Abstract
Abstract Crop intensification is often thought to increase greenhouse gas (GHG) emissions, but studies in which crop management is optimized to exploit crop yield potential are rare. We conducted a field study in eastern Nebraska, USA to quantify GHG emissions, changes in soil organic carbon (SOC) and the net global warming potential (GWP) in four irrigated systems: continuous maize with recommended best management practices (CC‐rec) or intensive management (CC‐int) and maize–soybean rotation with recommended (CS‐rec) or intensive management (CS‐int). Grain yields of maize and soybean were generally within 80–100% of the estimated site yield potential. Large soil surface carbon dioxide (CO 2 ) fluxes were mostly associated with rapid crop growth, high temperature and high soil water content. Within each crop rotation, soil CO 2 efflux under intensive management was not consistently higher than with recommended management. Owing to differences in residue inputs, SOC increased in the two continuous maize systems, but decreased in CS‐rec or remained unchanged in CS‐int. N 2 O emission peaks were mainly associated with high temperature and high soil water content resulting from rainfall or irrigation events, but less clearly related to soil NO 3 ‐N levels. N 2 O fluxes in intensively managed systems were only occasionally greater than those measured in the CC‐rec and CS‐rec systems. Fertilizer‐induced N 2 O emissions ranged from 1.9% to 3.5% in 2003, from 0.8% to 1.5% in 2004 and from 0.4% to 0.5% in 2005, with no consistent differences among the four systems. All four cropping systems where net sources of GHG. However, due to increased soil C sequestration continuous maize systems had lower GWP than maize–soybean systems and intensive management did not cause a significant increase in GWP. Converting maize grain to ethanol in the two continuous maize systems resulted in a net reduction in life cycle GHG emissions of maize ethanol relative to petrol‐based gasoline by 33–38%. Our study provided evidence that net GHG emissions from agricultural systems can be kept low when management is optimized toward better exploitation of the yield potential. Major components for this included (i) choosing the right combination of adopted varieties, planting date and plant population to maximize crop biomass productivity, (ii) tactical water and nitrogen (N) management decisions that contributed to high N use efficiency and avoided extreme N 2 O emissions, and (iii) a deep tillage and residue management approach that favored the build‐up of soil organic matter from large amounts of crop residues returned.
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Claims 18
Claim · model-written summary
Maize and soybean yields reached 80–100% of site potential.
Zea maysOrganisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Grain yields of maize and soybean were generally within 80–100% of the estimated site yield potential”
Claim · model-written summary
Soil CO2 fluxes associated with crop growth, temperature and moisture.
Not reportedDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Large soil surface carbon dioxide (CO 2 ) fluxes were mostly associated with rapid crop growth, high temperature and high soil water content”
t0“maize”
Claim · model-written summary
Intensive management did not consistently raise soil CO2 efflux.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Within each crop rotation, soil CO 2 efflux under intensive management was not consistently higher than with recommended management”
t0“maize”
Claim · model-written summary
Soil organic carbon rose in continuous maize systems.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“SOC increased in the two continuous maize systems”
Claim · model-written summary
Soil organic carbon fell in CS-rec.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“decreased in CS‐rec”
e1“SOC increased in the two continuous maize systems, but decreased in CS‐rec”
t0“maize”
Claim · model-written summary
Soil organic carbon remained unchanged in CS-int.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“remained unchanged in CS‐int”
e1“SOC increased in the two continuous maize systems, but decreased in CS‐rec or remained unchanged in CS‐int”
t0“maize”
Claim · model-written summary
N2O peaks associated with heat and soil moisture.
Not reportedDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“N 2 O emission peaks were mainly associated with high temperature and high soil water content resulting from rainfall or irrigation events”
t0“maize”
Claim · model-written summary
N2O peaks related less clearly to soil nitrate.
Not reportedDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“less clearly related to soil NO 3 ‐N levels”
e1“N 2 O emission peaks”
t0“maize”
Claim · model-written summary
Intensive systems only occasionally exceeded recommended N2O fluxes.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“N 2 O fluxes in intensively managed systems were only occasionally greater than those measured in the CC‐rec and CS‐rec systems”
t0“maize”
Claim · model-written summary
Fertilizer-induced N2O emissions were 1.9% to 3.5% in 2003.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Fertilizer‐induced N 2 O emissions ranged from 1.9% to 3.5% in 2003”
t0“maize”
Claim · model-written summary
Fertilizer-induced N2O emissions were 0.8% to 1.5% in 2004.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“from 0.8% to 1.5% in 2004”
e1“Fertilizer‐induced N 2 O emissions”
t0“maize”
Claim · model-written summary
Fertilizer-induced N2O emissions were 0.4% to 0.5% in 2005.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“from 0.4% to 0.5% in 2005”
e1“Fertilizer‐induced N 2 O emissions”
t0“maize”
Claim · model-written summary
Four systems had no consistent differences in fertilizer-induced N2O emissions.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“with no consistent differences among the four systems”
e1“Fertilizer‐induced N 2 O emissions”
t0“maize”
Claim · model-written summary
All four cropping systems were net greenhouse-gas sources.
- Outcome
- net sources of GHGe0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“All four cropping systems where net sources of GHG”
t0“maize”
Claim · model-written summary
Continuous maize had lower GWP than maize–soybean systems.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“continuous maize systems had lower GWP than maize–soybean systems”
Claim · model-written summary
Intensive management did not significantly increase GWP.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“intensive management did not cause a significant increase in GWP”
t0“maize”
Claim · model-written summary
Maize ethanol cut life-cycle emissions by 33–38% against gasoline.
- Outcome
- life cycle GHG emissions of maize ethanole0
- Direction
- reductione0
- Value
- 33–38%e0
- Comparator
- petrol‐based gasolinee0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Converting maize grain to ethanol in the two continuous maize systems resulted in a net reduction in life cycle GHG emissions of maize ethanol relative to petrol‐based gasoline by 33–38%”
Claim · model-written summary
Authors conclude optimized management can keep net GHG emissions low.
- Outcome
- management is optimized toward better exploitation of the yield potentiale0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“net GHG emissions from agricultural systems can be kept low when management is optimized toward better exploitation of the yield potential”
t0“maize”