Will yield increases continue to feed the world? The case for wheat
by Tony Fischer / September 25, 2014
Tony Fisher is Plant Industry Honorary Fellow with the Commonwealth Scientific and Industrial Research Organization (CSIRO). Any opinions expressed are his own
The release of the bread wheat variety Borlaug100 earlier this year in the irrigated Yaqui Valley of northwest Mexico was both apt and reassuring.
The 100th anniversary of the late scientist Norman Borlaug’s birth was also celebrated in 2014. The performance of his namesake wheat variety represented a notable jump in potential yield, lifting bread wheat up to the potential of the best durum wheat variety, currently dominant in the valley.
Borlaug, who is credited with saving more than 1 billion lives, was awarded the Nobel Peace Prize in 1970 for his work at the International Maize and Wheat Improvement Center (CIMMYT) and its predecessor organization, the Office of Special Studies, where he began breeding wheat in the 1940s. Scientist Sanjaya Rajaram took over leadership of breeding in 1972, followed by Maarten van Ginkel in 1995, and Ravi Singh as breeder for irrigated areas in 2005. Between 1950 and 2014, potential yield of the approximately 160,000 hectares (400,000 acres) of wheat in the valley increased from about 5 metric tons (5.5 tons) per hectare to 9 metric tons per hectare, while farm yield rose five-fold, from 1.3 metric tons per hectare to 6.5 metric tons per hectare as varieties and agronomic management improved hand in hand.
These technologies have also had an impact on many developing countries with similar or related wheat agro-ecologies.
Many people are quick to point out that yield is not everything in global food security, that other issues are also important, including grain nutritive value, yield stability in the face of pests and diseases, crop input requirements, and more broadly, access of the poor to food (income and price), diversion of grain to animal feed and biofuel, and losses due to wastage.
However, nutritive value of the staples has not greatly changed, nor have yields become less stable, while input use per kilogram of grain produced has decreased, so that none of those issues are as fundamental to food security as farm yield increase.
Indeed yield increase has contributed more than 80 percent of the huge global consumption increase over the last 50 years (incidentally supplying of the burgeoning world population with more calories per capita). The increase in arable land area contributed only about half of the remaining supply increase, since cropping intensity (crops per year per hectare of arable land) also increased. This yield increase has saved vast areas of land from the plow. It is for these reasons that the subtitle of my recent book, Crop yields and global food security: will yield increase continue to feed the world?, asks whether yield increase will continue to feed the world.
While the book looked at past and prospective farm yield change across many crops, here space permits only a brief look at the global wheat yield situation.
The importance of wheat as a food calorie and protein source has already been pointed out in this “Wheat Matters” series of blogs: suffice to say wheat, being produced equally in developing and developed countries, is the top global source of calories (rice is actually the top source for poor consumers) and the top traded food grain, a position it is unlikely to lose.
Estimates of wheat-demand increase from 2010 to 2050 vary considerably: if prices are to be kept no greater than 2010 average real prices, I estimate a supply increase of about 50 percent is needed. Thus production needs to grow at 1.25 percent a year linear relative to the 2010 yield in order to meet estimated demand growth, but currently world wheat yield is growing at only 1 percent a year (relative to the 2010 trend yield of 3.0 metric tons per hectare).
While the potential yield of wheat has been lifted remarkably by breeding, as was seen in the example above, current rates of potential yield progress have slowed, averaging only 0.6 percent a year (range 0.3 to 1.1 percent) across 12 case studies around the world.
Experience suggests that the newest varieties are adopted relatively quickly by farmers and should as a consequence lift farm yield by about the same relative amount (i.e. 0.6 percent a year).
A separate source of progress in farm yield comes from farmers adopting new management practices, which close the gap between farm and potential yield. Actually, the current gap averaged only 48 percent (of farm yield itself), ranging from 23 percent to 69 percent across the case studies, with little difference between developing and developed countries, or irrigated and rainfed environments.
Interested in this subject? Find out more information here:
Fischer R.A., Byerlee D. and Edmeades G.O. 2014. Crop yields and global food security: will yield increase continue to feed the world? ACIAR Monograph No. 158. The Australian Centre for International Agricultural Research: Canberra. Access at http://aciar.gov.au/publication/mn158
Since the minimum yield gap, due to considerations of costs and risk, is around 30 percent (of farm yield), the scope for further yield gap closing is more limited in wheat than in the other major cereals, which, in contrast to wheat, showed many larger yield gaps, especially in developing countries.
Besides, the gap-causing constraints in the cases of wheat are generally multiple, related to small deficiencies in soil fertility, weeds and disease management and in the timing of operations. This puts special pressure in the case of wheat on lifting potential yield progress, and justifies substantial increases in research in this area. There is certainly no sign that a biological limit in wheat potential yield has been reached, and several new tools and strategies of sufficient promise are available to justify such investment.
Finally, although increasing carbon dioxide is probably lifting both potential and farm yields of wheat about 0.2 percent a year, it is suggested that out to 2050, this will be cancelled by the negative effect of mean temperature increase, which is now becoming more evident.