A good friend recently sent me a note that there is a story in the current Mother Earth News concerning the serious decline of nutrients in vegetables. Loss of nutrients in vegetables isn't news to me because I have been long aware of the published (and hard to find) data by the USDA on the declining nutrients in crops since the 1950's/1960's. (I used to have the USDA chart on my computer, but I lost it when the last hard drive died, and now it is not easy to find.)
Several "causes" have been cited in the research literature, ranging from overall loss in our soil nutrients, to the specific varieties chosen to plant. It certainly appears true that veggies remove micronutrients from the soil which are never replaced by the additions of just the popular NPK.
However, the loss of nutrients by the "choice" of planted varieties has me stumped. From what I read, some varieties that are chosen to grow quickly with a minimum of amendments to the soil might indeed result in a great crop of pretty and marketable produce, but lacking on the nutrition scale. Personally I am more inclined to believe the soil deficiency idea.
Taking statistics from the USDA comparing a tomato in 1963 to a tomato now (2008) shows that 100 grams of 'fresh' tomato has:
30.7% LESS Vitamin A
16.9% LESS Vitamin C
61.5% LESS Calcium
11.1% LESS Phosphorus
9% LESS Potassium
9% LESS Niacin (B3)
10% LESS Iron
1% LESS Thiamine (B1)
65% MORE Lipids (fats)
200% MORE Sodium
Vitamins E and K are not measured, nor are essential micronutrients like molybdenum and selenium.
Broccoli has lost 45% Vitamin C.
80% of the tomatoes grown in Florida now comprise just 5 varieties, and one of those 5 counts by itself for 35.9% of all tomatoes (the variety is Fla. 47).
In the last 50 years, the Canadian potato has lost 100% Vitamin A, and 57% Calcium, 50% Iron, 50% Riboflavin (B2) and 18% Thiamin.
So, its not just Red Tennis Balls that are nutritionally deficient...
I've been working on increasing nutrient density (measurements aka Brix, and also taste in the veggies... the better the taste, the higher the nutritional value) in my own garden for 4+ years now and I still don't have a good handle on it, although my results are getting better. I DO believe that sufficient micro-minerals, good compost and an excellant microbial population are a big part of the equation. I hope to have some increased positive reports this coming gardening season.