Soil carbon dioxide and methane emissions and carbon balance with crop rotation and nitrogen fertilization

Highlights: • Soil CO₂ emissions peaked after planting, fertilization, and intense precipitation. • Soil CO₂ emissions decreased with legume-nonlegume crop rotation and reduced N rate. • CH₄ uptake occurred during the winter in 1 out of 4 yr in all treatments (2015–2016). • Yield-scaled CO₂ emissions was unaffected by treatment, but varied by year. • Dryland wheat-based cropping system is a C source without treatment effect. Quantifying soil CO₂ and CH₄ emissions and C balance under dryland cropping systems in arid and semiarid regions is needed to understand their contributions to climate change. The objective of this study was to examine the effect of crop rotation and N fertilization rate on soil CO₂ and CH₄ fluxes and C balance under dryland farming from 2012 to 2016 in the northern Great Plains, USA. Treatments were two crop rotations (continuous spring wheat [Triticum aestivum L.], CW; and spring wheat-pea [Pisum sativum L.], WP) and four N fertilization rates (0, 50, 100, and 150 kg N ha⁻¹) applied to spring wheat. The soil CO₂ flux peaked immediately after planting, fertilization, and intense precipitation (>15 mm in a day) when the emissions varied among treatments. Treatment did not affect soil CH₄ uptake, except that the uptake varied with N fertilization rate in 2015–2016. Cumulative annual soil CO₂ flux was 35–55% greater with CW than WP at 50–150 kg N ha⁻¹ in 2013–2014 and 2015–2016, but was 37% greater with WP than CW at 100 kg N ha⁻¹ in 2014–2015. Mean cumulative soil CH₄ flux was 34% greater with CW than WP at 0 kg N ha⁻¹, but was 16% greater with WP than CW at 150 kg N ha⁻¹. Yield-scaled soil CO₂ and CH₄ fluxes were unaffected (P > 0.05) by treatments, but varied among years. Carbon balance was negative and unaffected by treatments. Results showed that soil CO₂ emissions can be reduced by using legume-nonlegume crop rotation with reduced N fertilization rate with limited impact on soil CH₄ emissions. Dryland spring wheat-based cropping systems was a carbon source in the semiarid region.