Management practices are needed to reduce dryland sod CO(2) emissions and to increase C sequestration We evaluated the effects of tillage and cropping sequence combinations and N fertilization on dryland crop biomass (stems + leaves) and sod surface CO(2) flux and C content (0- to 120-cm depth) in a Williams loam from May to October, 2006 to 2008, in eastern Montana. Treatments were no-tilled continuous malt barley (Hordeum vulgaris L) (NTCB), no-tilled malt bailey pea (Pivot; sativum L) (NTB-P), no-tilled malt barley fallow (NTB-F), and conventional-tilled malt barley fallow (CTB-F), each with 0 and 80 kg N ha(-1) Measurements were made both in Phase I (malt barley in NTCB, pea in NTB-P, and fallow in NTB-F and CTB-F) and Phase II (malt barley in all sequences) of each cropping sequence in every year Crop biomass varied among years. was greater in the barley than in the pea phase of the NTB-P treatment, and greater in NTCB and NTB-P than in NTB-F and CTB-F in 2 out of 3 yr Similarly biomass was greater with 80 than with 0 kg N ha(-1) in 1 out of 3 yr. Soil CO(2) flux increased from 8 mg C m(-2) h(-1) in early May to 239 mg C m(-2) h(-1) in mid-June as temperature increased and then declined to 3 mg C m(-2) h(-1) in September. October Fluxes peaked immediately following substantial precipitation (>10 mm). especially in NTCB and NTB-P Cumulative CO(2) flux from May to October was greater in 2006 and 2007 than in 2008, greater in cropping than in fallow phases, and greater in NTCB than in NTB-F. Tillage did not influence crop biomass and CO(2) flux but N fertilization had a variable effect on the flux in 2008. Similarly, soil total C content was not influenced by treatments Annual cropping increased CO(2) flux compared with crop fallow probably by increasing crop residue returns to sods and root and rhizosphere respiration Inclusion of peas in the rotation wills malt barley in the no-till system, which have been known to reduce N fertilization rates and sustain malt barley yields, resulted in a CO(2) flux similar to that in the CTB-F sequence
