The second Green Revolution is underway. Just as the first Green Revolution developed crops responsive to high soil fertility, the second one will produce crops adapted to low soil fertility.

Although researchers have developed livestock with improved rates of gain, plant breeders still need to develop crop varieties with parallel gains in productivity, producing more grain from fewer inputs. In many ways the situation is analogous to our focus on energy efficiency.

The U.S. has been blessed with fertile soils and abundant moisture, allowing plant breeders to focus on diseases and pests.

We need to focus on roots, where plant nutrients are absorbed. Half of all applied nitrogen (N) goes to waste because we don't have crops that grow roots quickly enough to reach that N before it leaches out of the soil profile. So in addition to helping growers become more cost-efficient, developing more efficient corn roots would decrease water pollution. If we could improve the efficiency of the corn crop by 20%, that would be huge.

Although N is the main concern for many of us, world phosphorus (P) reserves will be used up more quickly than world oil reserves. Nitrogen can be extracted from the air, which is 80% N, but once we deplete our reserves of concentrated phosphate ore, they're gone.

Plant breeders in Brazil have incorporated soil adaptation in their selection programs, resulting in varieties tolerant of acid. Tolerance of infertile soils is a critical component of the technology package converting the Brazilian Cerrado to crop cultivation.

For 50 years, crop breeding has focused on yield traits and disease resistance selected under high fertility. Most of the elite lines used today as parents in crossing programs may therefore be unsuited to low-fertility soils.

BY CONTRAST, consider the land-races, varieties developed by traditional farmers, often in low-input systems. They may have many useful traits, but may lack disease resistance, high yield or other traits valued by growers in the industrialized world.

One common evolutionary response to low-fertility environments is more productive root systems. For example, enhanced lateral rooting under P stress may be harnessed as a useful trait for more P-efficient corn genotypes. However, routine field screening of large numbers of genotypes for low-fertility adaptation is generally costly, slow and unproductive.

Vast areas of the developing world have serious soil fertility problems, including soil acidity and aluminum toxicity, and low P, N, calcium and magnesium availability. In Africa, corn yields are only 5% of their potential due to fertility limitations and drought.

Few stakeholders are aware of the potential to develop crops tolerant of low-fertility soils. This is reflected by low prioritization of this activity in national research programs (especially in the U.S.).

This is puzzling, considering the central importance of soil fertility in agricultural production in developing nations, the serious environmental problems caused by over-fertilization in rich countries and decades of research documenting large genetic variation within crop species for soil adaptation.

The combination of a growing world population, land degradation, high fuel and fertilizer costs, dwindling supplies of high-grade P ore and the uncertain effects of global climate change in low-fertility environments will ensure that the need for a second Green Revolution will only increase in coming decades.

Will we rise to this challenge?