Measurement of Net Global Warming Potential in Three Agroecosystems

Abstract

When appraising the impact of food and fiber production systems on the composition of the Earth's atmosphere and the 'greenhouse' effect, the entire suite of biogenic greenhouse gases -carbon dioxide (CO 2 ), methane (CH 4 ), and nitrous oxide (N 2 O) -needs to be considered. Storage of atmospheric CO 2 into stable organic carbon pools in the soil can sequester CO 2 while common crop production practices can produce CO 2 , generate N 2 O, and decrease the soil sink for atmospheric CH 4 . The overall balance between the net exchange of these gases constitutes the net global warming potential (GWP) of a crop production system. Trace gas flux and soil organic carbon (SOC) storage data from long-term studies, a rainfed site in Michigan that contrasts conventional tillage (CT) and no-till (NT) cropping, a rainfed site in northeastern Colorado that compares cropping systems in NT, and an irrigated site in Colorado that compares tillage and crop rotations, are used to estimate net GWP from crop production systems. Nitrous oxide emissions comprised 40-44% of the GWP from both rain-fed sites and contributed 16-33% of GWP in the irrigated system. The energy used for irrigation was the dominant GWP source in the irrigated system. Whether a system is a sink or source of CO 2 , i.e. net GWP, was controlled by the rate of SOC storage in all sites. SOC accumulation in the surface 7.5 cm of both rainfed continuous cropping systems was approximately 1100 kg CO 2 equivalents ha À1 y À1 . Carbon accrual rates were about three times higher in the irrigated system. The rainfed systems had been in NT for >10 years while the irrigated system had been converted to NT 3 years before the start of this study. It remains to be seen if the C accrual rates decline with time in the irrigated system or if N 2 O emission rates decline or increase with time after conversion to NT.

The southern Brazilian grassland biome: soil carbon stocks, fluxes of greenhouse gases and some options for mitigation

“…Tillage systems and crop rotations had a significant effect on CO 2 -C retention rates and N 2 O fluxes, while typically low CH 4 fluxes were observed among all soil management systems in this subtropical soil (Figure 4a,b,c). Similar results have been reported for temperate soils by Robertson et al (2000) and Mosier et al (2005Mosier et al ( , 2006 whose results demonstrated that the effect of soil management systems on CO 2 and N 2 O fluxes may drive agricultural soils role as a net source or net sink for GWP.…”

“…An early assessment of soil C stock changes in Southern Brazil verified that 50% of total soil C was lost in a short-time (10-15 years) under conventional tillage in Southern Brazil (Pottker, 1977). Soils usually function as a net source of GHG when native lands are converted to conventionally-managed crop fields (Robertson et al, 2000;Mosier et al, 2005). This behaviour is driven by the fast depletion of C stored in soil as organic matter (SOM), as consequence of a negative balance between net C uptake by plants and C losses to atmospheric CO 2 due to the microbial oxidation of soil organic matter (Amado et al, 2006;Bayer et al, 2006).…”

Measuring and mitigating agricultural greenhouse gas production in the US Great Plains, 1870–2000

“…The implementation of these bestmanagement practices offers the potential for reducing GHG fluxes from Great Plains agricultural systems. Examples of these practices are well known and well documented, and include (i) use of slow-release N fertilizer and nitrification inhibitors with the potential to reduce soil N 2 O fluxes by 14-58% for irrigated and dryland agricultural systems (26), (ii) use of no-tillage cultivation practices that can produce a net C storage of 7.0-20.0 g of C per m −2 ·y −1 for dryland systems (27,28) and 15.0-83.9 g of C per m −2 ·y −1 for irrigated systems (29,30), and (iii) use of new inoculation techniques for cattle that can result in a 20-40% reduction in CH 4 production (7). The adoption of no-tillage farm practices would also reduce the amount of energy consumed by farm equipment and increase both soil water storage and yields in dryland wheat systems.…”

“…The combined impact of best-management practices for Great Plains farming in the 1990s (current GHG fluxes from farming) was determined by (i) assuming that no-tillage practices would lead to an additional storage of 50 g of C per m −2 ·y −1 in irrigated cropping (29,30) and an additional storage of 10.0 g of C per m −2 ·y −1 in dryland cropping (27,28), (ii) a 30% reduction in soil N 2 O fluxes by using improved fertilizer techniques (26), and (iii) a 30% reduction in CH 4 (7) due to improved cattle management (the method of estimation is provided in SI Materials and Methods). Due to the uncertainty of farmer adoption rates, we made our assessments assuming a range of 25%, 50%, 75%, and 100% (44).…”

Mitigating nitrous oxide emissions from a maize-cropping black soil in northeast China by a combination of reducing chemical N fertilizer application and applying manure in autumn

“…The chamber cover (0.58 m × 0.275 m × 0.05 m) was sealed on the chamber base by water during sampling. Air samples were collected in the morning (9:00~10:00) with a 100-mL polypropylene syringe at 0, 15 and 30 min after closing the chambers, and transferred into 500-mL air bags, then N 2 O concentrations in the air samples were determined by gas chromatography (7890A chromatograph equipped with an electron capture detector, Agilent Technologies; Mosier et al 2005). Air samples were usually taken once every 4 d during the maize-growing period, or every day for 5-10 d after each chemical fertilizer application/precipitation event.…”