Abstract
Biological nitrogen fixation (BNF) by legume crops was estimated in a Mediterranean environment at ICARDA in northern Syria for 3 consecutive seasons beginning in 1991-92. Using the classical isotope dilution technique (NID), estimates ranged from 32 to 82 kg N/ha for chickpea and from 18 to 82 kg N/ha for lentil. In comparison the simple N-difference method gave lower, sometimes negative, estimates for BNF by both crops in the latter 2 seasons but a higher estimate for chickpea in the first year. Discrepancies in the estimates from N-difference were correlated with differences in the amount of soil N taken up by the legume and the non-fixing wheat reference crop. Since soil N uptake by lentil in the first year was similar to wheat, the estimates of BNF from the 2 methods for that season were similar. The indirect effects of an interaction of added N fertiliser on N derived from the soil and thus on N uptake and estimated BNF are discussed in relation to the use of the isotope dilution method with A-value modification (NAV). Despite some significant differences in A-value for soils receiving different amounts of fertiliser it is demonstrated that the A-value method used in this study, with fertiliser rates of 10 kg N/ha to the legume and 30 kg N/ha to the non-legume, resulted in BNF estimates for lentil similar to those obtained using classical isotope dilution. However, this was not the case for chickpea where a direct inhibitory effect of fertiliser N at 30 kg N/ha resulted in lower estimates of BNF from NID than NAV. Since the reference crops derived as much as 90% of their N from the soil, it is recommended that future BNF studies using isotope dilution techniques for lentil and chickpea crops at ICARDA use a fertiliser rate lower than that used in this study. An isotope dilution method utilising a slow-release source of 15N or the natural abundance technique for estimating BNF are suggested as potentially useful alternatives. The need for a basic understanding of the soil N dynamics pertinent to each site as a prerequisite for choosing an appropriate method for estimating BNF is highlighted.
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Claims 15
Claim · model-written summary
Isotope dilution estimated chickpea fixation at 32–82 kg N/ha.
- Taxon
- chickpea
Cicer arietinume0 - Outcome
- estimatese0
- Value
- 32 to 82 kg N/hae0
- Qualifier
- classical isotope dilution technique (NID)e1
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“estimates ranged from 32 to 82 kg N/ha for chickpea”
e1“Biological nitrogen fixation (BNF) by legume crops was estimated in a Mediterranean environment at ICARDA in northern Syria for 3 consecutive seasons beginning in 1991-92. Using the classical isotope dilution technique (NID), estimates ranged from 32 to 82 kg N/ha for chickpea and from 18 to 82 kg N/ha for lentil.”
Claim · model-written summary
Isotope dilution estimated lentil fixation at 18–82 kg N/ha.
- Taxon
- lentil
Lens culinarise0 - Outcome
- Biological nitrogen fixation (BNF)e1
- Value
- 18 to 82 kg N/hae0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“from 18 to 82 kg N/ha for lentil”
e1“Biological nitrogen fixation (BNF) by legume crops was estimated in a Mediterranean environment at ICARDA in northern Syria for 3 consecutive seasons beginning in 1991-92. Using the classical isotope dilution technique (NID), estimates ranged from 32 to 82 kg N/ha for chickpea and from 18 to 82 kg N/ha for lentil.”
Claim · model-written summary
N difference yielded lower and sometimes negative fixation estimates for both crops in the last two seasons.
Verbatim
e0“the simple N-difference method gave lower, sometimes negative, estimates for BNF by both crops in the latter 2 seasons”
e1“Biological nitrogen fixation (BNF) by legume crops was estimated in a Mediterranean environment at ICARDA in northern Syria for 3 consecutive seasons beginning in 1991-92. Using the classical isotope dilution technique (NID), estimates ranged from 32 to 82 kg N/ha for chickpea and from 18 to 82 kg N/ha for lentil.”
Claim · model-written summary
N difference yielded a higher chickpea estimate in the first year.
- Taxon
- chickpeaCicer arietinume0
- Outcome
- estimatee0
- Direction
- highere0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“a higher estimate for chickpea in the first year”
Claim · model-written summary
N difference discrepancies correlated with legume versus wheat soil nitrogen uptake differences.
- Taxon
- legumee0
- Compound
- soil Ne0
- Outcome
- Discrepancies in the estimates from N-differencee0
- Comparator
- non-fixing wheat reference crope0
Not reportedDirection
Verbatim
e0“Discrepancies in the estimates from N-difference were correlated with differences in the amount of soil N taken up by the legume and the non-fixing wheat reference crop”
Claim · model-written summary
Lentil and wheat had similar soil nitrogen uptake in the first year.
- Taxon
- lentilLens culinarise0
- Outcome
- soil N uptakee0
- Direction
- similare0
- Comparator
- wheate0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“soil N uptake by lentil in the first year was similar to wheat”
Claim · model-written summary
The two methods yielded similar first-year lentil fixation estimates.
