally mandated education? A lot of people scrape by, barely able to make ends meet. They have children that require attention, or problems that require immediate action. They may have debts to pay, and no social safety net to help. At a fundamental level, they may have poor critical thinking skills. It's not realistic to expect every consumer to take the time to understand the consequences of every purchasing decision.
> A case can be made that not all industrial farms contribute to deforestation per se, but they are all part of a system that has a high cost for our environment.
But the package says it was humanely raised by family farms? Your trips to the grocery store are going to take a very long time if you need to do a supply chain analysis of every purchase.
If a person cuts down a tree for profit, and the removal of that tree is problematic, then that person is to blame. It doesn't make sense to blame someone many steps removed from the crime just because they, in a very indirect way, provided a very small incentive to commit the crime. The impact of the individual's consumption on the entirety of the industrial farming system is so small that, even if the individual consumer were to blame, they would be guilty of nothing more than the tiniest infraction. The issue with industrial farming arrises from the collective sum of demand, and thus requires a collective solution, i.e. centralized regulation.
But the parent commenter has an important point that should not be dismissed. It is far more effective to regulate/improve centrally at the producer side rather than "wait" for the goodwill of consumers.
You can't flood the world with cheap unsustainable meat (or other products), next put a far more expensive sustainable option next to it and think all of this will just magically play out.
Ideally, there should be no unsustainable goods being offered at all. The very word unsustainable pretty strongly suggests that ending the practice is a must.
Greenhouses are amazing. One of the top agricultural exporters in the world is the Netherlands. That shocked me when I discovered it. Part of the reason is fertile soil and dependable rain. But a huge component of how they can do so much with so little land is greenhouses.
It seems like something we could stand to invest a lot more in as a global civilization. An understated benefit is making the food supply more robust to volcanoes, asteroids, and nuclear winters.
I come from a family of farmers since centuries, in Southern Europe. I am the owner of several large plots of land and I helped my family when I was a kid.
Growing food in greenhouses makes food cheaper than growing food outside greenhouses. Problem is quality. E. g. a tomato grown in a greenhouse does not taste as good as a tomato grown outside. In fact, the greenhouse tomato hardly has any taste.
Another problem is organic, eco-friendliness and all of those "luxuries of the first world": when growing in greenhouse, you'll have to use pesticides and all of those things that improve yield and keep plagues at bay. But then you are no longer ecological so some markets (e. g. Germany) close for you.
Also, this whole thing about "peak agricultural land". Bullshit. Really. There's plenty of unused agricultural land. The main problem with agriculture as of today is prices of sold goods vs cost of production, and that's only because of globalization, cheap transport and cheap labor in third-world countries (Africa, South America). E. g. where I grew up, there were big extensions of almond trees. Yet already 30 years ago, it was cheaper to bring almonds from California than grow our own almonds here! That crop is almost gone now, except for people (like me) who still have some almond trees for our own consumption (not to sell).
And the actual problem will happen in a few years, one or two decades at most: most of the sons and daughters of farmers went to university or vocational school, and now they have other jobs. Not farming. What will happen if globalization reverses (like it seems to be doing since COVID-19 started)? or if transport costs so much that growing locally starts to make economical sense again? We will have lost that knowledge and skills about agriculture. My only hope is I am seeing a few of my school and university mates, who studied Economic Science, Psychology, Electric Engineering, Civil Engineering, etc and became so fed up with those jobs, that they went back to agriculture (and they are making money because they have an analytical mind and they know what to grow, when and who to sell to, and first thing they do is they have a "business plan" for their lands and crops). Something like what happened in electronics.
As a rule of thumb, you don't do extensive agriculture in a greenhouse. You don't need to because as I said, there is plenty of land available.
However, it is definitely possible and there are many studies on that since at least 20 years. The 2 big cons are:
- Energy costs (artificial lightning)
- Harvesting is a lot more difficult (at least with the current technology)
BTW, one more thing I forgot in my earlier comment about why agriculture has been mostly abandoned in Western countries: phytosanitary products (e. g. pesticides). Many phytosanitary products that are no longer (or were never) allowed in the US, Canada, Europe, etc are perfectly legal in Africa, South America, Asia, etc so their yield is a lot higher, thus again contributing to smaller production cost.
So a 1000x increase in total cost? That doesn't add up, it doesn't cost that much to use your own greenhouse, I can't imagine something like that wouldn't benefit from economies of scale.
The extreme isn't too important and highly dependent on the plant but it still can reach 10x the efficiency on average. There are some plants that don't do well in a greenhouse since they need a period of dormancy.
Power consumption is also a factor. Without fans the humid environment is prone to fungal infections and certain pests can spread pretty quickly too.
Overall it is a benefit since it simply allows for climate control. But you also have to heat it in winter since the plants will be very susceptible to the cold in their pots. Still, greenhouses are barely an option in the hotter climates since the power consumption would be insane.
And nobody would grow potatoes in a greenhouse because that would be extremely labor intensive.
I've visited a very advanced tomato greenhouse. They have a heliostatic solar field and tower that provides heating for the greenhouses plus fans for cooling, and desalinates water to irrigate.
The tomatoes grow in their substrate on top of big cooling/heating pipes that can be easily regulated. There's automated ventilation at the top of the greenhouses. They release wasps inside the greenhouse to control pests. Through summer, they spray the greenhouses with a chalky material to block some of the light.
Picking carts can self-drive themselves via guiding tracks embedded in the concrete flooring. It's all very clever, the plants are insanely productive and the produce tasted good to me.
Meanwhile my homegrown tomatoes are a constant battle on every front (heat, water, pests, etc).
For greens, an conventional farm is $0.65/lb and a greenhouse is $2.33/lb.
> Assuming a 40-45% gross margin for a typical supermarket produce department, retail prices for greens would need to be approximately $1 a pound for conventional, $4 a pound for greenhouse, $5 a pound for vertical, and $12 a pound for container-grown. A typical head of bibb or butter lettuce weighs less than half a pound. Therefore, the lettuce can be grown in a greenhouse or vertical farm and sold at retail for $2 to $3 per head.
> Although greenhouse or vertical farming is three to five times more expensive than growing on a conventional outdoor farm, it still allows for competitive pricing to the consumer with other vegetables and sides.
The yield can go up, but the cost per unit goes up too.
You can't run a harvesting tractor through a greenhouse. So, a lot of produce from greenhouses or vertical farms (etc) ends up with a manual harvesting step.
This is why you pretty much see greenhouses exclusively used for foods which would require that manual step anyways.
Note that this is an area that is rather specialized - a pepper picking robot isn't good for tomato picking or lettuce picking ( https://youtu.be/EFC3OvkVKaQ ). Compare that to the incredibly versatile human ( https://youtu.be/oxbJVqfIK1U ).
Not just the cheapest, but the easiest: in many countries, and especially (though not exclusively) the US, the primary purpose of farming is landowning, so the primary incentive is limiting inconvenience.
Remember that the reason we use so much land is because that's the cheapest way to grow food. We could grow more food on less land by farming more intensively. We don't because that would make the food more expensive. At an extreme, a greenhouse can increase yields 100x but at an increase in costs of 10x.