The ‘green revolution’ and industrialisation of agriculture led to huge increases in crop production around the world. Now the pressure is on to feed 3 billion extra mouths in the next 40 years while the climate changes and the costs of energy and resources escalate. As a plant geneticist and physiologist, I see the future contribution to be made by plant breeders as valuable, but quantitatively small. Instead, changes in the expectations and actions of people will play the major role in steering us through some challenging decades ahead. Here I summarise some of the issues that will challenge food production and suggest that our greatest need is to recognise that ‘business as usual’ is not an option.

Breeding for yield

The ‘green revolution’ which combined (i) breeding of high-yielding varieties, (ii) the application of fertlilisers and pesticides, (iii) the increased use of irrigation and (iv) cheap transport fuels, led to huge increases in food crop production in the period since the Second World War. Global cereal production has increased three-fold per hectare and in developed countries using energy-intensive agricultural systems, yields of some crops have increased 5 or 10-fold per unit of land.

But what of the future? The IPCC in 2007 assumed global crop yield increases of 80% by 2050, continuing the trend of the post war era. But such increases in yields of some crops have already ceased. Yields of wheat have plateaued and while some gains continue to be made in maize and rice productivity, it is sobering to note that Chinese rice production only increased by 2% per hectare in the period 1997 to 2007 while in the preceding decade it increased by 17% (FAO 2009). Plant breeding has achieved an enormous amount but obviously there is a limit to how much more can be achieved. Modern soybean varieties intercept 90% of the photosynthetically-active solar radiation through the growing season and invest a whopping 60% of their biomass into the harvested seeds. There is no room for improvement there. We might be able to increase the rate of plant growth, but we do not know how to do that (Zhu et al., 2010).

Effects of climate change

Optimists point to the positive effects of increased temperatures and atmospheric CO₂ levels on crop productivity in the future. While it is true that increasing the temperature and CO₂ levels can increase plant productivity in some specific cases (depending on the type of plant and the place), the widely held view among plant physiologists is that any such benefits will be small, and will be outweighed by the negative impacts of higher temperatures, water limitations and extreme weather events (Ainsworth and Ort 2010; Long and Ort, 2010). Growing-season temperatures may be higher than the average (e.g.. a 3^oC average rise could be 4^oC in summer and 2^oC in winter). U.S. maize and soybean production have been predicted to fall by at least 30% by the end of this century under the IPCC scenario with lowest temperature rise. Sporadic heat waves have serious effects on yields such as the +6^oC heat wave in Europe in 2003 which saw record crop losses. Fertility and grain fill are adversely affected by high temperatures.

Effects of energy costs

Coupled with the increasing costs of transport fuels, chemicals and fertilisers as fossil fuel prices escalate, crop production per unit of land will be unable to keep pace with population growth and with the hopes of the people of developing nations. Major increases in crop productivity in developing nations are likely to be constrained by the increasing costs of implementing western-style industrialised agriculture. Thus, increasing demands for more food are likely to be met by clearing more land for agriculture, but such land is likely to be poor quality compared to the food bowls of the U.S. Mid West, Argentina or Europe.

Fertilisers

World agriculture consumes about 100 million tonnes of nitrogen fertilisers per year. Most of this fertiliser is manufactured from natural gas by means of the Haber-Bosch process. The methane (CH₄) of natural gas is oxidised to CO₂ and hydrogen. The hydrogen is then reacted with nitrogen from the air at high temperature and pressure to form ammonia. This process consumes as much as 5% of the world’s natural gas production. And it puts at least 300 million tonnes of CO₂ into the atmosphere every year. Eutrophication, soil acidification and emission of the greenhouse gases nitrous oxide and methane are other consequences of nitrogen fertiliser use.

We use 50 million tonnes of phosphate every year. China and the USA are the world’s biggest producers. The USA produces 19 % but 65 % of that amount comes from mines in Florida which may not last more than a few decades. Meanwhile nearly 40 % of global reserves are controlled by Morocco. The concept of ‘peak phosphate’ is real and we will see prices rise steeply.

Obviously such use of N and P fertilisers cannot be continued indefinitely (they are not ‘renewable’), yet without them, crop production in the industrialised nations will fall dramatically. From the perspective of the environment, using less is preferable. Breeders are already busy trying to select varieties that use N and P more efficiently but by using less, we may still need to compromise on lower yields.

