Table 3.

Yield of winter wheat (t ha⁻¹) given four different amounts of nitrogen fertilizer at four levels of available phosphorus (measured by Olsen's method) in the soil. (Values underlined are the optimum N applications. Adapted from Johnston et al. (2001).)

available P (mg kg−1)	N applied (kg ha−1)
	80	120	160	200
30.4	9.32	9.64	10.12	10.25
19.0	9.37	9.83	10.25	10.30
10.3	8.46	9.14	9.10	9.34
5.0	7.75	7.88	7.85	8.08