Soil Part I: Seaweed Fertilizer
“The nation that destroys its soil destroys itself.” President Franklin D. Roosevelt
I am frequently drawn to write columns about soil, due to its vital importance as a national resource as well as the fact that we treat it so poorly. In this column, I will weave together some of the points I have made in the past and also explain why we should consider using seaweed-based fertilizers.
First, let’s talk about soil. An ideal soil has approximately 50% of its volume filled with solids and the other 50% with water and air. Ninety percent of the solids should be minerals, basically eroded rocks, and 10% should be organic matter such as decaying leaves. The spaces between the solids accommodate water and allow air to reach plant roots, a vital step in plant growth. Healthy soil is the most biologically productive environment on Earth. A single gram of soil can contain up to a billion organisms, representing over a thousand species.
Soil contains approximately 70 different minerals. Thirteen of these are known to be essential for plant growth: nitrogen, phosphorous, potassium, sulfur, calcium, magnesium, iron, boron, manganese, copper, zinc, molybdenum, and chlorine. The other 50 or so, including things like cobalt, iodine and selenium, often referred to as micronutrients, are likely to be important to plant growth even if the mechanisms are not fully understood. For plants to be able to utilize these minerals efficiently, the soil environment must have proper moisture, pH, and organic content. In particular, when soils become deficient in organic matter, the ability of plants to absorb minerals from the soil drops precipitously.
In a similar fashion to plants, humans need a wide array of minerals in our diet to maintain our health. With the exception of taking vitamin supplements, a practice which is less effective than you might think, we get the vast majority of our minerals from the soil, either by eating plants(1) that have extracted them from the soil for us, or by eating animals that have eaten plants. Seafood provides another important source of minerals. As you might guess based on the title of this column, you will read more on that subject below.
As farmers harvest plants, minerals which had formerly been in the soil are removed. Unless these minerals are replaced, the field will quickly lose productivity. Replenishment of minerals can be accomplished by the application of fertilizer or by extraction from rocks already in the soil through the action of fungi and/or ground water. Nitrogen is a special case, in that it can be extracted from the air through cooperative action of a legume such as alfalfa and several types of micro-organisms in the soil. For more on this topic, I recommend my previous column Fun with Fritz and Carl.
Generally speaking, the industrial agriculture systems in the United States are not particularly effective at replacing soil minerals. Most fertilizers applied on large U.S. agricultural operations include only nitrogen, phosphorous, potassium and, at best, a small handful of other minerals. To make matters worse, over-tilling and insufficient application of compost result in a reduction of the soil’s organic content. Therefore, the absorption of even the small subset of minerals applied to the fields is inefficient. To overcome this inefficiency, farmers increase the amount of fertilizer that they apply, which then results in the run-off of excess nitrogen and phosphorous into the surrounding watershed, which creates a number of additional problems.
You may be asking yourself, “If the situation is as bleak as what Jeff is describing, how is it that we keep growing billions of pounds of corn, wheat, and lettuce every year?” The answer is that a large ear of corn and a nutrient-filled ear of corn are not the same thing. Just as one can raise a full-sized but unhealthy child on a diet consisting primarily of Twinkies® and Fruit Loops®, you can also grow a field of unhealthful corn, devoid of many minerals and nutrients, by limiting fertilization to just nitrogen, phosphorous and potassium, the Twinkies® of plant growth.
The United States Department of Agriculture has been tracking the impact of the depletion of our soils since the 1950s. Every year, they analyze the vitamin and mineral contents of approximately forty common foods, including carrots, apples, wheat, and chicken. As the decades have passed, the vitamin and mineral content of these foods has dropped in the range of 10-30%. This slow erosion of food quality in the U.S. is a key, but little discussed, underlying cause of many of our public health challenges.
So what can we do to reverse this trend? We can improve our soil management practices (which I will address next week in Part II) and we can use fertilizers which contain a broader array of minerals by looking to the oceans.
Since the oceans of the world are downstream from everywhere, they are not depleted of minerals. The cobalt, iron, and selenium content of the oceans are roughly the same as they were when our ancestors first crawled up on the sand. Therefore, plants which live in the ocean can, and do, absorb up to 50 to 60 different minerals, including the full array of micronutrients.(2) This characteristic is key to the attractiveness of seaweed both as a fertilizer and a health food. Japan utilizes seaweed extensively in both of these capacities.
Given our long coastline with its variety of inlets and bays, North Carolina has the potential to develop a successful seaweed farming industry. To me, there is a certain beauty in the idea. Minerals from our fields find their way from the soil, to our food, to us, and then to the ocean (I’ll let you puzzle out the mechanisms and pathways on your own). Then the seaweed can collect these minerals for us so that we can harvest them and bring those minerals back to our fields. There may be efforts to develop seaweed farming in NC already occurring. If any readers are aware of them, please let me know.
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(1) For simplicity, I am including mushrooms, which are fungi, as plants.
(2) For the purposes of this column, I am ignoring the effects of ocean acidification due to the increased concentration of carbon dioxide in the atmosphere. When the concentration of carbon dioxide in the atmosphere rises, more of it becomes dissolved in the oceans. Dissolved carbon dioxide forms carbonic acid and reduces the pH of the water. Just as I discussed above regarding soil pH, changes in the pH of the ocean affect the ability of plants in the ocean to absorb minerals. The ongoing acidification of the oceans is predicted to decrease the ability of plants to absorb minerals and, thereby, have a strong detrimental effect on biological productivity. But the mineral depletion our soils are experiencing is more immediate, and therefore the focus of this column.