- Taxon
- lentilLens culinarise1
- Outcome
- estimates of BNFe0
- Direction
- similare0
- Comparator
- 2 methodse0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“the estimates of BNF from the 2 methods for that season were similar”
e1“Biological nitrogen fixation (BNF) by legume crops was estimated in a Mediterranean environment at ICARDA in northern Syria for 3 consecutive seasons beginning in 1991-92. Using the classical isotope dilution technique (NID), estimates ranged from 32 to 82 kg N/ha for chickpea and from 18 to 82 kg N/ha for lentil.”
Claim · model-written summary
Soil A-values differed significantly across fertilizer amounts.
Not reportedTaxon
Verbatim
e0“some significant differences in A-value for soils receiving different amounts of fertiliser”
Claim · model-written summary
A-value modification yielded lentil fixation estimates similar to classical isotope dilution.
- Taxon
- lentilLens culinarise0
- Treatment
- fertiliser rates of 10 kg N/ha to the legume and 30 kg N/ha to the non-legumee0
- Outcome
- BNF estimatese0
- Direction
- similare0
- Comparator
- classical isotope dilutione0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“the A-value method used in this study, with fertiliser rates of 10 kg N/ha to the legume and 30 kg N/ha to the non-legume, resulted in BNF estimates for lentil similar to those obtained using classical isotope dilution”
Claim · model-written summary
At 30 kg N/ha, fertilizer inhibited chickpea fixation and gave lower NID estimates than NAV.
- Taxon
- chickpeaCicer arietinume1
- Treatment
- fertiliser N at 30 kg N/hae0
- Outcome
- estimates of BNF from NIDe0
- Direction
- lowere0
- Comparator
- NAVe0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“a direct inhibitory effect of fertiliser N at 30 kg N/ha resulted in lower estimates of BNF from NID than NAV”
e1“Biological nitrogen fixation (BNF) by legume crops was estimated in a Mediterranean environment at ICARDA in northern Syria for 3 consecutive seasons beginning in 1991-92. Using the classical isotope dilution technique (NID), estimates ranged from 32 to 82 kg N/ha for chickpea and from 18 to 82 kg N/ha for lentil.”
Claim · model-written summary
Reference crops derived as much as 90% of nitrogen from soil.
- Taxon
- wheat
Triticum aestivume1 - Outcome
- N from the soile0
- Value
- 90%e0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“the reference crops derived as much as 90% of their N from the soil”
e1“Discrepancies in the estimates from N-difference were correlated with differences in the amount of soil N taken up by the legume and the non-fixing wheat reference crop.”
Claim · model-written summary
Authors recommend lower fertilizer rates for isotope dilution studies of chickpea and lentil at ICARDA.
- Taxon
- lentil and chickpeaCicer arietinumLens culinarise0
- Outcome
- use a fertiliser rate lower than that used in this studye0
- Setting
- ICARDAe0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“future BNF studies using isotope dilution techniques for lentil and chickpea crops at ICARDA use a fertiliser rate lower than that used in this study”
Claim · model-written summary
Authors suggest slow-release 15N isotope dilution as an alternative for fixation estimation.
Verbatim
e0“An isotope dilution method utilising a slow-release source of 15N or the natural abundance technique for estimating BNF are suggested as potentially useful alternatives”
e1“Biological nitrogen fixation (BNF) by legume crops was estimated in a Mediterranean environment at ICARDA in northern Syria for 3 consecutive seasons beginning in 1991-92. Using the classical isotope dilution technique (NID), estimates ranged from 32 to 82 kg N/ha for chickpea and from 18 to 82 kg N/ha for lentil.”
Claim · model-written summary
Authors suggest natural abundance as another alternative for fixation estimation.
Verbatim
e0“An isotope dilution method utilising a slow-release source of 15N or the natural abundance technique for estimating BNF are suggested as potentially useful alternatives”
e1“Biological nitrogen fixation (BNF) by legume crops was estimated in a Mediterranean environment at ICARDA in northern Syria for 3 consecutive seasons beginning in 1991-92. Using the classical isotope dilution technique (NID), estimates ranged from 32 to 82 kg N/ha for chickpea and from 18 to 82 kg N/ha for lentil.”
Claim · model-written summary
Authors highlight site soil nitrogen dynamics as necessary for selecting a fixation method.
Verbatim
e0“The need for a basic understanding of the soil N dynamics pertinent to each site as a prerequisite for choosing an appropriate method for estimating BNF is highlighted”
e1“Biological nitrogen fixation (BNF) by legume crops was estimated in a Mediterranean environment at ICARDA in northern Syria for 3 consecutive seasons beginning in 1991-92. Using the classical isotope dilution technique (NID), estimates ranged from 32 to 82 kg N/ha for chickpea and from 18 to 82 kg N/ha for lentil.”
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