Water

Water dominates crop yields. Warmer temperatures mean more water held in the atmosphere and less rain on average. The loss of some glaciers due to global warming will deprive some rivers of their summer flow. So both rain-fed and irrigated crops will face challenges in the future.  Two targets for plant breeders are drought tolerance and water use efficiency. These are complex traits but some progress is being made to produce plants that can tolerate episodes of drought. However, tolerating drought and growing under drought are two different things.

Migration of crop production

There are two emerging geographical trends in crop production. The most immediate of these is the leasing of land in foreign countries to produce food for import. Korea’s Daewoo Logistics announced in 2009 that it had negotiated a 99-year lease on 3.2 million acres of farmland on Madagascar. That’s nearly half of the arable land, according to the U.N.’s Food and Agriculture Organization (FAO), and Daewoo plans to put about three quarters of it under corn. The remainder will be used to produce palm oil for biofuels. Other developed nations are following suit. In a very recent move, Bangladesh has announced plans to lease crop land in Sub-Saharan Africa in a move that acknowledges its precarious position on food security. It is likely that such arrangements will lead to future tensions between nations if they do not lead to the types of benefits both parties hope for.

The second trend is less obvious and much slower. With global warming, crop producing areas will migrate slowly towards the poles. Thus the wheat belt of North America is predicted to migrate northwards into Canada as temperatures rise. However soil quality further north is less good, so yields may drop. In Australia the wheat belt is moving southwards, but it does not have far to go before it reaches the southern ocean. Eurasia will see a similar migration and this will shift production from one country to its northern neighbour.

Diet

The shift towards high protein diets in developing nations makes further demands on crop production. China imported 1.1 M tonnes of soybeans in 1990 but 33 M tonnes in 2007 (from 1% to 15% of global production).  Meat production can require as much as 5 times as much land to produce the equivalent amount of vegetable food (animals convert plants into meat very inefficiently). Animal production also contributes to methane emissions.

Civil unrest, political instability and conflict between neighbours

We have already witnessed civil unrest resulting from food shortages in Egypt, The Philippines, Haiti and elsewhere. We have seen some countries impose export bans on some of their crop products, to meet domestic demands (such as wheat in Russia and rice in India). There is continued tension between India and Pakistan for the water flowing in the Indus and Chenab river systems – a strategically vital resource for both nations. Countries at war focus more effort on fighting than on growing crops. Whenever civil unrest or conflict develops, productivity is threatened. Wikipedia reports 115 wars since 1990. If food shortages become more acute, then more conflicts will be triggered, and food production will suffer further.

Other threats

Other threats include changes in the distribution and severity of plant pests and disease, rising sea levels, flooding, storms, decline in soil quality (eg erosion, salinity) and diversion of resources into growing energy crops for biofuels rather than food crops. It is ironic that the industrialisation of agriculture was hailed as the ability to transform oil (petroleum) into food, but now we consider trying to do the reverse.

The future

Business as usual is not an option for future food production. Science and technology can help but does not have all the answers. Improved crop varieties will be created but improvements are likely to be incremental rather than transforming. We will need to adjust to different food supplies and expectations. Seasonal food should be appreciated. We will need to make better use of the food we produce. The cost of food will increase with energy costs and people in the West should expect to spend an increasing proportion of their income on food. Presumably as food costs rise, people will be less wasteful. Reducing meat consumption will be beneficial. Growing diverse crops in local communities and regions will become more important. Food produced by ‘people power’ will become increasingly important, relative to food produced industrially. This raises the possibility that developing nations might be better adapted to produce food with low inputs, relative to western nations that are currently hooked on high intensity agriculture.  Continued economic growth is the biggest threat so we need to campaign for population control and less dependence on consumption of energy and resources, particularly water, fossil fuels and minerals.

References

How do we improve crop production in a warming world? Ainsworth EA and Ort DR (2010) Plant Physiology 154, 526-530. http://www.ncbi.nlm.nih.gov/pubmed/20921178

More than taking the heat: crops and global change. Long SP and Ort DR (2010) Current Opinion in Plant Biology 13, 241-248. http://www.ncbi.nlm.nih.gov/pubmed/20494611

Improving photosynthetic efficiency for greater yield. Zhu XG, Long SP and Ort DR (2010) Annual Reviews of Plant Biology, 61, 235-261. http://www.ncbi.nlm.nih.gov/pubmed/20192734