Table 1.

N input and output terms for agricultural (agr.) land and natural (nat.) ecosystems for 1900, 1950, 1970, 2000 [11] and for 2030 and 2050 for the four Millennium Ecosystem Assessment scenarios [13].

year/scenario	agriculture								natural ecosystems
	fertilizer (Nfert)	manurea (Nman)	biological fixation (Nfix)	deposition (Ndep)	total N inputs	N withdrawal (Nwithdr)	NH3–N emission (Nvol)	soil N budget agr. (Nbudget)	biological fixation (Nfix)	deposition (Ndep)	soil N budget nat. (Nbudget)
	N (1012 g yr−1)
1900	1	36	14	6	56	34	6	16	75	24	99
1950	4	52	23	13	93	52	10	30	63	23	86
1970	29	76	30	26	161	78	18	66	57	31	88
2000	83	101	39	36	258	112	33	113	53	33	86
2050GO	119	190	55	49	412	202	59	152	52	46	98
2050TG	98	155	57	33	343	182	48	113	46	26	72
2050AM	75	144	55	44	318	169	42	108	51	39	90
2050OS	109	163	56	51	378	179	51	147	49	39	88

^aExcluding manure N that ends outside the agricultural system, such as manure stored in lagoons or used as fuel or building material (in 2000 this was 11 Tg N).