Abstract
Abstract While it is established that high levels of combined N inhibit the development and function of legume root nodules, the application of low‐level “starter” doses of fertilizer‐N is sometimes recommended to improve nodulation and N 2 fixation in the long term. The amounts of combined N which are required to optimize legume symbiosis are poorly defined. Before screening a number of rhizobial isolates for effectiveness with cowpea [ Vigna unguiculata (L.) Walp.] we set out to determine what levels of fertilizer‐N are optimal for symbiosis in pot conditions. We examined the effects of fertilizer‐N applied at or soon after sowing, on nodulation, N, fixation and growth of two cultivars of cowpea and, for comparison one of soybean [ Glycine mar (L.) Merr.] in the greenhouse. Two experiments were done to examine (a) the effects of fertilizer N before flowering and (b) the effects of fertilizer‐N throughout the growth cycle and on final yield. The levels of N found to stimulate symbiosis during the pre‐flowering period were an order of magnitude higher than those previously reported. Applications of 36 and 72 mg N/plant increased nodule weights and acetylene reduction activities up to fourfold and sixfold, respectively, but trends varied with legume host and time of harvest. When 30, 90, 180, or 360 mg N/plant were applied as NH 4 NO 3 , KNO 3 , or urea, symbiotic responses again varied and no single N treatment was optimal for all three legumes. Synergistic effects of applied N on total amounts of N fixed were observed with each host with various N treatments. The strongest synergism occurred in soybean with urea at 30 mg N/plant; for every milligram of urea‐N absorbed, an additional 15 mg of N were fixed symbiotically.
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Claims 6
Claim · model-written summary
Preflowering nitrogen levels that stimulated symbiosis were an order of magnitude above earlier reports.
- Taxon
- Cowpea and Soybean
Glycine max
Vigna unguiculatat0 - Outcome
- levels of N found to stimulate symbiosise0
- Direction
- highere0
- Value
- an order of magnitudee0
- Comparator
- those previously reportede0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“The levels of N found to stimulate symbiosis during the pre‐flowering period were an order of magnitude higher than those previously reported.”
t0“Cowpea and Soybean”
Claim · model-written summary
Fertilizer nitrogen at 36 mg N/plant increased nodule weights up to fourfold.
- Taxon
- Cowpea and SoybeanGlycine maxVigna unguiculatat0
- Treatment
- 36e0
- Outcome
- nodule weightse0
- Direction
- increasede0
- Value
- fourfolde0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Applications of 36 and 72 mg N/plant increased nodule weights and acetylene reduction activities up to fourfold and sixfold, respectively”
t0“Cowpea and Soybean”
Claim · model-written summary
Fertilizer nitrogen at 72 mg N/plant increased acetylene reduction activity up to sixfold.
- Taxon
- Cowpea and SoybeanGlycine maxVigna unguiculatat0
- Treatment
- 72 mg N/plante0
- Outcome
- acetylene reduction activitiese0
- Direction
- increasede0
- Value
- sixfolde0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Applications of 36 and 72 mg N/plant increased nodule weights and acetylene reduction activities up to fourfold and sixfold, respectively”
t0“Cowpea and Soybean”
Claim · model-written summary
Symbiotic responses varied across nitrogen treatments and hosts, with no single treatment optimal for all three legumes.
- Taxon
- Cowpea and SoybeanGlycine maxVigna unguiculatat0
- Outcome
- symbiotic responses again varied and no single N treatment was optimal for all three legumese0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“symbiotic responses again varied and no single N treatment was optimal for all three legumes”
t0“Cowpea and Soybean”
Claim · model-written summary
Applied nitrogen acted synergistically on total nitrogen fixed in each host under various treatments.
- Taxon
- Cowpea and SoybeanGlycine maxVigna unguiculatat0
- Treatment
- applied Ne0
- Outcome
- total amounts of N fixede0
Not reportedComparatorDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Synergistic effects of applied N on total amounts of N fixed were observed with each host with various N treatments.”
t0“Cowpea and Soybean”
Claim · model-written summary
Soybean given urea at 30 mg N/plant had the strongest synergism, fixing an additional 15 mg N per mg urea-N absorbed.
- Taxon
- soybeanGlycine maxe0
- Treatment
- urea at 30 mg N/plante0
- Outcome
- N were fixed symbioticallye0
- Direction
- additionale0
- Value
- 15 mg of Ne0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“The strongest synergism occurred in soybean with urea at 30 mg N/plant; for every milligram of urea‐N absorbed, an additional 15 mg of N were fixed symbiotically.”
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See all 146 papers →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.