Table 2. Effects of irrigation and nitrogen application on grain yield and protein content in winter wheat in 2012/2013, 2013/2014 and 2014/2015, and interactions between irrigation and nitrogen application; summary of F significance from analysis of variance of the effects of main factors and interactions.

Treatment	Yield (t ha-1)			Protein (%)
	2012/2013	2013/2014	2014/2015	2012/2013	2013/2014	2014/2015
I0	4.99b	6.16b	6.92c	14.76	15.33	14.33
I1	5.37b	7.19a	7.81b	13.34	14.91	14.33
I2	6.45a	7.74a	8.00a	14.22	14.89	14.35
F-test	**	**	**	ns	ns	ns
N0	4.58b	4.47b	4.80b	11.57c	14.20b	10.86c
N180	5.73a	7.84a	8.41a	14.32b	15.22a	15.17b
N240	6.03a	7.76a	8.55a	14.91ab	15.40a	15.54a
N300	6.08a	8.05a	8.54a	15.62a	15.34a	15.77a
F-test	**	**	**	**	**	**
I0×N0	3.71b	3.57b	4.32b	12.57b	14.37b	11.50b
I0×N180	4.94ab	6.67a	7.73a	15.33a	15.53a	15.10a
I0×N240	5.62a	7.34a	7.81a	15.37a	15.83a	15.10a
I0×N300	5.69a	7.07a	7.81a	15.77a	15.57a	15.60a
F-test	*	**	**	**	**	**
I1×N0	4.46b	4.60b	5.11b	11.50c	13.83b	10.67c
I1×N180	5.58a	8.39a	8.51a	12.40b	15.13a	15.03b
I1×N240	5.76a	7.63a	8.73a	13.93ab	15.30a	15.67a
I1×N300	5.70a	8.13a	8.87a	15.53a	15.37a	15.93a
F-test	**	**	**	**	**	**
I2×N0	5.56b	5.25b	4.98b	10.63b	14.40b	10.40c
I2×N180	6.65a	8.48a	8.99a	15.23a	15.00a	15.37b
I2×N240	6.72a	8.31a	9.11a	15.43a	15.07a	15.87a
I2×N300	6.86a	8.93a	8.93a	15.57a	15.10a	15.77a
F-test	*	**	**	**	**	**
Grand mean	5.60	7.03	7.57	14.11	15.04	14.33
I×N (F-test)	ns	ns	ns	**	ns	**
CV (%)	4.32	6.73	0.57	9.02	0.74	0.55

Note: ns, not significant at P < 0.05;

* Significant at P < 0.05;

** Significant at P < 0.01; Data in the same column with different letters indicate a significant difference at P < 0.05.