Table 3. Impact of the warming-drying trend (WDT) and the amount of fertilizer on water use efficiency in wetter and drier years in different periods in semiarid area of northern China (SAC).

site	year	crop	period	Tmax	Tmin	PDSI	Fertilizer	WUE
				(°C)	(°C)		(kg ha-1)	(g m-2 mm-1)
Wuchuan	wetter-year	spring wheat	I	21.4 a	-	1.29	19.5 a	0.30 a
			II	21.5 a	-	-0.52	80.4 b	0.56 b
		naked oat	I	23.5 a	-	1.29	16.3 a	0.14 a
			II	23.6 a	-	-0.52	67.0 b	0.30 b
		potato	I	22.6 a	-	1.29	39.0 a	0.64 a
			II	22.7 a	-	-0.52	160.8 b	1.01 b
Wuchuan	drier-year	spring wheat	I	21.8 a	-	-1.36	25.9 a	0.45 a
			II	23.0 b	-	-2.23	73.4 b	0.61 a
		naked oat	I	23.8 a	-	-1.36	21.6 a	0.32 a
			II	25.1 b	-	-2.23	61.2 b	0.38 a
		potato	I	22.0 a	-	-1.36	51.8 a	0.85 a
			II	24.2 b	-	-2.23	146.9 b	1.11 a
Guyuan	wetter-year	spring wheat	I	-	8.2 a	1.16	25.9 a	0.38 a
			II	-	10.5 b	0.27	83.7 b	0.61 b
		potato	I	-	8.8 a	1.16	112.1 a	0.63 a
			II	-	9.2 a	0.27	310.2 b	1.03 b
		maize	I	-	8.6 a	1.16	168.2 a	0.53 a
			II	-	10.3 b	0.27	439.1 b	1.24 b
Guyuan	drier-year	spring wheat	I	-	9.4 a	-1.84	37.0 a	0.68 a
			II	-	10.6 b	-2.46	107.0 b	0.78 a
		potato	I	-	9.2 a	-1.84	160.5 a	0.95 a
			II	-	9.4 a	-2.46	399.3 b	1.09 a
		maize	I	-	9.2 a	-1.84	240.8 a	1.19 a
			II	-	10.3 b	-2.46	566.8 b	1.43 a

I means the years of 1983–1999; II means the years of 2000–2010. Columns labeled with the different letter are significantly different (P<0.05).