Abstract
Most soil nitrous oxide (N2O) emissions from rain-fed grain sorghum grown on sub-tropical Vertosols in north-west New South Wales, Australia, occur between fertiliser nitrogen (N) application at sowing and booting growth stage. At three experiments, we investigated the potential for deferring some (split-N) or all (delayed) fertiliser N until booting to mitigate N2O produced without compromising optimum crop yields. N products included urea, 3,4-dimethyl pyrazole phosphate (DMPP)-urea, polymer-coated urea (PCU) and N-(n-butyl)thiophosphoric triamide (NBPT)-urea. For a fourth experiment, the N fertiliser rate was varied according to pre-sowing soil mineral N stocks left by different previous crops. All experiments incorporated 15N mini-plots to determine whether delayed or split-N affected crop N uptake or residual soil N. Compared to urea applied at-sowing, delayed applications of urea, DMPP-urea or NBPT-urea at booting reduced the N2O emission factor (EF, percentage of applied N emitted) by 67–81%. Crop N uptake, grain yield and protein tended to be lower with delayed N than N at-sowing due to dry mid-season conditions. Much of the unused N remained in the soil at harvest. Split-N (33% sowing : 67% booting) using urea, reduced EF by 59% compared to at-sowing urea, but maintained crop N uptake, grain yield and protein. Using DMPP-urea or PCU for the at-sowing portion of the split reduced EF by 84–86%. Grain yield was maintained using PCU, but was lower with DMPP-urea, which had more N in vegetative biomass. Using NBPT-urea for the in-crop portion of the split did not affect N2O emissions or crop productivity. Nitrogen budgeting to account for high pre-sowing soil mineral N nullified urea-induced N2O emissions. An N-budgeted, split-N strategy using urea offers the best balance between N2O mitigation, grain productivity and provision of a soil mineral N buffer against dry mid-season conditions. Split-N using DMPP-urea or PCU further enhanced N2O mitigation but there was no yield response to justify the extra expense.
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Claims 18
Claim · model-written summary
Delayed urea reduced the N2O emission factor by 67–81% compared with urea at sowing.
- Treatment
- delayed applications of ureae0
- Outcome
- N2O emission factore0
- Direction
- reducede0
- Value
- 67–81%e0
- Comparator
- urea applied at-sowinge0
Not reportedTaxon
Verbatim
e0“Compared to urea applied at-sowing, delayed applications of urea, DMPP-urea or NBPT-urea at booting reduced the N2O emission factor (EF, percentage of applied N emitted) by 67–81%.”
Claim · model-written summary
Delayed DMPP-urea reduced the N2O emission factor by 67–81% compared with urea at sowing.
- Treatment
- DMPP-ureae0
- Outcome
- N2O emission factore0
- Direction
- reducede0
- Value
- 67–81%e0
- Qualifier
- at bootinge0
- Comparator
- urea applied at-sowinge0
Not reportedTaxon
Verbatim
e0“Compared to urea applied at-sowing, delayed applications of urea, DMPP-urea or NBPT-urea at booting reduced the N2O emission factor (EF, percentage of applied N emitted) by 67–81%.”
Claim · model-written summary
Delayed NBPT-urea reduced the N2O emission factor by 67–81% compared with urea at sowing.
- Treatment
- NBPT-ureae0
- Outcome
- N2O emission factore0
- Direction
- reducede0
- Value
- 67–81%e0
- Qualifier
- at bootinge0
- Comparator
- urea applied at-sowinge0
Not reportedTaxon
Verbatim
e0“Compared to urea applied at-sowing, delayed applications of urea, DMPP-urea or NBPT-urea at booting reduced the N2O emission factor (EF, percentage of applied N emitted) by 67–81%.”
Claim · model-written summary
Delayed nitrogen tended to lower crop nitrogen uptake, grain yield and protein under dry mid-season conditions.
- Taxon
- grain sorghum
Sorghum bicolort0 - Treatment
- delayed Ne0
- Outcome
- Crop N uptake, grain yield and proteine0
- Direction
- lowere0
- Qualifier
- tended to be lower with delayed N than N at-sowing due to dry mid-season conditionse0
- Comparator
- N at-sowinge0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Crop N uptake, grain yield and protein tended to be lower with delayed N than N at-sowing due to dry mid-season conditions.”
t0“grain sorghum”
Claim · model-written summary
Much unused nitrogen remained in soil at harvest.
Not reportedTaxon
Verbatim
e0“Much of the unused N remained in the soil at harvest.”
Claim · model-written summary
Split urea reduced emission factor by 59% compared with at-sowing urea.
- Treatment
- Split-N (33% sowing : 67% booting) using ureae0
- Outcome
- EFe0
- Direction
- reducede0
- Value
- 59%e0
- Comparator
- at-sowing ureae0
Not reportedTaxon
Verbatim
e0“Split-N (33% sowing : 67% booting) using urea, reduced EF by 59% compared to at-sowing urea, but maintained crop N uptake, grain yield and protein.”
Claim · model-written summary
Split urea maintained crop nitrogen uptake, grain yield and protein.
