CAUSES OF SLOWING PRODUCTIVITY GAINS.

World crop yield growth has slowed dramatically during the last decade, which suggests that world food supplies will tighten in the future. A recent report on soil fertility helps explain why yield growth is slowing.

Degradation of soils around the world is one reason given for the slowing growth in global crop yields. A recent study by the International Food Policy Research Institute (IFPRI) reported serious soil fertility problems and production constraints for much of the world's farmland.

The report indicated that only 16 percent of the world's farmland is free of problems such as low fertility, acidity, chemical contamination or salinity. Almost 30 percent of the farmland in North America is in good condition, compared with less than 6 percent in parts of Asia. Salt deposits and aluminum contamination are serious problems in many parts of the world, and these problems generally are getting worse. Depending on the region, topsoil is being lost to erosion 16 to 300 times faster than it can be replaced.

The IFPRI report concluded that there is an urgent need for farmers to use irrigation water more efficiently. Irrigation still accounts for more than 70 percent of the water used worldwide, but many countries are facing serious water shortages. One-third of the world population lives in countries experiencing moderate to high water stress. The slowdown in the growth in irrigated acres is another factor cutting yield growth.

The rapid growth in the worldwide urban population during the next decade will put even more pressure on the demand for water. The world's urban population is growing at four times the rate of the rural population. Between now and 2025, the number of people living in urban areas is projected to double to more than 5 billion. This growth is especially strong in poor countries. Industrial water use is projected double by 2025. Clearly, the competition for water will intensify in the years ahead, and the returns from water used for industry are typically far higher than returns from agriculture.

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For more information about world agriculture and agriculture-related issues, contact Rich Pottorff, chief economist, Doane Agricultural Services Co., St. Louis, at 314/ 372-3517 or e-mail [e-mail]