ABSTRACT

During the International Biological Program (IBP) of the late 1960s to mid1970s, reviews of nutrient cycling in semiarid and arid environments were commissioned (Charley, 1977; Clark et aI., 1978; Jones and Woodmansee,'- 1979; Kovda et aI., 1979; Binet, 1981; West, 1981; Stewart et aI., 1983) and new research launched, focusing mainly on nitrogen (N)(West and Skujiqs, 1978; Woodmansee, 1978, 1979; Woodmansee et aI., 1981; Bate, 1981; SkujiJ;ls, 1981; O'Connor, 1983). These earlier reviews considered the pre-1980 literature and IBP results then at hand and offered generalizations possible at that time. They also pointed out some remaining problems and researchable topics obvious at that point. Since then, rapid conceptual and technological advances have made possible new ways of investigating nutrient cycles. Improved means of peering at the world and communicating changes in its environment, aswell as intensifying land use, . have led us now to focus on larger, issues (Rosswall et aI., 1988). Thus,' at the start of the International Geophysical' Biological Program (IGBP), it behooves us to re-examine our progress on this topic since the end of IBP, attempt refined generalizations, and point out important unresolved questions to help researchers plan efforts into the 1990s.