Abstract
Much of the debate over world agricultural futures centers on the issue of yield growth. `Optimists' in the field base their analyses on a technology- and input-driven rate of increase in yields which, they argue, has outpaced population growth and will continue to do so, leaving a margin for steady increase in per capita incomes. Those who are sometimes classified as `pessimists' (we prefer the term `ecological realists') see practical limits to global and regional carrying capacity in agriculture, and maintain that the world is close to, or may even have passed, these limits. Projections for world agriculture in the first half of the twenty-first century vary widely, largely depending on assumptions on yield growth. We investigate the pattern of yield growth for major cereal crops, and present evidence that the growth pattern is logistic, not exponential. This pattern is consistent with ecological limits on soil fertility, water availability, and nutrient uptake. Projections for supply and demand in the twenty-first century based on a logistic rather than an exponential model of yield growth imply that the world is indeed close to carrying capacity in agriculture, and that specific resource and ecological constraints are of particular importance at the regional level. A supply-side strategy of increased production has already led to serious problems of soil degradation and water overdraft, as well as other ecosystem stresses. This implies that demand-side issues of population policy and efficiency in consumption are crucial to the development of a sustainable agricultural system.
Published Version
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