Impacts of Crop Sequence and Minimum and No-till Cropping Systems on Soil Carbon Stocks in South-Central North Dakota, USA.

Impacts of crop sequence and minimum and no-till cropping systems on soil carbon stocks in south-central North Dakota, USA.

Jonathan J. Halvorson, Mark A. Liebig, David W. Archer, and Donald L. Tanaka

Northern Great Plains Research Laboratory, P.O. Box 459, Mandan, ND 58554-0459, USA

Increased emphasis has been placed on developing agroecosystems that are robust, highly productive, economically competitive, and environmentally benign. After 18 years of a study to evaluate effects of crop sequence and tillage, we measured soil properties at various depths to 3 feet (91.4 cm) and estimated soil carbon. The experiment, located near Mandan, ND, was designed as a split-plot, with crop sequence as whole plots and tillage (minimum tillage or no-till) as subplots. Crop sequences included continuous spring wheat (Triticum aestivum L.) with crop residue left on the soil surface or with crop residue removed, spring wheat–millet (Setaria italica (L.) Beauv.), spring wheat–safflower (Carthamus tinctorius L.)–fallow, spring wheat–safflower–rye (Secale cereale L.), and spring wheat–fallow. Stocks of soil organic carbon calculated by the equivalent mass method (SOC_em) were slightly but significantly higher (P<0.001, paired t-test) than those calculated by the fixed depth method. Greatest disparities between the two methods, detected near the soil surface, were attributable to the effects of tillage. Stocks of SOC_em were not affected by cropping sequence at any partition depth nor by tillage at cumulative depths less than 30.5 cm, and averaged about 26, 47, 73, 114 and 156 Mg ha^-1 in the 0–7.6, 0–15.2, 0–30.5, 0-61.0, and 0-91.4 cm partitions. However significantly more SOC_em was observed under no-till than minimum tillage in both the 0-61 (115.4±2.0 vs 111.8±1.9 Mg ha^-1) and the 0-91.4 cm partitions (158.3 ±2.2 vs153.4 ±2.3 Mg ha^-1) (P<0.05). Organic C in the 0-7.6 cm depth had increased in 2012 by about 3.2 Mg ha^-1 or 16% since 2001.