Table 1.

Global fluxes of reactive nitrogen introduced into watersheds, commercially exchanged between watersheds and exported by the rivers at their outlet in 1970 and 2000, as derived from the GlobalNEWS database (inputs) and model (river delivery).

(all in Tg N yr−1)	1970	2000
natural N2 fixation	102	99
crop N2 fixation	27	30
fertilizer application	27	80
atmospheric deposition (oxidized N)a	28	34
total NANI	82	144
commercial exchange of food and feedb	11	16
river delivery to the sea	37	43

^aThe available data are for total (red + ox) N. The oxidized N emissions have been considered to roughly amount to half this total.

^bThe sum of the difference (autotrophy−heterotrophy = export (or import) of agricultural goods) for all the watersheds is close to zero, indicating the internal consistency of the data (sum of imports = sum of exports). The total commercial exchange is calculated as half the sum of the absolute value of this difference for all watersheds.