ABSTRACT
The ancients calculated yield as the ratio of grain harvested to that sown. Today’s farmers have little opportunity to add fertile land to the world’s cultivated area. But since 1985, UK wheat yields have fluctuated around 7 tons per hectare, showing little evidence of a continuing rapid rise. Despite the astounding gains in molecular biology, which provides the foundation for harnessing the potential of biotechnology, expansion of food output through this new technique thus far has been limited. In some ways, the dramatic yield gains of the last generation or so are like the gains in life expectancy. Those that lack water are severely handicapped in efforts to dramatically raise yields. In summary, there are innumerable small opportunities for raising land productivity, many of them locally unique. But the present identifiable technologies for further raising yields in agriculturally advanced countries are relatively small.
