Crop Comments: Harnessing buckwheat’s ability to liberate phosphorus

My favorite local honey is buckwheat-based. Honey consumers typically believe that the human health benefits of this food are greater if the beehives are situated near where that consumer lives. Bears appear to share this mindset.

Honeybees are critical for the pollination of this plant species, which provides high quality pollen for these industrious six-leggers. (Experts refer to this relationship between plants and animals as symbiosis.)

Buckwheat (scientific name Fagospyrum esculentum) is a moisture-loving cool climate summer annual, with many potential uses in sustainable cropping systems. Grown in China as a grain crop for over 1,000 years, buckwheat is one of the quickest-growing green manure crops. It takes only four to six weeks from seeding to flowering, and another four to five weeks until seed maturity. Used to suppress weeds, it protects the soil from erosion, attracting beneficial insects (including honeybees) and builds soil organic matter.

Buckwheat repels weeds through a trait called allelopathy. It secretes a chemical (in effect a natural herbicide) which seriously discourages many other plant species. Although modern herbicides have greatly reduced the need for so-called smother crops, buckwheat may still be useful for this purpose due to its allelopathic properties. Also, F. esculentum is a good competitor because it germinates rapidly, plus its dense canopy shades the soil, with rapid growth quickly choking out most weeds.

According to 1989 research at University of Wisconsin-Madison (by Oplinger and Oelke), buckwheat’s dense canopy soon shades soil, stealing solar radiation from less aggressive plant species. Not surprisingly, it is useful for controlling quackgrass in the Northeast. Even though rapid and complete control should not be expected, a heavy buckwheat stand should smother most quackgrass, if the land has been thoroughly tilled to break up this weed’s sod. Then such fields should be autumn-plowed, or early spring-plowed, then disked or field cultivated just prior to planting time.

Weed scientists report that buckwheat can be used to eradicate Canada thistle, sow thistle, creeping jenny, leafy spurge, Russian knapweed and perennial peppergrass, just to name a few.

Very importantly, in the face of the ongoing global fertilizer economics mess, buckwheat can also increase phosphorus’ and micronutrients’ availability for the next crop in the rotation. It performs this service by liberating complexed soil nutrients through acidulation. With this trait, the plant’s root tips secrete acids (typically malic and citric), which chemically separate phosphorus and trace elements from soil particles. These, in turn, nourish the buckwheat, generally with enough left over, to feed the next crop in the rotation. However, F. esculentum doesn’t fix nitrogen.

Mature seed averages about the same amount of protein (12% – 13%) as most other small grains. Buckwheat is a broadleaf annual crop, normally reaching two to three feet height, with a single succulent stem possessing several branches. Its flowers vary from white or light green to pink or even red. Forming a dense, fibrous root system with a deep taproot, most of its roots are concentrated in the top ten inches of soil. Its total biomass ranges between 2,000 and 3,000 lbs./acre.

In addition to being very attractive to honeybees, this crop also attracts wasps and parasitic flies. But it also has two major shortcomings: its intolerance to frost and its susceptibility to herbicide residues. This herbicide intolerance is the main reason why buckwheat acreage in the U.S. dropped significantly since World War II. At that milestone, many of the chemicals used to make wartime munitions were diverted to ag chemical production. Early in the 20th century, approximately one million acres were planted to this crop. By the 1960s, that figure had plummeted to 60,000, roughly its present acreage.

Buckwheat can sensibly be planted up till July 15, particularly on land which has been unproductive, often overtaken by goldenrod and/or burdocks. Prepare a good seedbed, but don’t pulverize it. Plant like other small grains, drilled or spun on, but only 50 lbs./acre (unlike other small grains, seeded at much higher rates). Drag in lightly if spun on. This crop tolerates pH of 5.0 – 6.0, as well as generally low fertility, making it a great way to bring back abandoned land.

Considering its human health benefits, University of Illinois scientists have determined that dark-colored honey, specifically the kind produced with nectar from buckwheat blossoms, contains 20 times the amounts of antioxidants found in paler honey varieties. Quoting those researchers, “Antioxidants are the body’s first defense against free radicals that produce inflammation and tissue damage. Although increasing antioxidant levels won’t reverse damage done by free radicals, it can prevent further cell deterioration. Buckwheat honey packs the antioxidant of the vitamin C in a tomato.”

According to ancient Greek philosopher Aristotle, “The best fertilizer on the land is the footsteps of the owner.” When I walk through a buckwheat stand, listening to buzzing honeybees, the ground actually feels softer under my feet: the buckwheat has, in fact, mellowed the soil.

All that philosophy aside, I just like how buckwheat honey tastes on an English muffin – or better yet, buckwheat pancakes. This last combination boasts a flavor that’s burly, a trait not unlike the plant that donated the raw material nectar to the hard-working bees.

A few growing seasons ago, I got a local organic farmer to plant a unique seed blend – a creation of mine (and some other deep-thinking agronomists). This seed concoction contained, drilled per acre, 5 lbs. of tillage radish seed, 25 lbs. of buckwheat seed and a bushel of oat seed. Here’s how that crop performed: The buckwheat died with the first killing frost. (It was then immediately round-baled.) But by that time, it had achieved its acidulation and allelopathy missions. The radishes did their soil penetration thing, accompanied by the oats. When it got really cold, the radishes and oats called it quits, but all three crops did a great job of maintaining ground cover, ultimately to quietly self-compost under the snow.

Here’s another take-home message: With the phosphorus fertilizer economics so tied up with Middle East geopolitics, buckwheat’s ability to liberate that nutrient through acidulation certainly continues to merit the attention of crop growers.

by Paris Reidhead