Part 1 | What makes a Healthy Diet — for People, Plants and Soil? (2024)

Part 1 of a two parter by Stephanie Reiter (Global Soil Partnership Secretaria) and Lucrezia Caon (UN Food and Agriculture Organization). This part introduces soil, and a soil ‘diet plan’ while part two focuses on how to be a soil doctor.

Just as we feel better when we eat a healthy diet, plants grow better on soils that provide them with a healthy diet. No matter which diet we choose for ourselves, our bodies and minds are fueled by what we eat, and food production is powered by its soils’ diet. We need to know what makes a healthy soil diet. To start, there is an unquestionable link between the nutritional value of the food we consume and the health of the soil on which it grows. Globally, about 95% of our food is directly or indirectly produced on soils.

There are 17 of what are called Global Goals, or Sustainable Development Goals (SDGs). These have been developed by the United Nations to help improve socio-economic and environmental conditions in the world. If we want to achieve Sustainable Development Goal 2 –Zero Hunger — “End hunger, achieve food security and improved nutrition and promote sustainable agriculture”, if we want in fact to improve human nutrition and work towards ending malnutrition, we need to make sure that our soils are healthy too.

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Healthy soils supply water, oxygen, and all essential nutrients that crops need to grow and flourish. The core of a healthy soil diet are relatively large amounts of the primary macronutrients nitrogen, phosphorus and potassium. These three main ingredients are vital to plants and required in large amounts to ensure plants grow, flower and produce. Nitrogen plays a central role in plant metabolism as a constituent of proteins, nucleic acids, and is a critical component of chlorophyll, which is essential for photosynthesis. As a structural element of nucleic acids and a component of adenosine phosphates, phosphorus is important for energy transfers, and helps to move sugars from leaves where they are produced to fruits and seeds. Potassium is mainly important for cell extension and stomatal opening and closing, it also supports disease resistance and water-use efficiency within plants.

Optimally, a healthy soil diet is supplemented by the three intermediate nutrients sulfur, calcium and magnesium required in medium quantities, and the nine micronutrients boron, chlorine, copper, iron, manganese, molybdenum, nickel, sodium, and zinc, required in minute amounts. These ingredients are not just a dietary fad but are critical for plants to function and develop. Micronutrient deficiency in soils can lead to human micronutrient malnutrition, and a shortage of any of the fifteen named nutrients can limit plant growth, lower yields, and decrease the nutritional value of our food

Doctors recommend low sodium consumption and a reduction of salt amounts in our diet. Most people consume too much salt, even though high sodium consumption can increase the risk of cardiovascular diseases. Cutting salt from the human diet plan is beneficial to our health, and again, the same applies to our soils. Their state of health is more and more threatened by the increasing salt concentrations found in soils worldwide. Salinization means the accumulation of water-soluble salts from sodium, magnesium and calcium in the soil that can happen naturally but is exacerbated through the use of mineral fertilizers for agriculture. Plant growth is highly limited on saline soils and in extreme cases salinization can result in a complete collapse of the soil system destroying plants and other living organisms, ruining the possibility of growing crops there.

Our ideal body pH is about 7.4, slightly alkaline. There are several alkalizing or neutral foods such as potatoes, lentils and most green vegetables that can reduce the negative health effects caused by a high body acidity. Just as an overconsumption of high-acid foods like sugars in our diet can be harmful to our health, high nitrogen and sulfur use in fields, deteriorates soil health. A soil diet with lots of acidifying ingredients, including fertilizers like these, lowers the soil pH away from the optimum for plant growth: for most crops this is between pH 6.0 and 8.2. Low pH makes toxic aluminum soluble and makes other the major soil nutrients important for plant growth unavailable for root uptake.

We can think of our own diet and apply the same principles when setting up a plant and soil diet plan. We prefer a balanced diet, not at least to enjoy all kinds of flavors and taste adventures, but to get an intake of the full range of nutrients. The soil needs variety too.

Unfortunately, many of our soils have been on a rather bad diet since the massive intensification of agriculture in the 1930’s, called the Green Revolution. Increasingly, soils are getting crammed with junk-food like chemical fertilizers, threatening their total collapse. The trend of deteriorating soils globally is in urgent need of a solution because it is accelerated by global population growth, urban expansion, land use changes, and exacerbated by climate change and rapid human dietary shifts. Our diet is increasingly seen as central to environmental issues like soil degradation: what we put on our plates now determines our world’s future.

To put it bluntly, if we follow current human dietary patterns and stick to unsustainable agricultural practices that harm our food producing soils, we won’t have to argue anymore if the best, healthiest diet is paleo, vegetarian or strictly plant-based because our plates will be empty.

Stephanie is a Geoecologist, holding a M.Sc. degree from the University Potsdam, Germany. She is passionate about soils and curious to investigate the various interconnections within our environment. As a consultant for the Global Soil Partnership of the Food and Agriculture Organization of the United Nations she evaluates the GROW Soil Nutrient Testing Kit to provide Growers with a reliable tool to equip them to manage their soils in a sustainable and healthy way.