Integrating beef cattle on cropland affects net global warming potential
Mark A. Liebig, Derek R. Faust, David W. Archer, R.G. Christensen, Scott L. Kronberg, John Hendrickson, J. H. Lee, D. L. Tanaka
Abstract
Abstract Recent interest in integrated crop-livestock (ICL) systems has prompted numerous investigations to quantify ecosystem service tradeoffs associated with management. However, few investigations have quantified ICL management effects on net global warming potential (GWP), particularly in semiarid regions. Therefore, we determined net GWP for grazed and ungrazed cropland in a long-term ICL study near Mandan, ND USA. Factors evaluated for their contribution to net GWP included carbon dioxide (CO 2 ) emissions associated with production inputs and field operations, methane (CH 4 ) emissions from enteric fermentation by beef cattle, change in soil carbon stocks, and soil-atmosphere CH 4 and nitrous oxide (N 2 O) fluxes. Net GWP was significantly greater for grazed cropland (946 kg CO 2equiv. ha -1 yr -1 ) compared to ungrazed cropland (200 kg CO 2equiv. ha -1 yr -1 ) (P=0.0331). The difference in net GWP between treatments was largely driven by emissions from enteric fermentation (602 kg CO 2equiv. ha -1 yr -1 ). Among other contributing factors, CO 2 emissions associated with seed production and field operations were lower under ungrazed cropland ( P = 0.0015 and 0.0135, respectively), while soil CH 4 uptake was greater under grazed cropland ( P = 0.0102). Soil-atmosphere N 2 O flux from each system negated nearly all the CO 2equiv. sink capacity accrued from soil carbon stock change. As both production systems resulted in net greenhouse gas (GHG) emissions to the atmosphere, novel practices that constrain GHG sources and boost GHG sinks under semiarid conditions are recommended.