Environmentally Smart Nitrogen Performance in Northern Great Plains’ Spring Wheat Production Systems

Table 4

Effect of at N source and preplant and topdress N rate on spring wheat grain protein Conrad, Corvallis and Kalispell, 2011–2013 growing seasons.

Effect	Conrad			Corvallis			Kalispell
	2011	2012	2013	2011	2012	2013	2011	2012
N source, kg ha^−1	%
Urea	9.4	12.9	13.6	14.8	13.4	16.7	12.6	13.8
ESN	10.0	12.0	14.1	14.9	12.9	16.8	12.4	14.2
Blend	9.9	12.5	13.8	14.9	12.7	16.8	12.4	14.4
Prob >	0.0501	<0.001	0.011	0.732	0.123	0.887	0.656	<0.001
At-seeding N rate, kg ha^−1
0	9.1	9.6	11.0	13.9	13.1	14.7	11.2	12.8
Low^†	9.1	11.1	13.0	14.4	12.7	16.4	11.7	13.9
Medium	9.3	12.7	14.1	15.6	13.4	16.6	13.1	13.9
High	9.9	13.6	14.4	15.6	13.0	17.3	13.8	14.6
Prob > (trend)	0.013^‡	<0.001^‡	<0.001^‡	<0.001^‡	0.078	0.003^‡	<0.001^‡	<0.001^‡
Topdress N rate, kg ha^−1
0	9.4	12.1	13.6	14.4	13.0	16.9	12.1	14.4
45	9.5	12.9	14.1	15.3	13.0	16.6	12.9	13.9
Prob >	0.918	0.001	0.001	0.001	0.968	0.251	0.001	0.001

Down a column for each site-year source means followed by different letter are significant at .
At-seeding N rates: low, medium, and high were 56, 112, and 168 kg ha⁻¹ for Conrad and 112, 224, and 336 kg ha⁻¹ for Corvallis and Kalispell.
Significant linear trend, for at-seeding N rate for each site-year.
Down a column for topdress N rates, LS means followed by different letters are significant at for each source.