Abstract
Functions quantifying relationships between N2 fixation by legumes and other factors would be useful to farmers in the management of legumes and nitrogen in their production systems. The 2 most critical factors regulating N2 fixation are legume yield and soil nitrate and both should be included as independent variables in the functions. Data from 9 experiments in northern New South Wales on soil nitrate at sowing, yields of shoot and grain dry matter (DM) and N of chickpea, and d15N of shoots of chickpea and non N2-fixing reference crops (wheat, barley, and uninoculated chickpea) were used to determine the percentage of chickpea N derived from N2 fixation ( P fix), total N2 fixed, and N balance (fixed N2 minus grain N). Data were then subjected to simple and multivariate regression analyses with Pfix and total N2 fixed as the dependent variables and soil nitrate, shoot N, and grain yield as the independent variables. Simple regression coefficients (r2) for P fix were 0·26 with shoot N as the independent variable, 0·59 with soil nitrate, and 0·62 with grain yield. Coefficient values were increased in the 2-factor (multiple) regressions to 0·74 ( P <0·001) for soil nitrate plus shoot N, and 0·82 ( P < 0·001) for soil nitrate plus grain yield. For total N2 fixed, the regression coefficient was lower at 0·68 ( P < 0·001), using soil nitrate plus grain yield. We tested the functions against an independent data set with best prediction of P fix involving the nitrate and grain yield equation ( r 2 = 0·83; P < 0·001). Total N2 fixed was not well predicted. We concluded that further development of such functions is warranted to refine both accuracy and precision for chickpea and to extend the approach to other species.
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Claims 9
Claim · model-written summary
Shoot N alone explained 0·26 of variation in chickpea P fix.
- Taxon
- chickpea
Cicer arietinume1 - Organ / stage
- shoote0
- Outcome
- P fixe0
- Value
- 0·26e0
Not reportedDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Simple regression coefficients (r2) for P fix were 0·26 with shoot N as the independent variable”
e1“N of chickpea”
Claim · model-written summary
Soil nitrate alone explained 0·59 of variation in chickpea P fix.
- Taxon
- chickpeaCicer arietinume1
- Outcome
- P fixe0
- Value
- 0·59e0
- Setting
- soil nitratee0
Not reportedDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Simple regression coefficients (r2) for P fix were 0·26 with shoot N as the independent variable, 0·59 with soil nitrate”
e1“N of chickpea”
Claim · model-written summary
Grain yield alone explained 0·62 of variation in chickpea P fix.
- Taxon
- chickpeaCicer arietinume1
- Organ / stage
- graine0
- Outcome
- P fixe0
- Value
- 0·62e0
Not reportedDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Simple regression coefficients (r2) for P fix were 0·26 with shoot N as the independent variable, 0·59 with soil nitrate, and 0·62 with grain yield”
e1“N of chickpea”
Claim · model-written summary
Soil nitrate plus shoot N gave a chickpea P fix multiple-regression coefficient of 0·74.
- Taxon
- chickpeaCicer arietinume1
- Outcome
- 2-factor (multiple) regressionse0
- Direction
- increasede0
- Value
- 0·74e0
- Qualifier
- P <0·001e0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Coefficient values were increased in the 2-factor (multiple) regressions to 0·74 ( P <0·001) for soil nitrate plus shoot N”
e1“N of chickpea”
Claim · model-written summary
Soil nitrate plus grain yield gave a chickpea P fix multiple-regression coefficient of 0·82.
- Taxon
- chickpeaCicer arietinume1
- Outcome
- 2-factor (multiple) regressionse0
- Direction
- increasede0
- Value
- 0·82e0
- Qualifier
- P < 0·001e0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Coefficient values were increased in the 2-factor (multiple) regressions to 0·74 ( P <0·001) for soil nitrate plus shoot N, and 0·82 ( P < 0·001) for soil nitrate plus grain yield”
e1“N of chickpea”
Claim · model-written summary
For total N2 fixed, the soil nitrate and grain-yield regression coefficient was lower at 0·68.
- Taxon
- chickpeaCicer arietinume1
- Outcome
- total N2 fixede0
- Direction
- lowere0
- Value
- 0·68e0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“For total N2 fixed, the regression coefficient was lower at 0·68 ( P < 0·001), using soil nitrate plus grain yield.”
e1“N of chickpea”
Claim · model-written summary
The nitrate and grain-yield equation best predicted chickpea P fix in independent data with r squared 0·83.
- Taxon
- chickpeaCicer arietinume1
- Outcome
- prediction of P fixe0
- Direction
- beste0
- Value
- 0·83e0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“best prediction of P fix involving the nitrate and grain yield equation ( r 2 = 0·83; P < 0·001)”
e1“N of chickpea”
Claim · model-written summary
The functions predicted total chickpea N2 fixed poorly.
- Taxon
- chickpeaCicer arietinume1
- Outcome
- Total N2 fixed was not well predictede0
Not reportedComparatorValue
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Total N2 fixed was not well predicted.”
e1“N of chickpea”
Claim · model-written summary
The authors recommend further development of chickpea N2 fixation functions to improve accuracy and precision and extend them to other species.
- Taxon
- chickpeaCicer arietinume0
- Outcome
- further development of such functions is warrantede0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“further development of such functions is warranted to refine both accuracy and precision for chickpea and to extend the approach to other species”