Net Global Warming Potential and Greenhouse Gas Intensity Affected by Cropping Sequence and Nitrogen Fertilization

Abstract

Little information is available about management practice effects on the net global warming potential (GWP) and greenhouse gas intensity (GHGI) under dryland cropping systems. We evaluated the effects of cropping sequences (conventional-tillage malt barley [Hordeum vulgaris L.]–fallow [CTB-F], no-till malt barley–pea [Pisum sativum L.] [NTB-P], and no-till continuous malt barley [NTCB]) and N fertilization rates (0 and 80 kg N ha−1) on net GWP and GHGI from 2008 to 2011 in eastern Montana. Carbon dioxide sources from farm operations were greater under CTB-F than NTB-P and NTCB and greater with N fertilization than without, but the sources from soil greenhouse gases (GHGs) varied among treatments and years. Carbon dioxide sinks from crop residue and soil organic C (SOC) sequestration were greater under NTB-P or NTCB with 80 kg N ha−1 than other treatments. Net GWP and GHGI based on soil respiration (GWPR and GHGIR, respectively) and SOC (GWPC and GHGIC, respectively) were greater under CTB-F with 0 kg N ha−1 than other treatments, suggesting that alternate-year fallow and the absence of N fertilization to crops can increase net GHG emissions. Because of greater grain yield but lower GWP and GHGI, NTB-P with N rates between 0 and 80 kg N ha−1 may be used as management options to mitigate global warming potential while sustaining dryland malt barley and pea yields compared with CTB-F with 0 kg N ha−1 in the northern Great Plains. The results can be applied to other semiarid regions with similar soil and climatic conditions.