New crops: perennial grains?
Most of our staple crops are annuals—plants that grow from seed, produce the next generation of seeds and then die, all in one year. In particular, the ‘big three’ crops, rice, wheat and maize, are all annuals. What would life be like if we instead grew perennials—plants that last more than one year? No more yearly ploughing and sowing.
First things first: we’ve already got plenty of perennial crops. Many fruits, such as apples, grapes and kiwis, grow on trees and vines, and plants like the tomato can grow as annuals or perennials. But they’re luxuries, not our daily bread. The cereals and pulses that we depend on are almost all annuals.
There’s probably a reason for that. One might be that, because annual plants have evolved to die after producing their seeds, they pour all of their energy into seeds, which are what we harvest. Another part of the equation is that ploughing the soil is a simple and effective way to kill weeds which might compete with the crop.
To keep it in perspective, though, the idea isn’t to replace the crops we’ve spent 10,000 years breeding. Rather, perennial crops may be able to produce food in harsh environments where conventional crops fare poorly—which could well be the parts of the world where they’re most needed. With larger root systems, they can use water and nutrients more efficiently, and by leaving less bare soil, they reduce water lost by evaporation from the soil surface.
There are also environmental benefits. Farmers growing perennial crops might allow more biodiversity to remain among them (think of the difference between an orchard and a wheat field), although that might be wishful thinking. The soil, left unploughed, will probably accumulate more carbon, while soil erosion and fertiliser running into rivers will be reduced.
Is it realistic? At a glance, yes: both rice and maize have close relatives (in the same genus) which are perennial, while wheat’s closest perennial relative, Thinopyrum, is a bit more distant. Nothing but a spot of cross breeding to do? Well, apparently both the US and the Soviet Union had a shot at it (with wheat) back in the 60s, and didn’t get very far. Perhaps the technology we’ve developed in the last 50 years—to read and understand genes, and then to alter them—can accelerate the process. Or maybe, taking a broader view of world crops, we’ll find a better starting point than wheat.
I’ll leave you with some numbers: the yield per hectare of four major annual crops and a selection of perennials. Some of the perennials do very respectably, although yield’s not everything.
|Almonds, with shell||1131|
|Cashew nuts, with shell||908|
|Hazelnuts, with shell||1241|
|Oil palm fruit*||14080|
|Walnuts, with shell||2400|
* According to Wikipedia, this yields some 22% oil, giving about 3100 kg per hectare. (Data from FAOSTAT, for 2008)
Glover, J., Reganold, J., Bell, L., Borevitz, J., Brummer, E., Buckler, E., Cox, C., Cox, T., Crews, T., Culman, S., DeHaan, L., Eriksson, D., Gill, B., Holland, J., Hu, F., Hulke, B., Ibrahim, A., Jackson, W., Jones, S., Murray, S., Paterson, A., Ploschuk, E., Sacks, E., Snapp, S., Tao, D., Van Tassel, D., Wade, L., Wyse, D., & Xu, Y. (2010). Increased Food and Ecosystem Security via Perennial Grains Science, 328 (5986), 1638-1639 DOI: 10.1126/science.1188761