Tillage, Cropping Sequence, and Nitrogen Fertilization Effects on Dryland Soil Carbon Dioxide Emission and Carbon Content
- Upendra M. Sainju *,
- Jalal D. Jabro and
- Thecan Caesar-TonThat
Management practices are needed to reduce dryland soil CO2 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 soil surface CO2 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 barley–pea (Pisum 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 CO2 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 CO2 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 CO2 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 CO2 flux 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 flux similar to that in the CTB-F sequence.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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