Many people worry that our soil is depleted of nutrients and thus our produce is less nutritious than it used to be—and no wonder, given the heaps of confusing data and mounds of misinformation out there about soil nutrients.
The fertility of the soil, determined by the amount of nutrients in it, is a matter of intense concern for farmers, governments, and scientists, since it controls crop development and agricultural yield.
As they grow, crops remove soil nutrients (minerals), so replenishing them has always been an essential part of agriculture. Fertilizers are used to replace minerals, and many other methods, including crop rotation, can improve and maintain soil nutrients and quality.
Plants won't grow properly in nutrient-depleted soil. Vitamins are created by the plants as they grow, but minerals must come from the soil. If these soil nutrients aren't there, the plant droops, fails to flower, and may die. Or the plant may simply yield fruits or vegetables that can't be sold because of poor appearance.
Is Our Soil Depleted of Nutrients?
Some studies have found small declines in certain minerals in various crops over recent decades, while others have not. It's hard to know about longer-term trends, since we don't have records of nutrient content in fruits, vegetables and grains from a century or two ago. Based on what we know, however, it's unlikely that nutrient levels in produce and grains have changed very much.
Nutrients can vary from one batch of produce to another, depending on the region, climate, farming methods, time of year, how long the plant had to grow and how it was handled, and other factors. Moreover, historical comparisons are hard to make, largely because we cultivate many different varieties of fruit, vegetables and grains than we used to.
Often plant varieties are chosen because they grow faster and yield more, and that may reduce the nutrients in soil that end up in produce. On the other hand, food scientists have enhanced some produce nutritionally: carrots, for instance, supply much more beta carotene today than they did 30 years ago.
Nutrients in Organic Fruits and Vegetables Versus Conventional Produce
The notion that soil depleted of nutrients is yielding less nutritious produce is often cultivated by people selling dietary supplements. Advocates of organic produce also sometimes encourage this idea by saying that organic is more nutritious because of the soil nutrients.
Organic agriculture may be better for the environment, but most research has failed to find significant nutrient differences between organic and conventional fruits and vegetables.
Originally published in The University of California, Berkeley Wellness Letter (January 2011)