Influence of No-Tillage on Soil Organic Carbon, Total Soil Nitrogen, and Winter Wheat (Triticum aestivum L.) Grain Yield

Table 2

Treatment means for grain yield, TSN, and SOC and single-degree-of-freedom orthogonal contrasts between CT and NT treatments at E222 (Stillwater), Oklahoma, USA, 2003–2018.

Treatment	Tillage	N rate (kg·ha^−1)	Grain yield (Mg·ha^−1)^†	TSN (g·kg^−1)^‡	SOC (g·kg^−1)^‡
Treatment means
1	CT	0	1.32	0.80	8.53
2	CT	45	1.53	0.88	9.14
3	CT	90	1.94	0.91	9.61
4	CT	135	2.04	0.97	10.05
CV (%)			49.4	13.5	8.2
1	NT	0	1.70	0.99	12.07
2	NT	45	2.17	1.03	13.15
3	NT	90	2.45	1.11	13.61
4	NT	135	2.59	1.15	14.02
CV (%)			42.3	24.2	38.7
Contrast value
1	CT1 vs. NT1	0	0.1074	0.0247	0.0257
2	CT2 vs. NT2	45	0.0060	0.0705	0.0119
3	CT3 vs. NT3	90	0.0281	0.0180	0.0119
4	CT4 vs. NT4	135	0.0209	0.0345	0.0127
Average	CT vs. NT		<0.0001	<0.0001	<0.0001

CV = coefficient of variation; CT = conventional tillage; NT = no-tillage; TSN = total soil nitrogen; SOC = soil organic carbon; ^†treatment means for grain yield were obtained under CT (2003–2010) and NT (2011–2018); ^‡treatment means for TSN and SOC were obtained under CT (2007–2010) and NT (2011–2014).