Table 1. Rates of change in SOC in surface soils, 1998–2014 (mean ± SE).

Fertilizer N*	Change in SOC stocks, 1998–2014†
	No-till continuous corn	Continuous switchgrass	Rotational switchgrass
kg N ha−1 year−1	Mg C ha−1 year−1
0	–	0.9 ± 0.6‡	0.3 ± 0.1
60	0.2 ± 0.3	1.1 ± 0.1‡	1.0 ± 0.2‡
120	0.5 ± 0.3	1.1 ± 0.3‡	1.3 ± 0.5‡
120 + R§	0.7 ± 0.4||	–	–
	Site mean (all N, all crops)		0.8 ± 0.1

*No stock changes were measured in continuous corn under 0 kg N ha⁻¹ year⁻¹.

†Equivalent soil mass approximates top 30 cm of soil (4133 Mg/ha). There were no significant differences between crop type or N rate (P > 0.10).

‡Mean rate was significantly different from zero (P ≤ 0.05).

§“+R” indicates stover retention (0% removal) in continuous corn only.

||Mean rate was marginally significant from zero (P = 0.10).