Abstract
Several new and existing short-term forage legumes could be used to provide nitrogen (N) inputs for grain crops in subtropical farming systems. The fixed-N inputs from summer-growing forage legumes lablab (Lablab purpureus), burgundy bean (Macroptilium bracteatum) and lucerne (Medicago sativa) and winter-growing legume species snail medic (Medicago scutellata), sulla (Hedysarum coronarium) and purple vetch (Vicia benghalensis) were compared over several growing seasons at four locations in southern Queensland, Australia. Available soil mineral N and grain yield of a following cereal crop were compared among summer-growing legumes and forage sorghum (Sorghum spp. hybrid) and among winter-growing legumes and forage oats (Avena sativa). In the first year at all sites, legumes utilised the high initial soil mineral N, with <30% of the legume N estimated to have been derived from atmospheric N2 (%Ndfa) and legume-fixed N <30 kg/ha. In subsequent years, once soil mineral N had been depleted, %Ndfa increased to 50–70% in the summer-growing legumes and to 60–80% in winter-growing legumes. However, because forage shoot N was removed, rarely did fixed N provide a positive N balance. Both lablab and burgundy bean fixed up to 150 kg N/ha, which was more than lucerne in all seasons. Prior to sowing cereal grain crops, soil nitrate was 30–50 kg/ha higher after summer legumes than after forage sorghum. At one site, lablab and lucerne increased the growth and yield of a subsequent grain sorghum crop by 1.4 t/ha compared with growth after forage sorghum or burgundy bean. Of the winter-growing legumes, sulla had the highest total N2 fixation (up to 150 kg N/ha.year) and inputs of fixed N (up to 75 kg N/ha), and resulted in the highest concentrations of soil N (80–100 kg N/ha more than oats) before sowing of the following crop. Wheat protein was increased after winter legumes, but there was no observed yield benefit for wheat or grain sorghum crops. New forage legume options, lablab, burgundy bean and sulla, showed potential to increase N supply in crop rotations in subtropical farming systems, contributing significant fixed N (75–150 kg/ha) and increasing available soil N for subsequent crops compared to non-legume forage crops. However, high soil mineral N (>50 kg N/ha) greatly reduced N2 fixation by forage legumes, and significant N2 fixation only occurred once legume shoot N uptake exceeded soil mineral N at the start of the growing season. Further work is required to explore the impact of different management strategies, such as livestock grazing rather than harvesting for hay, on the long-term implications for nutrient supply for subsequent crops.
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Claims 18
Claim · model-written summary
In the first year legumes derived less than 30% of nitrogen from atmospheric N2.
Verbatim
e0“In the first year at all sites, legumes utilised the high initial soil mineral N, with <30% of the legume N estimated to have been derived from atmospheric N2 (%Ndfa) and legume-fixed N <30 kg/ha”
Claim · model-written summary
First-year legume fixed nitrogen was below 30 kg/ha.
Verbatim
e0“legume-fixed N <30 kg/ha”
Claim · model-written summary
Summer legumes subsequently derived 50–70% of N from atmospheric N2.
Verbatim
e0“%Ndfa increased to 50–70% in the summer-growing legumes”
Claim · model-written summary
Winter legumes subsequently derived 60–80% of N from atmospheric N2.
Verbatim
e0“%Ndfa increased to 50–70% in the summer-growing legumes and to 60–80% in winter-growing legumes”
Claim · model-written summary
Removal of forage shoots rarely left a positive fixed-N balance.
Not reportedDirection
Verbatim
e0“because forage shoot N was removed, rarely did fixed N provide a positive N balance”
Claim · model-written summary
Lablab fixed up to 150 kg N/ha, more than lucerne.
LablabOrganisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Both lablab and burgundy bean fixed up to 150 kg N/ha, which was more than lucerne in all seasons”
Claim · model-written summary
Burgundy bean fixed up to 150 kg N/ha, more than lucerne.
