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Natural Environment

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

Net-zero expansion of agricultural land is a vital pillar of climate targets. Sustained global population growth dictates that food production processes must be optimised if we are to feed our hungry planet.

Tim Searchinger, World Resources Institute and Princeton University
17 August 2020

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.

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.

Efforts to grow more legumes to fix nitrogen in African soils must overcome high rates of disease, which requires breeding plants with improved disease resistance. Enhancing soil carbon also requires that farmers add or fix enough nitrogen to meet crop needs and those of soil-building microbes, so cheaper fertilizers must be available.

  • In drylands like the Sahel, governments and international aid agencies should increase support for rainwater harvesting, agroforestry, farmer-to-farmer education, and reform of tree-ownership laws that can impede farmers’ adoption of agroforestry.
  • Elsewhere, governments and aid agencies need to explore new models for regenerating soils. One option may be to provide financial help to farmers to work incrementally on their farms, improving one small piece of land at a time. If one small area can be improved quickly to the point where it generates large yield gains, the economic return may come soon enough to motivate farmer efforts.

Planting existing cropland more frequently

Food and Agriculture Organization of the United Nations (FAO) data indicate that more than 400 million hectares of cropland go unharvested each year, suggesting that this amount of land is left fallow. FAO data also indicate that farmers plant roughly 150 million hectares twice or more each year (known as double cropping). The ratio of harvests each year (harvested area) to quantity of cropland is known as the “cropping intensity,” a ratio that FAO currently estimates at 82 percent.

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.

IPCC climate models project that, on average, global crop yields are ‘more likely than not’ to decline by at least 5 percent by 2050 – with even steeper declines by 2100.

We modelled one plausible estimate of a 10 percent decline in crop yields due to climate change without adaptation. Cropland would need to expand overall by 457 million hectares (increasing the total land gap by 45 percent). Climate change will benefit some crops, at least in the short term, as higher concentrations of carbon dioxide increase the efficiency of photosynthesis. Warmer temperatures will extend the growing season in colder countries and regional shifts in rainfall patterns will make some locations wetter.

Some areas, though, will become drier and hotter. Higher temperatures will harm crops by drying soils, accelerating water loss, and increasing pest damage. Extreme heat events will harm maize, wheat, coffee, and many other crops by interfering with reproduction. Growing seasons in parts of sub-Saharan Africa could become too short or too irregular to support crops, contributing to major food security concerns. The evidence from crop models indicates significant but uncertain capacity to adapt using tailored crop varieties. Uncertainties about local climate change suggest broad “no regrets” strategies. For example, closing yield gaps in Africa and India would increase incomes and provide a buffer against adverse climate impacts, forest protection could increase resilience through improved local hydrology, while safety-net programmes for the rural poor will better equip small farmers to deal with future variability.    

Some climate effects, however, are sufficiently clear to emphasize the need for new measures or expanded effort on other menu items.

Farmers need effective regional crop-breeding systems that enable them to select alternative crop varieties specifically adapted to local conditions. Small-scale irrigation and water conservation systems will help farmers cope with rainfall variability. Research organizations and companies must breed new traits to overcome highly likely big climate challenges such as high temperature effects on maize, wheat, rice, and coffee. Finally, governments must help fund adaptation to those major physical changes that are clearly predictable, such as altering production systems in areas that will be affected by sea level rise.

This is an excerpt from the report: Creating a sustainable food future produced by the World Resources Institute.

Download the full report