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

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 springwheat. The soil CO2 flux peaked immediately after planting, fertilization, and intense precipitation (>15mmin 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 withWP than CWat 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.