Table 1.

Average grain yields and total N losses of the optimum N fertilization (ON) compared with farmers' N practices (FN) (Field Study 1 and 2).

Crop and site of field experiment	N fertilization	N rate		Grain yield		Total fertilizer N loss*
		Rate, kg of N per hectare	Ratio of FN to ON	Yield, kg·ha−1	Ratio of FN to ON	Total loss, kg of N per hectare	Ratio of FN to ON
Rice in Taihu (n = 26)	ON†	200		8,270		102
	FN	300	1.5	8,012	0.97	174	1.7
Wheat in Taihu (n = 9)	ON†	153		3,700		76
	FN	250	1.6	4,084	1.10	155	2.0
Wheat in NCP‡ (n = 121)	ON§	128		6,024		25
	FN	325	2.5	5,764	0.96	71	2.8
Maize in NCP‡ (n = 148)	ON§	158		8,900		52
	FN	263	1.7	8,500	0.95	108	2.1

*Total fertilizer N losses calculated with the models of Fig. 1B simulated from ¹⁵N field experiments.

^†Regional mean optimal N application rate calculated from the mean of economically optimum N rates of field experiments in Taihu regain (5, 12).

^‡Data including Field Study 1 and also summarized from ref. (15, 16); NCP, North China Plain.

^§In-season nitrogen management based on soil Nmin test on the NCP (8, 13, 15, 16).