Cicer arietinum – “strong ramshead” – leads a life of the most exquisite harmony with a species of remarkable bacteria in the earth. In the first week after sowing, the chickpea thrusts down an intrepid taproot – a combined anchor, food store and sophisticated search and absorption system for water and other vital nutrients. Then, a day or so later, tiny spheres start to become visible on the developing root system. Two weeks into the young plant’s life and the spheres become nodules, up to 3 centimetres long, whose delicate pink coloration is due to the same pigment which stains our own blood red. These nodules are not, however, an intrinsic part of the chickpea; they are symptoms – early evidence that the plant has sustained an infection.
Contagious though it is, this disease is far from being pestilential. The root cause, so to speak, is a truly benevolent bacterium, Rhizobium, and we are all its beneficiaries.
The strain of Rhizobium which infects (”graces” would be a more decorous word to use) the chickpea will not live with any other plant; it is utterly faithful to its host. In return for this devotion, the chickpea affords the Rhizobium food and shelter in its multiplying root system. Then, in the mouldy darkness, the Rhizobium starts to work its earth magic. Pulling nitrogen out of thin air (three quarters of our atmosphere consists of nitrogen gas) the Rhizobium chemically binds it with hydrogen to produce ammonia. This, in itself, is an impressive feat of bio-chemical engineering; for atmospheric nitrogen is a pretty unreactive substance not easily entrapped. From ammonia, plants can produce amino (”derived from ammonia”) acids and from amino acids, they produce protein. How much? Well, the chickpea contains nearly three times as much protein as an equivalent weight of whole milk. For which magnificent achievement, the unseen Rhizobium must take credit.
The benefits of this symbiotic harmony between plant and microbe go deeper still. As any farmer knows, repeated crop sowings will, sooner or later, deplete his field of essential nutrients, especially nitrogen. Hence the world’s gluttonous appetite for man-made nitrogen fertilisers, 160 million tonnes every year, at a price of $10,000 million. The real cost, in fact, is far higher still; add in the water pollution caused by fertilizer run-off, the soil degradation, the diminishing returns of chemically-addicted agriculture, and the price tag quickly becomes ruinous.
There is a saner way to keep our crop yields up without depleting every resource in sight; Rhizobium’s way. Every year, these humble bacteria and their cousins quietly add 35 million tonnes of natural nitrogen to the world’s soil. And the farmer who grows chickpeas (complete with their dedicated Rhizobium) benefits twice-once from the naturally-fertilized chickpea harvest, and again when the field is used for subsequent crops. Scientists have demonstrated that chickpeas can “fix” 250 kilograms or more of nitrogen per hectare, which is about the equivalent of two and a half tonnes of artificial fertilizer. Or, put another way, growing chickpeas in your field naturally increases the yield of subsequent crops such as maize or wheat by the same amount as if the field had been lying fallow and unproductive. Quite some team, the redoubtable Rhizobium and the rugged ramshead.
