Effect of Irrigation and Preplant Nitrogen Fertilizer Source on Maize in the Southern Great Plains

Table 6

Single degree-of-freedom contrast results for differences in treatment groupings for grain yield, N use efficiency (NUE), and water use efficiency (WUE) for Stillwater, OK (STW), in 2012 and 2013. Results listed under the “Main” column heading are the results of data pooled across irrigated and rain-fed treatments. Values in parenthesis are the difference in mean values for the group after the “versus” subtracted from the mean value of the group before the “versus.”

Contrast	Main	Irrigated	Rain-fed	Main	Irrigated	Rain-fed	Main	Irrigated	Rain-fed
	Grain yield^a			NUE^a			WUE^a
STW 2012
UAN versus AS (difference)	ns^b (−792)	ns (−241)	(−1343)	ns (0.4)	ns (4.8)	ns (−5.7)	—	—	—
UAN linear	ns	**	ns	ns	ns	ns	—	—	—
UAN quadratic	ns	ns	ns	—	—	—	—	—	—
AS linear	**	**	ns	ns	*	ns	—	—	—
AS quadratic	ns	ns	*	—	—	—	—	—	—
STW 2013
UAN versus AS (difference)	(924)	(1463)	ns (385)	ns (4.8)	ns (8.4)	ns (1.3)	(1.4)	(2.1)	ns (0.7)
UAN linear	**	***	ns	ns	ns	ns	**	***	ns
UAN quadratic	ns	ns	ns	—	—	—	ns	ns	ns
AS linear	ns	ns	ns	**	**	ns	ns	ns	ns
AS quadratic	**	**	ns	—	—	—	**	**	ns

Units: grain yield: kg ha⁻¹; NUE: percent; WUE: kg ha⁻¹ mm⁻¹.
^bns: not significant at the 0.10 level.
Significant at the 0.10, 0.05, and 0.01 level, respectively.