soil depletion/nutrition

[billydkid]

This is another of the wide variety of issues I don't really understand. The argument I've heard to debunk the idea that our farm land is depleted nutritionally is that the plants wouldn't grow if the soil was depleted. My question is this: are the same nutrients the plants need to grow necessarily the same nutrients which make plants nutritious to eat? Do the plants pick up these nutrients incidentally or is the fact that the plant grows at all proof positive that they contain the nutrients we need? Can someone clarify this for me?

[fuelair]

Fast: any nutrients plants take in from soil are removed from that soil and must be eventually replaced naturally or artificially if new plants are to also contain those nutrients. If enough nutrients are removed, eventually most plants won't grow and develop naturally - and even if they appear to we won't be getting expected amounts of the nutrients we are expecting (depending on soil iron content, for example, you can get lots of iron in a serving of spinach or very little iron in the serving of spinach - nutrition guidlines assume average amounts of the things each veggie/crop normally makes available - the key word is assume).
To be more specific to your question: plants do not "need" all the things they absorb from the soil (certain plants are even used to absorb environmental contaminants/poisons because they can - but they don't have to to grow). If the arguments are about the "dangers" of artificial fertilizers, they are bogus - but if they are pointing out that some farming methods are causing lower amounts of nutrients to be in the crops - it is possible - however, you should be aware that many of these claims are based on serious miscalculations of nutrient contents of crops made around 60-70 years ago by USDA people (IIRC) and the appearance of a drop is not real as the figures were very inflated at the time (a factor of at least 10 IIRC). Hope this helps - and I teach science and have no connection with fertilizer sales or farming - except eating products of the latter.

[blutoski]

This is another of the wide variety of issues I don't really understand. The argument I've heard to debunk the idea that our farm land is depleted nutritionally is that the plants wouldn't grow if the soil was depleted. My question is this: are the same nutrients the plants need to grow necessarily the same nutrients which make plants nutritious to eat? Do the plants pick up these nutrients incidentally or is the fact that the plant grows at all proof positive that they contain the nutrients we need? Can someone clarify this for me?

Good question. I think we're two conversations removed from the claim. I would want to ask: "what nutrients, exactly?" and then test the actual claim. Right now, it's kind of vague.

The short answer is: you've got a point that the fact that the plants are growing is not proof that they are nutritionally sound. Three obvious objections are: 1) through the wonders of selective breeding, they're bred to grow in nutritionally deficient environments, and 2) regardless, we will be adding basic organic fertilizer to the soil, but rarely minerals, which may be the 'nutrients' in question, and 3) I have read a claim that accelerated growing timetables means the plants grow larger, faster, but do not have sufficient time to absorb nutrients the way that their slower-growing peers do.

So, I would say that the counterargument is indeed weak.

But so's the original claim!

The best way to counter the original claim is to ask for an example 'nutrient'. The second part of the question is: is this nutrient's quantity diminished to the point where there is actually an impact on human health? eg: I have seen examples of reduced Mg in non-ogranic fruit. We're talking picoograms of difference, here, nothing relevant. So, eat an almond instead, you know?