Diversified No‐Till Crop Rotation Reduces Nitrous Oxide Emissions, Increases Soybean Yields, and Promotes Soil Carbon Accrual

Core Ideas Diversification of established no‐till, rain‐fed crop rotations was examined. Mean daily N 2 O fluxes were 24% lower in 4‐yr vs. 2‐yr rotation. Both no‐till rotations (2‐yr and 4‐yr) accrued soil C over this time span. 4‐yr rotation accrued soil C earlier and deeper than 2‐yr rotation. Soybean yields were 22% higher in 4‐yr vs. 2‐yr rotation. The effect of crop rotational diversity on greenhouse gas (GHG) emissions has been explored in several studies, although rarely have measurements been made on whole rotations consisting of two or more crops. We evaluated the impact of crop rotational diversity on GHG emissions, soil organic carbon (SOC), and crop yields over a 4‐yr period in eastern South Dakota, USA. Under no‐till, rain‐fed conditions, a 2‐yr (corn [ Zea mays L.]–soybean [ Glycine max (L.) Merr.]) rotation and a 4‐yr rotation (corn‐field peas [ Pisum sativum L.]–winter wheat [ Triticum aestivum L.]–soybean) were established in a randomized, complete block design (each crop present each year) 8 yr prior to the current study. Average daily N 2 O fluxes were 24% lower ( P = 0.0313) for the 4‐yr rotation (2.34 ± 0.56 g N 2 O‐N ha –1 d –1 ) compared with the 2‐yr rotation (3.06 ± 0.59 g N 2 O‐N ha –1 d –1 ). Significantly elevated N 2 O flux peaks were observed in June of every year and every phase of the 2‐yr rotation, but only in one of 4 yr (corn phase) in the 4‐yr rotation. There was no significant difference in average daily CH 4 flux between the two rotations. Over this 4‐yr period, SOC increased in the 0‐ to 15‐cm depth interval for the 2‐yr rotation, but increased in both the 0‐ to 15‐ and 15‐ to 30‐cm depth intervals for the 4‐yr rotation. Corn yields (6.75 Mg ha –1 ) did not differ between the two rotations. However, the yield of soybean in the 4‐yr rotation (2.87 Mg ha –1 ) was 22% greater ( P = 0.0001) than soybean within the 2‐yr rotation (2.35 Mg ha –1 ). Diversified rotations can decrease N 2 O emissions, increase or accelerate SOC gains, distribute soil C gains deeper in the soil profile, and boost soybean yield.