Think of all the energy expended in planting fresh cereal grain every year to ensure just one season’s crop. Then think of all the energy expended in repeating the process each year. What savings there would be if these crop plants could be sown once and their food parts harvested repeatedly. Science fiction? Fanciful wishful thinking? Maybe, but quite why there are no perennial grain crops is a bit of a puzzle and is pondered by David Van Tassel and colleagues (Evolutionary Applications; doi:10.1111/j.1752-4571.2010.00132.x).
They conclude that perennial grain crops do not exist today because they could not have evolved under the original set of conditions (the selection pressures imposed upon plants by Man on the cusp of developing agriculture). However, they contend that they can be developed today through artificial phenotypic and genotypic selection. Coincidentally, a ‘Policy Forum’ item in Science magazine also addresses this very topic (though it’s probably not a coincidence since three of its 29 signatories are the authors of the Evol. Appl. paper).
Jerry Glover et al. (Science 328: 1638–1639, 2010) argue that our current global agricultural regime – which is heavily biased towards annual grain production – often compromises essential ecosystem services, pushing some beyond sustainable boundaries. To ensure future food and ecosystem security, farmers need more options to produce grains under different, generally less-favourable circumstances than those under which increases in food security were achieved this past century. Development of… perennial versions of important grain crops could expand options.
And not to be outdone by the journal ‘across the pond’, the London-based science journal Nature also has its own editorial on feeding a hungry world. Intriguingly, this latter item, whilst calling for a second green revolution, does not seem to mention perenniality; evidence for a trans-Atlantic divergence on this possibility?
Yes, that is an intriguing possibility. Would like to see a face-to-face debate on that. Incidentally, we wrote about the van Tassel paper here: http://agro.biodiver.se/2010/06/the-road-to-perennial-cereals/.
Sorry about the delay in getting the comment up. For some reason Akismet is being a bit over-zealous today.
Crop rotation was an important innovation in agriculture; it would not be possible in a perennial grain crop. While weed control may not be a problem because of good establishment of the crop, both nutrient depletion and particularly disease build up (fungal, viral, nematode and insect) might be insurmountable in any herbaceous crop. Isn’t a first step towards a perennial cereal having a system where it can be replanted year-after-year and still give economic yields? Disease build-up is not mentioned as one of the hypotheses by van Tassel et al., but seems to me a critical disadvantage for perennial cereals, and indeed most other herbaceous annual crops.
Disease build-up (especially viruses) is indeed a problem in crops like sweet potato. The experience of agroforestry would seem to suggest that agricultural systems based on some combination of perennial crops may indeed be possible.