"A landmark study on the topic by Donald Davis and his team of researchers from the University of Texas (UT) at Austin's Department of Chemistry and Biochemistry was published in December 2004 in the Journal of the American College of Nutrition. They studied U.S. Department of Agriculture nutritional data from both 1950 and 1999 for 43 different vegetables and fruits, finding "reliable declines" in the amount of protein, calcium, phosphorus, iron, riboflavin (vitamin B2) and vitamin C over the past half century. Davis and his colleagues chalk up this declining nutritional content to the preponderance of agricultural practices designed to improve traits (size, growth rate, pest resistance) other than nutrition."
The Organic Consumers Association cites several other studies with similar findings: A Kushi Institute analysis of nutrient data from 1975 to 1997 found that average calcium levels in 12 fresh vegetables dropped 27 percent; iron levels 37 percent; vitamin A levels 21 percent, and vitamin C levels 30 percent. A similar study of British nutrient data from 1930 to 1980, published in the British Food Journal,found that in 20 vegetables the average calcium content had declined 19 percent; iron 22 percent; and potassium 14 percent. Yet another study concluded that one would have to eat eight oranges today to derive the same amount of Vitamin A as our grandparents would have gotten from one.
What can be done? The key to healthier produce is healthier soil. Alternating fields between growing seasons to give land time to restore would be one important step. Also, foregoing pesticides and fertilizers in favor of organic growing methods is good for the soil, the produce and its consumers.
The article above touches on a few important points, first agricultural practices.
Mass produced foods are grown for their size and yield, not necessarily nutritional value.
This is one of many reasons we work to grow so much of our own food.
Second, Feed the SOIL to feed your plants.
There are so many organic options to feed your soil. We don't need synthetic, chemical fertilizers and pesticides.
Mycorrhizae is a fungi that has a beneficial relationship with a plants roots. When Mycorrhizal fungi comes into contact with a plants roots it begins to colonize, or multiply, on the roots and begins to spread out into the surrounding soil.
Lastly, Heirloom Seeds are unaltered and open-pollinated. If you are looking for seed varieties that have withstood the test of time, choose Heirloom Seeds.