Verbatim
e0“Both lablab and burgundy bean fixed up to 150 kg N/ha, which was more than lucerne in all seasons”
Claim · model-written summary
Soil nitrate before cereal sowing was 30–50 kg/ha higher after summer legumes than forage sorghum.
Verbatim
e0“soil nitrate was 30–50 kg/ha higher after summer legumes than after forage sorghum”
Claim · model-written summary
At one site lablab increased subsequent grain sorghum growth and yield by 1.4 t/ha.
- Taxon
- grain sorghum
Sorghum bicolore0 - Treatment
- lablabe0
- Outcome
- growth and yielde0
- Direction
- increasede0
- Value
- 1.4 t/hae0
- Comparator
- forage sorghum or burgundy beane0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“At one site, lablab and lucerne increased the growth and yield of a subsequent grain sorghum crop by 1.4 t/ha compared with growth after forage sorghum or burgundy bean”
Claim · model-written summary
At one site lucerne increased subsequent grain sorghum growth and yield by 1.4 t/ha.
- Taxon
- grain sorghumSorghum bicolore0
- Treatment
- lucernee0
- Outcome
- growth and yielde0
- Direction
- increasede0
- Value
- 1.4 t/hae0
- Comparator
- forage sorghum or burgundy beane0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“At one site, lablab and lucerne increased the growth and yield of a subsequent grain sorghum crop by 1.4 t/ha compared with growth after forage sorghum or burgundy bean”
Claim · model-written summary
Sulla fixed up to 150 kg N/ha.year, the highest among winter legumes.
SullaOrganisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“sulla had the highest total N2 fixation (up to 150 kg N/ha.year)”
Claim · model-written summary
Sulla supplied up to 75 kg N/ha of fixed-N inputs.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“inputs of fixed N (up to 75 kg N/ha)”
t0“Of the winter-growing legumes, sulla had the highest total N2 fixation”
Claim · model-written summary
Sulla produced soil N concentrations 80–100 kg N/ha above oats.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“sulla had the highest total N2 fixation (up to 150 kg N/ha.year) and inputs of fixed N (up to 75 kg N/ha), and resulted in the highest concentrations of soil N (80–100 kg N/ha more than oats)”
Claim · model-written summary
Winter legumes increased subsequent wheat protein.
- Taxon
- Wheat
Triticum aestivume0 - Treatment
- winter legumese0
- Outcome
- proteine0
- Direction
- increasede0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Wheat protein was increased after winter legumes”
Claim · model-written summary
Winter legumes gave no observed wheat yield benefit.
- Taxon
- wheatTriticum aestivume0
- Treatment
- winter legumese0
- Outcome
- yield benefite0
- Direction
- no observede0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Wheat protein was increased after winter legumes, but there was no observed yield benefit for wheat or grain sorghum crops”
Claim · model-written summary
Winter legumes gave no observed grain sorghum yield benefit.
- Taxon
- grain sorghumSorghum bicolore0
- Treatment
- winter legumese0
- Outcome
- yield benefite0
- Direction
- no observede0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Wheat protein was increased after winter legumes, but there was no observed yield benefit for wheat or grain sorghum crops”
Claim · model-written summary
Soil mineral N above 50 kg N/ha greatly reduced forage legume N2 fixation.
Verbatim
e0“high soil mineral N (>50 kg N/ha) greatly reduced N2 fixation by forage legumes”
Claim · model-written summary
Significant legume N2 fixation occurred only when shoot N uptake exceeded initial soil mineral N.
- Taxon
- legumee0
- Organ / stage
- shoote0
- Outcome
- N2 fixatione0
- Qualifier
- shoot N uptake exceeded soil mineral N at the start of the growing seasone0
Not reportedDirection
Verbatim
e0“significant N2 fixation only occurred once legume shoot N uptake exceeded soil mineral N at the start of the growing season”
The same questions in other papers
Medicago sativa · yield · Sorghum bicolor (sorghum)Results agree
1 paper in the same direction as this paper
- positive
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.