- Taxon
- grain sorghumSorghum bicolort0
- Treatment
- Split-N (33% sowing : 67% booting) using ureae0
- Outcome
- crop N uptake, grain yield and proteine0
- Direction
- maintainede0
- Comparator
- at-sowing ureae0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Split-N (33% sowing : 67% booting) using urea, reduced EF by 59% compared to at-sowing urea, but maintained crop N uptake, grain yield and protein.”
t0“grain sorghum”
Claim · model-written summary
DMPP-urea in the at-sowing split portion reduced emission factor by 84–86%.
- Treatment
- DMPP-ureae0
- Outcome
- EFe0
- Direction
- reducede0
- Value
- 84–86%e0
- Qualifier
- for the at-sowing portion of the splite0
Not reportedTaxonComparator
Verbatim
e0“Using DMPP-urea or PCU for the at-sowing portion of the split reduced EF by 84–86%.”
Claim · model-written summary
PCU in the at-sowing split portion reduced emission factor by 84–86%.
- Treatment
- PCUe0
- Outcome
- EFe0
- Direction
- reducede0
- Value
- 84–86%e0
- Qualifier
- for the at-sowing portion of the splite0
Not reportedTaxonComparator
Verbatim
e0“Using DMPP-urea or PCU for the at-sowing portion of the split reduced EF by 84–86%.”
Claim · model-written summary
PCU maintained grain yield.
- Taxon
- grain sorghumSorghum bicolort0
- Treatment
- PCUe0
- Outcome
- Grain yielde0
- Direction
- maintainede0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Grain yield was maintained using PCU, but was lower with DMPP-urea, which had more N in vegetative biomass.”
t0“grain sorghum”
Claim · model-written summary
DMPP-urea lowered grain yield.
- Taxon
- grain sorghumSorghum bicolort0
- Treatment
- DMPP-ureae0
- Outcome
- Grain yielde0
- Direction
- lowere0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Grain yield was maintained using PCU, but was lower with DMPP-urea, which had more N in vegetative biomass.”
t0“grain sorghum”
Claim · model-written summary
DMPP-urea had more nitrogen in vegetative biomass.
- Taxon
- grain sorghumSorghum bicolort0
- Treatment
- DMPP-ureae0
- Outcome
- N in vegetative biomasse0
- Direction
- moree0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Grain yield was maintained using PCU, but was lower with DMPP-urea, which had more N in vegetative biomass.”
t0“grain sorghum”
Claim · model-written summary
NBPT-urea in the in-crop split portion did not affect N2O emissions.
- Treatment
- NBPT-ureae0
- Outcome
- N2O emissionse0
- Direction
- did not affecte0
- Qualifier
- for the in-crop portion of the splite0
Not reportedTaxonComparator
Verbatim
e0“Using NBPT-urea for the in-crop portion of the split did not affect N2O emissions or crop productivity.”
Claim · model-written summary
NBPT-urea in the in-crop split portion did not affect crop productivity.
- Taxon
- grain sorghumSorghum bicolort0
- Treatment
- NBPT-ureae0
- Outcome
- crop productivitye0
- Direction
- did not affecte0
- Qualifier
- for the in-crop portion of the splite0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Using NBPT-urea for the in-crop portion of the split did not affect N2O emissions or crop productivity.”
t0“grain sorghum”
Claim · model-written summary
Nitrogen budgeting for high pre-sowing soil nitrogen nullified urea-induced N2O emissions.
- Treatment
- Nitrogen budgeting to account for high pre-sowing soil mineral Ne0
- Outcome
- urea-induced N2O emissionse0
- Direction
- nullifiede0
Not reportedTaxonComparator
Verbatim
e0“Nitrogen budgeting to account for high pre-sowing soil mineral N nullified urea-induced N2O emissions.”
Claim · model-written summary
The authors recommend nitrogen-budgeted split urea to balance emission mitigation, productivity and soil nitrogen buffering.
- Taxon
- grain sorghumSorghum bicolort0
- Outcome
- An N-budgeted, split-N strategy using ureae0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“An N-budgeted, split-N strategy using urea offers the best balance between N2O mitigation, grain productivity and provision of a soil mineral N buffer against dry mid-season conditions.”
t0“grain sorghum”
Claim · model-written summary
Split DMPP-urea further enhanced emission mitigation without a yield response justifying its additional expense.
- Taxon
- grain sorghumSorghum bicolort0
- Treatment
- DMPP-ureae0
- Outcome
- yield responsee0
- Direction
- no yield responsee0
- Qualifier
- to justify the extra expensee0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Split-N using DMPP-urea or PCU further enhanced N2O mitigation but there was no yield response to justify the extra expense.”
t0“grain sorghum”
Claim · model-written summary
Split PCU further enhanced emission mitigation without a yield response justifying its additional expense.
- Taxon
- grain sorghumSorghum bicolort0
- Treatment
- PCUe0
- Outcome
- yield responsee0
- Direction
- no yield responsee0
- Qualifier
- to justify the extra expensee0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Split-N using DMPP-urea or PCU further enhanced N2O mitigation but there was no yield response to justify the extra expense.”
t0“grain sorghum”
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Claims are grouped by organism, treatment and what was measured or targeted. A paper counts as positive when any of its claims in the group is positive.