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Title:   Author  item
                                            Sainju, Upendra
  Submitted to: Journal of Environmental Protection
                                    Publication Type: Peer Reviewed Journal
                                    Publication Acceptance Date: 5/28/2015
                                    Publication  Date: 9/25/2015
                                    Citation: Sainju, U.M. 2015. Comparison of net global warming potential and greenhouse gas intensity affected by management practices in two dryland cropping sites. Journal of Environmental Protection. 6:1042-1056. doi:10.4236/jep.2015.69092.Interpretive Summary: Agricultural practices produce three soil greenhouse gases (GHGs - carbon dioxide, nitrous oxide and methane) that significantly contribute to radiative forcing of earth’s atmosphere for global warming. While soil carbon (C) sequestration acts as the sink, chemical inputs used for increasing crop yields and farm operations can produce carbon dioxide, thereby reducing the GHG mitigation potential. The balance between carbon sequestration and nitrous oxide and methane emissions as well as carbon dioxide emissions from chemical inputs and farm operations controls net global warming potential (GWP) and greenhouse gas intensity (GHGI). Little is known about the effect of management practices on GWP and GHGI that account for all sources and sinks of GHG emissions in dryland cropping systems. 
The objective of this study was to compare the effect of a combination of tillage, cropping system, and nitrogen (N) fertilization on GWP and GHGI under dryland cropping systems with various soil and climatic conditions from 2008 to 2011 in western North Dakota and eastern Montana, USA. Treatments in western North Dakota with sandy loam soil and 373 mm annual precipitation were conventional till malt barley with 67 kg N/ha (CTB/N1),  conventional till malt barley with 0 kg N/ha (CTB/N0), no-till malt barley-pea with 67 kg N/ha (NTB-P/N1), no-till malt barley with 67 kg N/ha (NTB/N1), and no-till malt barley with 0 kg N/ha (NTB/N0). In eastern Montana with loam soil and 350 mm annual precipitation, treatments were conventional till malt barley-fallow with 80 kg N/ha (CTB-F/N1), conventional till malt barley-fallow with 0 kg N/ha (CTB-F/N0), no-till malt barley-pea with 80 kg N/ha (NTB-P/N1), no-till malt barley with 80 kg N/ha (NTB/N1), and no-till malt barley with 0 kg N/ha (NTB/N0). 
Carbon dioxide sink as soil C sequestration rate at the 0-10 cm depth was greater in NTB-P/N1 and NTB/N1 than the other treatments at both sites and greater in eastern Montana than western North Dakota. Carbon dioxide sources were greater with N fertilization than without and greater with conventional till than no-till. Soil total annual nitrous oxide and methane fluxes varied among treatments, years, and locations. Net GWP and GHGI were lower in NTB-P/N1 than the other treatments in western North Dakota and lower in NTB-P/N1 and NTB/N1 than the other treatments in eastern Montana. Net GWP across similar treatments was lower in eastern Montana than western North Dakota, but GHGI was similar. Annualized crop yield was greater in the treatments with N fertilization than without. 
Because of greater grain yield but lower GWP and GHGI, no-till malt barley-pea rotation with adequate N fertilization can be used as a robust management practice to mitigate net GHG emissions while sustaining dryland crop yields, regardless of soil and climatic conditions. Loam soil reduced GWP and crop yields compared with sandy loam soil.
                                Technical Abstract: Little is known about the effect of management practices on net global warming potential (GWP) and greenhouse gas intensity (GHGI) that account for all sources and sinks of greenhouse gas (GHG) emissions in dryland cropping systems. The objective of this study was to compare the effect of a combination of tillage, cropping system, and N fertilization on GWP and GHGI under dryland cropping systems with various soil and climatic conditions from 2008 to 2011 in western North Dakota and eastern Montana, USA. Treatments in western North Dakota with sandy loam soil and 373 mm annual precipitation were conventional till malt barley (Hordeum vulgarie L.) with 67 kg N/ha (CTB/N1),  conventional till malt barley with 0 kg N/ha (CTB/N0), no-till malt barley-pea (Pisum sativum L.) with 67 kg N/ha (NTB-P/N1), no-till malt barley with 67 kg N/ha (NTB/N1), and no-till malt barley with 0 kg N/ha (NTB/N0). In eastern Montana with loam soil and 350 mm annual precipitation, treatments were conventional till malt barley-fallow with 80 kg N/ha (CTB-F/N1), conventional till malt barley-fallow with 0 kg N/ha (CTB-F/N0), no-till malt barley-pea with 80 kg N/ha (NTB-P/N1), no-till malt barley with 80 kg N/ha (NTB/N1), and no-till malt barley with 0 kg N/ha (NTB/N0). Carbon dioxide sink as soil C sequestration rate at the 0-10 cm depth was greater in NTB-P/N1 and NTB/N1 than the other treatments at both sites and greater in eastern Montana than western North Dakota. Carbon dioxide sources were greater with N fertilization than without and greater with conventional till than no-till. Soil total annual nitrous oxide and methane fluxes varied among treatments, years, and locations. Net GWP and GHGI were lower in NTB-P/N1 than the other treatments in western North Dakota and lower in NTB-P/N1 and NTB/N1 than the other treatments in eastern Montana. Net GWP across similar treatments was lower in eastern Montana than western North Dakota, but GHGI was similar. Annualized crop yield was greater in the treatments with N fertilization than without. Because of greater grain yield but lower GWP and GHGI, no-till malt barley-pea rotation with adequate N fertilization can be used as a robust management practice to mitigate net GHG emissions while sustaining dryland crop yields, regardless of soil and climatic conditions. Loam soil reduced GWP and crop yields compared with sandy loam soil.


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