Despite many historians believing that clovers have truly changed the world, these crops are surprisingly modest creeping herbs, rarely reaching knee-height.
According to my textbook “Around the World in 80 Plants” (Jonathan Drori, Lawrence King Publishing), there are two common cultivated species, both with plump, sweet-scented flowers about the size of a cherry. There are red clovers (Trifolium pretense, boasting magenta pigment), adapted to pollination by long-tongued bumblebees. There are white clovers (T. repense), which attract shorter-tongued honeybees.
The most impressive clover fields sprawl across the flat, fertile countryside of Denmark, a nation exporting huge tonnages of these legume seeds. In Ireland, we find yellow clover (T. dubium), the species considered by most Irish to produce the true shamrock.
Plants photosynthesize by using carbon dioxide absorbed through their leaves, and water through their roots, but they need other nutrients from the soil, especially nitrogen (N) compounds and phosphorus (P). When crops are taken from the soil, those nutrients are removed. If those nutrients aren’t replaced – in the form, for example, of animal manure – crop yields suffer. The usual way to counter likely yield loss is by applying N compounds and other nutrients.
Certain plants help defray expenses associated with these usually purchased plant feedstuffs. These are the legumes, plant families that include clovers, peas, beans, lentils, alfalfa and even trees like locust and mesquite. Legumes tap into the abundant N in the atmosphere, employing fancy chemistry to convert N into nourishment for themselves and other plants.
All legumes enjoy a relationship with special bacteria, ones belonging to the Rhizobium genus and living on these plants’ roots. Such bacteria take N from air and “fix” it, creating amino acids which are then crafted through biochemistry into proteins. These proteins can become part of our diets or are fed to animals that feed us with their milk or meat. Over many centuries, farmers have incorporated legumes into crop programs because of this N-fixing trait.
Drori pointed out that clovers are very good at fixing N out of air and accumulating P. Clovers were first domesticated in the Arabic part of Spain during the 10th century but weren’t planted widely in Europe until the 1600s. At that time, European agriculture (including the soils supporting it) was suffering an N deficit caused by exporting cereal grains to the growing cities. Human wastes from those cities weren’t handily returned to farm soils, so directly, or indirectly, clover became essential for feeding those populations.
During the 1700s and 1800s, according to Drori, “agricultural production [in Europe] skyrocketed. Clover meant fatter cattle, more milk and meat and better crops. With all the extra food, the European population almost tripled in that period.”
Healthy existence of clover species was facilitated by sweetness during that era of agricultural growth: clover flowers needed to be pollinated, so bees had a field day and honey production soared. The clover landscape, an artistic patchwork of red, white and green fields, became part of Europe’s identity. In modern European languages are commonplace sayings such as the English phrase “being in clover,” implying an easy or settled life.
Once three-leaf clovers became associated with good luck, the common mindset was that the mutant four-leaf kind could only be luckier. Naturally occurring only once in several thousand stems, they are rare enough to be special. Whether any firm relationship exists between four-leaf clovers and successfully placing bets in gambling establishments is up for debate.
In order to create agricultural N faster than legumes, in 1909 German chemist Fritz Haber invented a method for synthesizing N compounds as fertilizer ingredients. This achievement earned him a Nobel Prize that year, for his skill in converting methane (natural gas) and air (which is 78% N) to plant food called urea. Haber’s process was globally scaled up after World War II, sadly relegating the non-synthetic clover-Rhizobium “partnership” to second fiddle status.
The rapid growth of synthetic fertilizers spawned by Haber has allowed crop yields, and thus world population, to increase, but, according to Drori, “it uses prodigious amounts of energy, greatly exacerbating climate change. Runoff into rivers and oceans creates dead zones from algal blooms and the landscape has become dominated by artificially fertilized monocultures, with their increased dependence on herbicides and pesticides, losing biodiversity as well as charm.”
Drori closed, “Meanwhile, agriculture combining traditional crop rotation and clover varieties is increasingly competitive. Enlightened farmers are reintroducing clover to the countryside, and with it the bees and other pollinators that are so important for biodiversity.”
Another clover – special to me – is crimson clover (T. incarnatum), which is grown as a winter annual primarily in the Southeast, the Pacific Northwest and California. It thrives in cool, humid conditions, not tolerating drought or extreme heat or cold. I studied crimson clover in a basic field crops course at Cornell in the mid-1960s. Upon starting grad school at Louisiana State University, I saw this legume growing prolifically in that region. When I enrolled at LSU in 1968, a popular song came out titled “Crimson and Clover” by Tommy James and the Shondells. (It was a love song, not about legumes.)
During my drives from New York, that song was frequently played on my car’s radio. That song accompanied me as my Dodge Coronet’s lonely headlights lasered through the Piedmont blackness. To this day, I can’t hear that James classic without thinking about actual crimson clover.
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