ASRU Study for Greenhouse gas Reduction through Agricultural Carbon Enhancement network in Sidney, Montana

Information is needed to mitigate dryland soil greenhouse gas (GHG) emissions by using novel management practices. We evaluated the effects of cropping sequence and N fertilization on dryland soil temperature and water content at the 0- to 15-cm depth and surface CO2, N2O, and CH4 fl uxes in a Williams loam (fi ne-loamy, mixed, superactive, frigid, Typic Argiustolls) in eastern Montana. Treatments were no-tilled continuous malt barley (Hordeum vulgaris L.) (NTCB), no-tilled malt barley–pea (Pisum sativum L.) (NTB–P), and conventional-tilled malt barley–fallow (CTB–F) (control), each with 0 and 80 kg N ha–1. Gas fl uxes were measured at 3 to 14 d intervals using static, vented chambers from March to November 2008 to 2011. Soil temperature varied but water content was greater in CTB–F than in other treatments. The GHG fl uxes varied with date of sampling, peaking immediately after substantial precipitation (>15 mm) and N fertilization during increased soil temperature. Total CO2 fl ux from March to November was greater in NTCB and NTB–P with 80 kg N ha–1 than in other treatments from 2008 to 2010. Total N2O fl ux was greater in NTCB with 0 kg N ha–1 and in NTB–P with 80 kg N ha–1 than in other treatments in 2008 and 2011. Total CH4 uptake was greater with 80 than with 0 kg N ha–1 in NTCB in 2009 and 2011. Because of intermediate level of CO2 equivalent of GHG emissions and known favorable effect on malt barley yield, NTB–P with 0 kg N ha–1 might mitigate GHG emissions and sustain crop yields compared to other treatments in eastern Montana. For accounting global warming potential of management practices, however, additional information on soil C dynamics and CO2 associated with production inputs and machinery use are needed. 2008, greater in cropping than in fallow phases, and greater in NTCB than in NTB-F. Tillage did not infl uence crop biomass and CO2 fl ux but N fertilization had a variable eff ect on the fl ux in 2008. Similarly, soil total C content was not infl uenced by treatments. Annual cropping increased CO2 fl ux compared with crop–fallow probably by increasing crop residue returns to soils and root and rhizosphere respiration. Inclusion of peas in the rotation with malt barley in the no-till system, which have been known to reduce N fertilization rates and sustain malt barley yields, resulted in a CO2 fl ux similar to that in the CTB-F sequence.