Abstract
Under the hypothesis that grain yield is limited by nitrogen (N) supply in late reproductive stages when soybean is grown in high-yielding environments, a 2-year study was conducted in order to evaluate whether N fertilization increases grain yield and N uptake, and to what extent N2 fixation is complemented when fertilizer N was applied both on surface as well as below the nodules. Four N fertilization treatments were established in the soybean main plots of each year's soybean/maize rotation in a long-term experiment. Treatments were: a non-fertilized plot (N1) and 180 kg N ha-1 applied as (i) polymer-coated controlled release urea placed 20 cm below the surface before planting (N2, late N fertilization strategy); (ii) ammonium nitrate on the surface before planting and at V6 (N3, early N fertilization strategy) and, (iii) ammonium nitrate on the surface at R5 (N4, late N fertilization strategy). All treatments were superimposed on two contrasting fertilizer management histories for maize (M1=recommended nutrient management; M2=intensive nutrient management). Grain yield in N1 averaged 4850 kg ha-1, and a 5% increase was observed in response to N fertilization. This response was accompanied by a 9% increase in N uptake. Biological N2 fixation accounted for 50% of N uptake in N1, but only 32 and 38% in N3 and N4, respectively. All N fertilization strategies succeeded in providing the additional N needed to attain the apparent maximum grain yield, but the amount of fertilizer N needed to achieve grain yield response was larger with ammonium nitrate applied on the surface N. This was because a proportion of total N derived from surface applied ammonium nitrate depressed N2 fixation. In contrast, deep placement of slow-release urea did not depress biological N2 fixation, and thus, showed the advantage of providing the additional N needed to reach grain yield potential with minimal trade-off between fixed N and fertilizer N. The greater photosynthesis response to light observed in fertilized soybean suggests that N fertilization in high-yielding soybean should simultaneously take into account management practices intended to maximize canopy light capture.
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Claims 9
Claim · model-written summary
N fertilization increased grain yield by 5% relative to the non-fertilized N1 treatment.
- Taxon
- soybean
Glycine maxt0 - Treatment
- N fertilizatione1
- Outcome
- Grain yielde1
- Direction
- increasee1
- Value
- 5%e1
- Comparator
- N1e1
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“high yielding soybean”
e1“Grain yield in N1 averaged 4850 kg ha-1, and a 5% increase was observed in response to N fertilization”
Claim · model-written summary
N fertilization increased N uptake by 9%.
- Taxon
- soybeanGlycine maxt0
- Treatment
- N fertilizatione1
- Outcome
- N uptakee2
- Direction
- increasee2
- Value
- 9%e2
- Comparator
- N1e1
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“high yielding soybean”
e1“Grain yield in N1 averaged 4850 kg ha-1, and a 5% increase was observed in response to N fertilization”
e2“This response was accompanied by a 9% increase in N uptake”
Claim · model-written summary
Ammonium nitrate applied on the surface lowered the share of N uptake from biological N2 fixation to 32 and 38%, against 50% in N1.
- Taxon
- soybeanGlycine maxt0
- Treatment
- ammonium nitrate on the surfacee4
- Outcome
- Biological N2 fixatione3
- Direction
- lowerinferrede3
- Value
- 32 and 38%e3
- Comparator
- N1e3
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“high yielding soybean”
e3“Biological N2 fixation accounted for 50% of N uptake in N1, but only 32 and 38% in N3 and N4, respectively”
e4“ammonium nitrate on the surface before planting and at V6 (N3, early N fertilization strategy)”
Claim · model-written summary
Surface applied ammonium nitrate depressed N2 fixation, because part of the total N it supplied replaced fixed N.
- Taxon
- soybeanGlycine maxt0
- Treatment
- surface applied ammonium nitratee5
- Outcome
- N2 fixatione5
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“high yielding soybean”
e5“This was because a proportion of total N derived from surface applied ammonium nitrate depressed N2 fixation”
Claim · model-written summary
Deep placement of slow-release urea did not depress biological N2 fixation, unlike surface applied ammonium nitrate.
- Taxon
- soybeanGlycine maxt0
- Treatment
- deep placement of slow-release ureae6
- Outcome
- biological N2 fixatione6
- Direction
- did not depresse6
- Comparator
- surface applied ammonium nitratee5
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“high yielding soybean”
e6“In contrast, deep placement of slow-release urea did not depress biological N2 fixation”
e5“This was because a proportion of total N derived from surface applied ammonium nitrate depressed N2 fixation”
Claim · model-written summary
More fertilizer N was needed to achieve the grain yield response with ammonium nitrate applied on the surface.
- Taxon
- soybeanGlycine maxt0
- Treatment
- ammonium nitrate applied on the surfacee7
- Outcome
- the amount of fertilizer N needed to achieve grain yield responsee7
- Direction
- largere7
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“high yielding soybean”
e7“the amount of fertilizer N needed to achieve grain yield response was larger with ammonium nitrate applied on the surface N”
Claim · model-written summary
All N fertilization strategies succeeded in providing the additional N needed to attain the apparent maximum grain yield.
- Taxon
- soybeanGlycine maxt0
- Treatment
- N fertilization strategiese0
- Outcome
- apparent maximum grain yielde0
- Direction
- succeeded ine0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“high yielding soybean”
e0“All N fertilization strategies succeeded in providing the additional N needed to attain the apparent maximum grain yield”
Claim · model-written summary
N fertilization increased the photosynthesis response to light in fertilized soybean.
- Taxon
- soybeanGlycine maxt0
- Treatment
- N fertilizatione7
- Outcome
- photosynthesis response to lighte7
- Direction
- greatere7
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“high yielding soybean”
e7“The greater photosynthesis response to light observed in fertilized soybean suggests that N fertilization in high-yielding soybean should simultaneously take into account management practices intended to maximize canopy light capture”
Claim · model-written summary
N fertilization in high-yielding soybean should take into account management practices intended to maximize canopy light capture.
- Taxon
- soybeanGlycine maxt0
- Outcome
- management practices intended to maximize canopy light capturee7
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“high yielding soybean”
e7“The greater photosynthesis response to light observed in fertilized soybean suggests that N fertilization in high-yielding soybean should simultaneously take into account management practices intended to maximize canopy light capture”
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