Table 2.

Inputs and outputs of nitrogen and phosphorus in three corn cropping systems with similar yield potential: a low-input corn-based system in western Kenya; a highly fertilized wheat-corn double-cropping system in north China; and a corn–soya bean rotation in IL, USA. Actual yields of corn were 2000, 8500 and 8200 kg ha⁻¹ yr⁻¹ per crop in the Kenya, China and USA systems, respectively; the Chinese and USA systems also yielded wheat and soya bean, respectively, in a separate cropping season. From Vitousek et al. (2009).

inputs and outputs	nutrient balances by region (kg ha−1 yr−1)
	western Kenya		north China		midwest USA
	N	P	N	P	N	P
fertilizer	7	8	588	92	93	14
biological N fixation					62
total agronomic inputs	7	8	588	92	155	14
removal in grain and/or beans	23	4	361	39	145	23
removal in other harvested products	36	3
total agronomic outputs	59	7	361	39	145	23
agronomic inputs minus harvest removals	−52	+1	+227	+53	+10	−9