Abstract
Introducing cover crops and diversifying annual crop rotations can provide additional carbon (C) input to soils and are practices that have been promoted as climate change mitigation measures. However, year-round field studies are needed to evaluate the net effect on carbon dioxide (CO 2 ) uptake, including consideration of carbon removal from the field during harvest depending on the crop grown to diversify the rotation. In addition, evaluation of net greenhouse gas (GHG) emissions requires accounting for changes in soil nitrous oxide (N 2 O) and CO 2 emissions from production of farm inputs and field operations in the altered crop rotation. In this study, our objectives were to evaluate the annual dynamics of CO 2 exchange and to estimate net GHG emissions for a diverse (DIV) corn-soybean-winter wheat crop rotation that included cover crops and a conventional (CONV) corn-soybean-soybean crop rotation. The year-round net ecosystem exchange (NEE) of CO 2 on two side-by-side 8-ha fields (one under DIV and one under CONV management) was measured using the eddy covariance method over three years (2018–2021) in Ontario, Canada. Results showed that DIV rotation significantly increased cumulative NEE, gross primary production (GPP), and ecosystem respiration (Re) –578, –3750 and 3170 g C m −2 , respectively, compared to the CONV (–501, –3361, 2859 g C m −2 ) over three years. Overall, the DIV rotation resulted in a 15 % increase in NEE compared to CONV. Accounting for the grain C removed during harvest, on an annual basis, DIV and CONV corn and soybean fields were C sources. However, net ecosystem carbon budget (NECB) was a sink (–44 g C m −2 ) for DIV winter wheat + cover crops if only grain was removed and reversed to a C source (197 g C m −2 ) with straw + grain removal. The summed NECB across the three study years revealed that both fields were C sources (NECB > 0). Similarly, the DIV rotation was a net GHG source compared to CONV for straw + grain removal but had similar net GHG emission to CONV when only wheat grain was removed. From the present study, DIV did not reduce the net GHG emissions in the short term (3 years) as expected, but long-term measurements are needed to confirm this trend. Further multi-year eddy covariance and soil carbon stock measurements should be done to design effective diversified crop rotations.
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Claims 11
Claim · model-written summary
DIV rotation significantly increased cumulative NEE relative to CONV.
Verbatim
e0“DIV rotation significantly increased cumulative NEE, gross primary production (GPP), and ecosystem respiration (Re) –578, –3750 and 3170 g C m −2 , respectively, compared to the CONV (–501, –3361, 2859 g C m −2 ) over three years.”
t0“diverse crop rotation using cover crops”
Claim · model-written summary
DIV rotation significantly increased GPP relative to CONV.
Verbatim
e0“DIV rotation significantly increased cumulative NEE, gross primary production (GPP), and ecosystem respiration (Re) –578, –3750 and 3170 g C m −2 , respectively, compared to the CONV (–501, –3361, 2859 g C m −2 ) over three years.”
t0“diverse crop rotation using cover crops”
Claim · model-written summary
DIV rotation significantly increased ecosystem respiration relative to CONV.
Verbatim
e0“DIV rotation significantly increased cumulative NEE, gross primary production (GPP), and ecosystem respiration (Re) –578, –3750 and 3170 g C m −2 , respectively, compared to the CONV (–501, –3361, 2859 g C m −2 ) over three years.”
t0“diverse crop rotation using cover crops”
Claim · model-written summary
DIV rotation had a 15 % increase in NEE compared to CONV.
Verbatim
e0“the DIV rotation resulted in a 15 % increase in NEE compared to CONV.”
t0“diverse crop rotation using cover crops”
Claim · model-written summary
Corn and soybean fields in both rotations were annual carbon sources after accounting for grain carbon removal.
- Taxon
- corn and soybean
Glycine max
Zea mays subsp. mayse0 - Outcome
- C sourcese0
- Qualifier
- grain C removed during harveste0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Accounting for the grain C removed during harvest, on an annual basis, DIV and CONV corn and soybean fields were C sources.”
Claim · model-written summary
DIV winter wheat with cover crops was a carbon sink when only grain was removed.
- Taxon
- winter wheat
Triticum aestivume0 - Outcome
- NECB) was a sinke0
- Value
- –44 g C m −2e0
- Qualifier
- only grain was removede0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“net ecosystem carbon budget (NECB) was a sink (–44 g C m −2 ) for DIV winter wheat + cover crops if only grain was removed”
Claim · model-written summary
DIV winter wheat with cover crops became a carbon source when straw and grain were removed.
- Taxon
- winter wheatTriticum aestivume1
- Outcome
- C sourcee0
- Value
- 197 g C m −2e0
- Qualifier
- straw + grain removale0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“reversed to a C source (197 g C m −2 ) with straw + grain removal.”
e1“DIV winter wheat + cover crops”
Claim · model-written summary
Both rotation fields were carbon sources across three study years.
Verbatim
e0“The summed NECB across the three study years revealed that both fields were C sources (NECB > 0).”
t0“diverse crop rotation using cover crops”
Claim · model-written summary
DIV rotation was a net GHG source relative to CONV with straw and grain removal.
- Taxon
- crop rotationt0
- Treatment
- DIV rotatione0
- Outcome
- net GHG sourcee0
- Qualifier
- straw + grain removale0
- Comparator
- CONVe0
Not reportedDirection
Verbatim
e0“the DIV rotation was a net GHG source compared to CONV for straw + grain removal”
t0“diverse crop rotation using cover crops”
Claim · model-written summary
DIV and CONV rotations had similar net GHG emissions when only wheat grain was removed.
Verbatim
e0“had similar net GHG emission to CONV when only wheat grain was removed.”
t0“diverse crop rotation using cover crops”
e1“the DIV rotation was a net GHG source compared to CONV”
Claim · model-written summary
The authors call for long-term measurements to confirm the GHG trend.
Verbatim
e0“long-term measurements are needed to confirm this trend.”
t0“diverse crop rotation using cover crops”