Abstract
Soil in which nodulated legumes are growing often contains more nitrate nitrogen (N) than soil in which unnodulated legumes or non-legumes are growing. There is conjecture, however, as to whether the extra or ‘spared’ N is due to reduced use of soil N by the legume or to net mineralisation of legume root and nodular N. We report results of a field experiment to quantify and compare, at different levels of soil-N supply, N2 fixation, and soil-N use by chickpea ( Cicer arietinum ) and fababean ( Vicia faba ). Wheat ( Triticum aestivum ) was included as a non-N2-fixing control. Plants of the 3 species were grown on a low-nitrate Vertosol with fertiliser N rates of 0, 50, and 100 kg/ha (0N, 50N, and 100N), applied 6 weeks before sowing. Samples were collected at sowing and at 64, 100, 135, and 162 days after sowing (DAS) for analysis of soil nitrate, root, and grain dry matter (DM) and N and shoot DM, N, and 15N. The latter was used to estimate the percentage (%Ndfa) and total N fixed by the 2 legumes. Soil nitrate levels to a depth of 1.8 m at sowing were 11–17 kg N/ha (0N), 41–55 kg N/ha (50N), and 71–86 kg N/ha (100N). Grain yields of the 2 legumes were unaffected by soil-N supply (fertiliser N treatment), being 2.0–2.4 t/ha for chickpea and 3.7–4.6 t/ha for fababean. Wheat grain yields varied from 1.6 t/ha (0N) to 4.8 t/ha (100N). Fababean fixed more N than chickpea. Values (total plant including roots) were 209–275 kg/ha for fababean and 146–214 kg/ha for chickpea. Corresponding %Ndfa values were 69–88% (fababean) and 64–85% (chickpea). Early in crop growth, when soil N supply was high in the 100N treatment, fababean maintained a higher dependence on N2 fixation than chickpea (Ndfa of 45% v . 12%), fixed greater amounts of N (57 v . 16 kg/ha), and used substantially less soil N (69 v . 118 kg/ha). In this situation, soil N sparing was observed, with soil nitrate levels significantly higher in the fababean plots ( P < 0.05) than under chickpea or wheat. At the end of growth season, however, there were no crop effects on soil nitrate levels. Soil N balances, which combined crop N fixed as inputs and grain N as outputs, were positive for the legumes, with ranges 80–135 kg N/ha for chickpea and 79–157 kg N/ha for fababean, and negative for wheat (–20 to –66 kg N/ha). We concluded that under the starting soil nitrate levels in this experiment, levels typical of many cropping soils in the region, high-biomass fababean and chickpea crops will not spare significant amounts of soil N. In situations of higher soil nitrate and/or smaller biomass crops with less N demand, nitrate sparing may occur, particularly with fababean.
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Claims 16
Claim · model-written summary
Chickpea grain yield was unaffected by fertilizer nitrogen supply and ranged from 2.0–2.4 t/ha.
- Taxon
- chickpea
Cicer arietinume0 - Treatment
- fertiliser N treatmente0
- Outcome
- Grain yieldse0
- Direction
- unaffectede0
- Value
- 2.0–2.4 t/hae0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Grain yields of the 2 legumes were unaffected by soil-N supply (fertiliser N treatment), being 2.0–2.4 t/ha for chickpea”
Claim · model-written summary
Fababean grain yield was unaffected by fertilizer nitrogen supply and ranged from 3.7–4.6 t/ha.
- Taxon
- fababean
Vicia fabae0 - Treatment
- fertiliser N treatmente0
- Outcome
- Grain yieldse0
- Direction
- unaffectede0
- Value
- 3.7–4.6 t/hae0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Grain yields of the 2 legumes were unaffected by soil-N supply (fertiliser N treatment), being 2.0–2.4 t/ha for chickpea and 3.7–4.6 t/ha for fababean”
Claim · model-written summary
Wheat grain yield rose from 1.6 t/ha at 0N to 4.8 t/ha at 100N.
- Taxon
- Wheat
Triticum aestivume0 - Treatment
- 100Ne0
- Outcome
- grain yieldse0
- Direction
- variede0
- Value
- 4.8 t/hae0
- Qualifier
- 1.6 t/hae0
- Comparator
- 0Ne0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Wheat grain yields varied from 1.6 t/ha (0N) to 4.8 t/ha (100N)”
Claim · model-written summary
Fababean fixed more nitrogen than chickpea, with ranges of 209–275 and 146–214 kg/ha, respectively.
