Why you should care about dirt: Connecting soil and our health

By: Kaylee Helfrich

When my family moved to Ohio, my father was excited.  Not because of the new job or larger house, but because we now lived across the street from a farm.  My father was thrilled that we could ask our neighbors for manure from their animals to mix into the soil of our vegetable garden.  That was 11 years ago, and the (mostly) organic garden is now thriving, producing massive amounts of tomatoes, zucchini, green beans, and other vegetables each summer because of the myriad nutrients that animal manure adds to the soil.

Unfortunately, many home gardeners don’t have the good fortune to live next to a farm, so they can’t add local animal waste to their soil. And commercial farms, which produce the majority of food consumed in developed countries, preferentially utilize synthetic fertilizers over plant and animal waste.  However, many people disagree with the ubiquitous use of synthetic fertilizers in agriculture and instead advocate for natural fertilizers (animal and plant waste) instead.  But why should they care how soil is replenished?  Don’t both types of fertilizers provide the same nutrients for plants?

In short, no.  Scientists know that food crops require at least 14 mineral elements (and a few other trace elements) to grow healthy and to have large yields.  However, the major components of conventional fertilizers are just 3 of these elements– nitrogen, phosphorus, and potassium.  This situation is similar to eating only fats, carbohydrates, and proteins; neglecting all other nutrients (vitamins, minerals, antioxidants, etc.); and expecting to be healthy.  On the other hand, giving plants natural fertilizers provides a full buffet of nutrients in addition to the nitrogen, phosphorous, and potassium.

So why can commercial farms get away with providing such a limited diet for plants?  While nitrogen, phosphorous, and potassium are needed in large quantities and are depleted quickly, the other 11+ essential nutrients are needed only in trace amounts and can be obtained from the existing soil.  However, these nutrients are now dwindling from many years of farming the same land and only replenishing three nutrients.

Evidence already exists suggesting that nutrients in plants are decreasing with the rise in conventional farming techniques. A study conducted in 2004 compared the levels of nutrients in various food crops between 1950 and 1999, and they found that over time, levels of protein, calcium, phosphorous, iron, riboflavin, and ascorbic acid declined in 43 different fruits and vegetables.  Especially concerning is the decrease in iron levels, since more than 60% of the world’s population is already iron deficient. However, levels of another 7 nutrients did not change significantly, and the research group cautions people from drawing dramatic conclusions from these results alone, since there may be other explanations for the apparent decrease, such as the utilization of different plant cultivars and the trend towards selecting plants that produce higher yields at the expense of nutrient levels.

From this, one would think that the answer to the issue is to create a fertilizer that contains all of the essential nutrients.  But the answer is not so simple. Most plants cannot obtain sufficient levels of nutrients from the soil by themselves.  Instead, agricultural plants live in symbiosis with microbes that help plants manage their nutrients and make the nutrients more available.  However, conventional fertilizer is not just neglecting to replenish soil, it is also directly causing harm to the soil.  Adding high levels of nitrogen to the soil in the form of conventional fertilizer decreases the job of nitrogen-fixing bacteria in the soil and increases the activity of other soil inhabitants that consume nitrogen.  This increases soil decomposition, and ultimately make the soil less hospitable for crop plants. Even using plant breeding techniques and fertilizing plants with micronutrients does not guarantee that the nutrients will be available to the plant without the help of their symbiotic friends.

But how do these problems with soil actually impact our health? Excluding hydroponically grown food, all crop foods come from the soil, and these plants provide many essential nutrients for humans; if these essential nutrients are not present in plants because of poor soil, then humans will not access these essential nutrients.

If we cannot fix plants at the soil level, then perhaps we can fix them at the food level by adding the nutrients into processed foods (fortifying the food). However, the FDA does not currently allow fortification of fresh fruits and vegetables, and only processed foods would be affected. If we were to bandage the issue by fortifying foods, we would be enabling poor soil practices.  This is not to say that fortification of foods isn’t a good idea.  Fortification is helpful and often necessary to ensure that people, especially in developing countries, obtain the nutrients they need.  However, fortification is a problem when we use it as a crutch to remediate foods grown in poor soil.

There are many things we could change to create healthier soil.  For example, we could emphasize more crop rotations, encourage prolific use of organic animal and plant wastes as fertilizer, and support precision agriculture, where farmers and scientists use technology to apply fertilizers and irrigation selectively, depending upon existing nutrients in the soil.  We can also utilize biofortification, which uses conventional plant breeding techniques, genetic engineering, and other approaches to increase the total nutrients or nutrient bioavailability in food crops.  Biofortification can be more sustainable and less costly than the current method of food fortification after processing.

The point of this article is not to say that we should stop eating conventionally-grown fruits and vegetables because they might have fewer nutrients, or that we should stop growing foods conventionally using synthetic fertilizers and modern tilling and water practices.  The goal is to bring awareness to the idea that to preserve our health and that of future populations, we need to first and foremost care for our soil.  Without the healthy soil that nourishes the plants that sustain us, we will surely suffer.  As much as we may wish to deny it, our health is intimately tied to the health of the entire food system.  Even if the impacts of our current actions are not apparent now, the stress of an increasing global population and a decrease in health agricultural land may be felt soon in the future.