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Summary The growth of agricultural production worldwide has led to an increasing role of agro-ecosystems within the global carbon cycle. Arable land in the world covers about one-tenth of the 134 × 1012 m2 of total land area (excluding Antarctica). Much of this land area is bare rock, desert, or covered with ice, and about two-thirds can be considered as covered by vegetation. The total annual carbon flux through all terrestrial ecosystems is estimated at about 50 Pg C (Minami et al., 1993). The objective of this paper is to estimate the contribution of agricultural crops in this total carbon flux. In addition to arable land, grasslands are used for agricultural purposes. They are mainly used for grazing by cattle and sheep, at stocking densities that vary enormously, with the extensively managed rangelands of Australia or Latin America on one end of the scale and the "green carpets" of The Netherlands on the other. Grasslands cover about one-third of the vegetated area and contribute about one-fifth to the global carbon cycle (Minami et al., 1993). For further details on primary productivity of grasslands, reference is made to chapter 12, this volume. Here we present some data on the production of the major crop groups in terms of carbon and nitrogen. The decadal time trend is analyzed, the relation with nitrogen fertilizer production is indicated, and productivity is discussed in relation to other growth-limiting factors.