- Taxon
- fababeanVicia fabae0
- Outcome
- fixed more Ne0
- Value
- 209–275 kg/hae0
- Qualifier
- 146–214 kg/hae0
- Comparator
- chickpeae0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Fababean fixed more N than chickpea. Values (total plant including roots) were 209–275 kg/ha for fababean and 146–214 kg/ha for chickpea”
Claim · model-written summary
Fababean had 69–88% nitrogen derived from fixation.
- Taxon
- fababeanVicia fabae0
- Outcome
- %Ndfae0
- Value
- 69–88%e0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Corresponding %Ndfa values were 69–88% (fababean)”
Claim · model-written summary
Chickpea had 64–85% nitrogen derived from fixation.
- Taxon
- chickpeaCicer arietinume0
- Value
- 64–85%e0
Not reportedOutcome
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“64–85% (chickpea)”
Claim · model-written summary
Under high early soil nitrogen, fababean depended more on fixation than chickpea, 45% versus 12%.
- Taxon
- fababeanVicia fabae0
- Outcome
- dependence on N2 fixatione0
- Value
- 45%e0
- Qualifier
- 12%e0
- Comparator
- chickpeae0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Early in crop growth, when soil N supply was high in the 100N treatment, fababean maintained a higher dependence on N2 fixation than chickpea (Ndfa of 45% v . 12%)”
Claim · model-written summary
Under high early soil nitrogen, fababean fixed more nitrogen than chickpea, 57 versus 16 kg/ha.
Not reportedTaxon
Verbatim
e0“fixed greater amounts of N (57 v . 16 kg/ha)”
Claim · model-written summary
Under high early soil nitrogen, fababean used less soil nitrogen than chickpea, 69 versus 118 kg/ha.
Not reportedTaxon
Verbatim
e0“used substantially less soil N (69 v . 118 kg/ha)”
Claim · model-written summary
Early soil nitrate was significantly higher under fababean than chickpea or wheat.
- Taxon
- fababeanVicia fabae0
- Outcome
- soil nitrate levelse0
- Direction
- highere0
- Comparator
- chickpea or wheate0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“soil nitrate levels significantly higher in the fababean plots ( P < 0.05) than under chickpea or wheat”
Claim · model-written summary
At season end, crops did not differ in soil nitrate.
Not reportedTaxon
Verbatim
e0“At the end of growth season, however, there were no crop effects on soil nitrate levels”
Claim · model-written summary
The chickpea soil nitrogen balance was positive, 80–135 kg N/ha.
- Taxon
- chickpeaCicer arietinume0
- Outcome
- Soil N balancese0
- Direction
- positivee0
- Value
- 80–135 kg N/hae0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Soil N balances, which combined crop N fixed as inputs and grain N as outputs, were positive for the legumes, with ranges 80–135 kg N/ha for chickpea”
Claim · model-written summary
The fababean soil nitrogen balance was positive, 79–157 kg N/ha.
- Taxon
- fababeanVicia fabae0
- Value
- 79–157 kg N/hae0
Not reportedOutcome
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“79–157 kg N/ha for fababean”
Claim · model-written summary
The wheat soil nitrogen balance was negative, –20 to –66 kg N/ha.
- Taxon
- wheatTriticum aestivume0
- Direction
- negativee0
- Value
- –20 to –66 kg N/hae0
Not reportedOutcome
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“negative for wheat (–20 to –66 kg N/ha)”
Claim · model-written summary
The authors conclude that high biomass chickpea and fababean crops will not spare significant soil nitrogen at the studied initial nitrate levels.
- Taxon
- fababean and chickpeaCicer arietinumVicia fabae0
- Outcome
- will not spare significant amounts of soil Ne0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“under the starting soil nitrate levels in this experiment, levels typical of many cropping soils in the region, high-biomass fababean and chickpea crops will not spare significant amounts of soil N”
Claim · model-written summary
The authors suggest nitrate sparing may occur at higher soil nitrate or with smaller crops, especially fababean.
- Taxon
- fababeanVicia fabae0
- Outcome
- nitrate sparing may occure0
- Qualifier
- higher soil nitrate and/or smaller biomass crops with less N demande0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“In situations of higher soil nitrate and/or smaller biomass crops with less N demand, nitrate sparing may occur, particularly with fababean”
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