Weeds have been a persistent problem in rice since the beginning of settled agriculture. For Asia as a whole, weeds cause an estimated 10-15% reduction in rice yields equivalent to about 50 million tons of rough rice annually.

The papers in this book define the links between the economics of weed control, herbicide use, and weed ecology. The presentations provide a basis for developing a much broader array of weed management tools from which integrated weed management strategies can be designed. Understanding the linkages and developing rational methods are critical in efforts to achieve greater sustainability of rice production.

Weeds have been a persistent problem in rice since the beginning of settled agriculture. For Asia as a whole, weeds cause an estimated 10-15% reduction in rice yields equivalent to about 50 million tons of rough rice annually.

The papers in this book define the links between the economics of weed control, herbicide use, and weed ecology. The presentations provide a basis for developing a much broader array of weed management tools from which integrated weed management strategies can be designed. Understanding the linkages and developing rational methods are critical in efforts to achieve greater sustainability of rice production.

Expansion and intensification of cultivation are among the predominant global changes of this century. Intensification of agriculture by use of high-yielding crop varieties, fertilization, irrigation, and pesticides has contributed substantially to the tremendous increases in food production over the past 50 years. Land conversion and intensification, however, also alter the biotic interactions and patterns of resource availability in ecosystems and can have serious local, regional, and global environmental consequences. The use of ecologically based management strategies can increase the sustainability of agricultural production while reducing off-site consequences.

The race between population and food is a classic theme, yet the outcome of this contest is of enduring contemporary interest. Interestingly, the two variables that are set opposite one another in the race are fundamentally different in character. Population is primarily a stock concept that rises monotonically (when births exceed deaths), whereas food production is overwhelmingly a flow variable that exhibits substantial year-to-year fluctuations. These latter fluctuations, in turn, cause significant economic and nutritional consequences at the household level. The changes are especially important for the poor, even beyond the consequences caused by trend levels of food consumption per capita. In addition, amplifications of price and production variability often produce compensating changes in national food policies. If countries seek to stabilize domestic grain prices, the unintended effect of these actions is further destabilization of global grain markets.

This review explores the potential energy, soil, and water constraints on highly productive agricultural systems. It focuses on the process of agricultural intensification during the past 50 years, and it shows that multiple constraints-as opposed to a single constraint, such as energy-are needed to assess the future sustainability of intensive agricultural production. Recent studies documenting changes in total factor productivity based on long-term experimental trials and field surveys are discussed in detail. The results of these studies are worrisome; they indicate that degradation in soil quality and in the overall natural resource base may threaten the long-run viability of several of the world's most intensive agricultural systems. Other studies are reviewed that support a more optimistic view of resource availability and the ability of improved technology and management to overcome these physical constraints. However, the combined evidence suggests that the increase in agricultural prices required to induce the necessary changes in technology could be devastating to low-income households. Most of the world's poor consume more agricultural output than they produce, and they spend up to 80% of their incomes on food.

Urbanization is now a dominant demographic phenomenon in low- and middle-income countries. By the year 2000, half of the world's population will live in urban areas; of this half, two thirds will be in developing countries, predominantly in Asia. Whether there will be a corresponding shift of poverty from rural to urban areas is the central question of this analysis. Evidence from cross-sectional, time-series, and case data indicates that the percent of poverty in urban areas is dependent on income levels, income growth, and income distribution. The evidence also indicates that the number of poor in rural areas will exceed those in urban areas well into the 21st century. These poverty and urbanization trends are significant politically, and important also with respect to food policy and required investments in agriculture.