Hungry planet: Can we produce more food without expanding agricultural land? – Part 2

Improving soil and water management

Revitalizing degraded soils, which may affect one quarter of the world’s cropland provides an opportunity to boost crop yields. Degradation is particularly severe in drylands, which cover much of Africa and where low soil fertility is a direct threat to food security. Loss of organic matter is a special concern because soils then hold less water and are less responsive to fertilizers, making fertilizer use less profitable.

Agencies in recent years have encouraged African farmers to adopt “conservation agriculture,” which relies on no or reduced tillage (ploughing) of soils and preserving crop residues. These practices can limit soil erosion and may help boost yields modestly in particularly dry areas, but farmers are often reluctant to avoid tillage because of the increased need for weeding or herbicides, and because they often need to use crop residues for livestock feed.

Some of the more promising approaches involve agroforestry, often using nitrogen-fixing trees. Farmers have helped regenerate trees in farm fields across 5 million hectares in the Sahel, boosting yields. Commitments to agroforestry made by many African governments would benefit from more systematic evaluation of which systems work economically, and where. Micro-dosing crops with small quantities of fertilizer and trapping water on farms through various blocking systems also shows promise in drylands.

Strategies to improve soils will need to address the real obstacles facing farmers. Rebuilding soil carbon may require diversion of land, labour, or residues needed for food production and will therefore need financial support.

Planting and harvesting existing cropland more frequently, either by reducing fallow land or by increasing double cropping, could in theory boost food production without requiring new cropland. Some analysts have interpreted FAO data to suggest a large recent increase in cropping intensity, but these claims are mostly undercut by local satellite studies. Using relatively crude criteria, other studies have suggested a substantial theoretical potential to increase double cropping on rainfed lands. But roughly half of double-cropped land today is irrigated, and farmers probably plant two crops a year on only 6 percent of rainfed area. Practically and economically, the prospects for expanding double cropping on rainfed lands must therefore be limited, as is expanding double cropping on irrigated land because of water constraints.

In addition, there are significant environmental costs in some regions to planting fallow croplands more frequently because some fallow lands are either in very long-term rotations or are in the early stages of abandonment. Typically, they will revert to forest or grassland and help store carbon and provide other ecosystem services. Planting them more frequently sacrifices these benefits. Despite difficulties, there are opportunities for progress. Raising cropping intensity is a promising option, particularly in Latin America, where double cropping has been growing. The World Resources Institute baseline assumes a 5 percent increase in cropping intensity to 87 percent. If cropping intensity were to increase another 5 percent, the land gap would shrink by 81 million hectares, or 14 percent. Strategies to encourage higher cropping intensity require scientists to conduct more detailed and spatially explicit analyses to determine realistic potential increases in cropping intensity. Studies should account for limitations on irrigation water availability and build in at least some basic economics. Governments and researchers will then be better able to determine which improvements in infrastructure or crop varieties can contribute to economically viable increases in cropping intensity.            

Adapting to climate change

The global impacts of climate change on agriculture are sufficiently uncertain that we did not attempt to model them in our 2050 baseline. Although earlier analyses suggested that effects on crop yields by 2050 might even be beneficial, by the time of the 2014 IPCC report, models projected on average that, without adaptation, global crop yields were “more likely than not” to decline by at least 5 percent by 2050 – with even steeper declines by 2100. Many estimates are even larger, and uncertainty should be a cause for greater concern because “medium” impacts are not more likely.