FEEDING THE TEN BILLION
PLANTS AND POPULATION GROWTH
L.T. EVANS
CAMBRIDGE UNIVERSITY PRESS 1998
PART XIV
Chapter 12: Feeding the Ten Billion (Cont.)
12.5 Old and new crops
We are an exploratory, inventive species, fascinated by the new, dispensing with the old. So ‘new’ crops attract optimistic headlines while old ones are often blamed for the problems of agriculture. Yet the world still relies on three of the oldest domesticates – one from the Near East, one from Asia and one from the Americas – for the bulk of its food and feed supply.
More than 2,000 plant species have been domesticated to some extent over the last 10,000 years. Many of these are still cultivated on a small scale, often quite locally, like teff in Ethiopia. Others have either been replaced or displaced to poorer conditions by crops which are more productive, reliable, adaptable or nutritious, and the most important of these have become the staple crops which provide most of the world’s food.
Since the introduction of cheaper nitrogenous fertilizers the cereals have extended their dominance of our food supply, at the expense of legumes and root crops. Likewise, wheat, rice and maize have become progressively more predominant among cereals, their share of world cereal production having increased from 69% in 1950 to 84% today. They dominate the diets of many developing countries and the food supplies of developed ones. But dependence and blame are frequent fellow travelers, and intensive cropping is often faulted for being less sustainable and more environmentally harmful than, for example, legume cropping.
New crops have been promoted on the grounds that there is insufficient genetic diversity in the old ones, despite the comprehensive gene bank collections of wild relatives, land races and varieties of the major crops, e.g. of more than 80,000 accessions for rice. Modern varieties of staples are also claimed to have narrow genetic backgrounds and therefore to be vulnerable to pests and diseases. But with almost 70 land races, from many regions, in the ancestry of recent CIMMYT wheat varieties and a comparable diversity in dwarf rice and hybrid maize ancestries, their genetic background has never been so wide. Any variety outstanding enough to be grown on 10 M ha must have a comprehensive set of genetic resistances and will have those exposed to extensive challenge by pests and diseases. Narrow ecological adaptation is another brickbat thrown at the staple crops, yet one of their outstanding features and a key to their success has been their adaptability. Nor do they ‘need’ high inputs, as is often claimed. Rather, they respond well to them.
- So-called new crops fall into several categories. Most are old crops in the sense of having been domesticated long ago, often cherished for the variety they added to diets and farming systems but gradually displaced by more reliable crops, religious decree, and by mechanization. There are many books on these, such as The Lost Crops of the Incas (1989).
- A second category of ‘new’ crops consists of old ones put to new uses, as when fodder beet (chard) was selected as a source of sugar in Napoleonic times.
- Other examples could be given and many more are in the pipeline for the future, based on genetic engineering to enhance or inhibit specific constituents for nutritional or industrial purposes.
In the truly new crop category the species range through oil crops such as jojoba and Melaleuca, still not domesticated; American wild rice (Zizania), still in the throes of being domesticated; several recently domesticated lupin species now used as feed grains; and triticale, on the way to becoming an important crop which could challenge wheat on sandy or acid soils, and in cold climates, as feed and, if its protein composition can be modified, even for bread making. There are also many suggestions for new crops based on slender ecological observations.
- It seems unlikely that ‘new’ crops will reduce our dependence on rising yields of the old staple crops to match food supply with population growth.
- Whether the ‘new’ crops are ‘lost’, genetically engineered or newly domesticated, they can play a valuable role in the diversification of both our diets and agriculture.
- The role of the staple cereals in feeding the world might then become less crucial.
12.7 Global climate change and food supply
This is not the first time that agriculture has encountered a period of climate change. Indeed, V. Gordon Childe, who fathered the concept of a Neolithic Revolution, believed it was climatic change which led mankind to the agricultural way of life. Rowan Sage has suggested that it was not until the rise in atmospheric CO2 level between 15,000 and 12,000 years ago that cropping could have been sufficiently productive to make agriculture worthwhile. Since then the decline of Sumerian irrigation (over 4,000 years ago), the desertification of the Negev and the erosion of the Aegean hills over 2,000 years ago, the migration of Arabs to the Near East about 700 AD, the decline of the Maya about 800 AD and ‘the little Ice Age’ from 1550 to 1850 have all been associated with periods of changing climate. But with the human population currently ten times greater than it was in AD 1600, the stakes are now higher.
- The most important element of current change is the rise in the atmospheric concentration of several ‘greenhouse’ (i.e. heat-trapping) gases such as carbon dioxide as a result of industrial, agricultural and other human activities.
- When the heat trapping effect of all the gases is converted to CO2 equivalents, the doubling of its concentration (i.e. reaching 600 parts per million) is expected to occur by the year 2060.
- As greenhouse gases increase, so also will the average global temperature, with estimates varying between 1.5 and 4.5°C.
- Seasonal rainfall patterns are also likely to be affected, to uncertain extents.
- At high latitudes, warmer conditions may be agriculturally advantageous, allowing new arable land to be brought into production and extending the season for crop growth.
- At low latitudes, crop duration and yield will be reduced but opportunities for intensification increased.
- With the rise in temperature there will also be a rise in sea level and some loss of arable land, e.g. in Bangladesh.
- The rise in temperature will reduce the water use efficiency of crops, but that effect may be counterbalanced by the rise in CO2, which tends to reduce the density and opening of the stomatal pores in leaves.
- The net effect of these responses will vary from crop to crop and with the extent of cloud cover, one of the least predictable of the effects of global warming, along with changes in rainfall patterns.
- For many crops, particularly under high light conditions, a rise in CO2 initially results in faster photosynthesis, growth and yield.
- Only bold spirits would try to project, on a world scale, the effects of climate change on food production when there are ten billion of us.
- It is likely that the adverse effect of climate change will fall most heavily on the developing countries at low latitudes, particularly in West Asia, sub-Saharan Africa and Central America, implying a greater dependence on international trade for their staple foods.
It appears, therefore, that both plant breeders and agronomists will be stretched over the next decades not only to raise yields to keep pace with population growth and urban appropriation of the best arable land, but also to adapt the major crops and their agronomy to warmer climates, and possibly even more so to any abrupt change to the distinctly cold conditions which they could precipitate within a century, possibly accompanied by much drier tropics.
12.8 What chance a brown revolution?