Abstract
Replacing summer fallow practices with annual legumes as green manures (LGMs) may increase the sustainability of northern Great Plains wheat (Triticum aestivum L.) systems. Viability hinges on soil water use management and realizing biologically fixed nitrogen (N) benefits. Plot-scale research has shown that managing LGMs with first-flower stage termination and no-till practices conserves soil water and that rotational N benefits can increase wheat grain quality. Nonetheless, farmer adoption of LGMs has been negligible. To better understand this practice and its regional adoption potential, we conducted a participatory on-farm assessment of no-till LGM versus summer fallow–wheat rotations in north-central Montana. Soil water and nitrate (NO3) levels to 0.9 m (3 ft), potentially mineralizable N (PMN) to 0.3 m (1 ft), wheat yields, conservation potential, and producer adoption challenges were assessed at five farmer-managed, field-scale sites. Compared to fallow, LGM treatment diminished mean wheat yield by 6% (0.24 Mg ha−1 [3.7 bu ac−1]), diminished grain protein by 9 g kg−1 when wheat was fertilized with N (p = 0.01), and increased grain protein by 5 g kg−1 when wheat was unfertilized (p = 0.08). Small soil water depletions in LGM treatments below fallow at wheat seeding (17%; 30 mm [1.2 in]) and near-record high rainfall during the wheat growing season (280 to 380 mm [11 to 14 in]) suggest that LGMs likely did not limit soil water available to wheat in this study. Soil NO3 levels following LGMs were 29% to 56% less than summer fallow at wheat seeding, and conversely, greater PMN was detected in LGM treatments at 3 of 5 sites. We theorize that N mineralization from LGMs was insubstantial by wheat seeding due to dry soil conditions and low LGM biomass N contributions, consequently affecting wheat yield potential due to limited early season soil N availability. LGMs increased average use efficiency of available N by 24% during the wheat year and increased total residue carbon (C) and N returned to soils by 260 and 26 kg ha−1 (232 and 23 lb ac−1), respectively, after two years. Our results illustrated that farmers viably managed LGM soil water use with early termination and no-till practices but that LGM adoption may be hindered by a lack of immediate wheat yield or protein benefits from legume-N and seed costs for LGMs. Appropriate incentives, management strategies, and yield benefit expectations (short versus long term) should be fostered to increase the adoption potential of this N-economizing soil and water conservation strategy.
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Claims 13
Claim · model-written summary
Legume green manure diminished mean wheat yield by 6%.
- Taxon
- wheat
Triticum aestivumt0 - Treatment
- LGM treatmente0
- Outcome
- mean wheat yielde0
- Direction
- diminishede0
- Value
- 6%e0
- Qualifier
- 0.24 Mg ha−1 [3.7 bu ac−1]e0
- Comparator
- fallowe0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Compared to fallow, LGM treatment diminished mean wheat yield by 6% (0.24 Mg ha−1 [3.7 bu ac−1])”
t0“wheat (Triticum aestivum L.) systems”
Claim · model-written summary
Legume green manure diminished grain protein by 9 g kg−1 when wheat received nitrogen fertilizer.
- Taxon
- wheatTriticum aestivume0
- Treatment
- LGM treatmente1
- Outcome
- grain proteine0
- Direction
- diminishede0
- Value
- 9 g kg−1e0
- Qualifier
- when wheat was fertilized with N (p = 0.01)e0
- Comparator
- fallowe2
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“diminished grain protein by 9 g kg−1 when wheat was fertilized with N (p = 0.01)”
e1“Compared to fallow, LGM treatment”
e2“Compared to fallow, LGM treatment diminished mean wheat yield by 6% (0.24 Mg ha−1 [3.7 bu ac−1])”
t0“wheat (Triticum aestivum L.) systems”
Claim · model-written summary
Legume green manure increased grain protein by 5 g kg−1 in unfertilized wheat.
- Taxon
- wheatTriticum aestivume0
- Treatment
- LGM treatmente1
- Outcome
- grain proteine0
- Direction
- increasede0
- Value
- 5 g kg−1e0
- Qualifier
- when wheat was unfertilized (p = 0.08)e0
- Comparator
- fallowe2
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“increased grain protein by 5 g kg−1 when wheat was unfertilized (p = 0.08)”
e1“Compared to fallow, LGM treatment”
e2“Compared to fallow, LGM treatment diminished mean wheat yield by 6% (0.24 Mg ha−1 [3.7 bu ac−1])”
t0“wheat (Triticum aestivum L.) systems”
Claim · model-written summary
Green manure treatment had 17% lower soil water at wheat seeding than fallow.
- Taxon
- wheatTriticum aestivume0
- Treatment
- LGM treatmentse0
- Outcome
- Soil water depletionse0
- Direction
- belowe0
- Value
- 17%e0
- Qualifier
- 30 mm [1.2 in]e0
- Comparator
- fallowe0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Soil water depletions in LGM treatments below fallow at wheat seeding (17%; 30 mm [1.2 in])”
Claim · model-written summary
Green manure likely did not limit soil water available to wheat under high rainfall.
- Taxon
- wheatTriticum aestivume0
- Treatment
- LGMse0
- Outcome
- soil water available to wheate0
- Direction
- did not limite0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“LGMs likely did not limit soil water available to wheat in this study”
Claim · model-written summary
Soil nitrate after green manure was 29% to 56% below fallow at wheat seeding.
- Taxon
- wheatTriticum aestivumt0
- Treatment
- LGMse0
- Outcome
- Soil NO3 levelse0
- Direction
- lesse0
- Value
- 29% to 56%e0
- Qualifier
- at wheat seedinge0
- Comparator
- summer fallowe0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Soil NO3 levels following LGMs were 29% to 56% less than summer fallow at wheat seeding”
t0“wheat (Triticum aestivum L.) systems”
Claim · model-written summary
Authors theorized limited green manure nitrogen mineralization by wheat seeding due to dry soil and low biomass nitrogen.
- Taxon
- wheatTriticum aestivume0
- Outcome
- N mineralization from LGMse0
- Qualifier
- dry soil conditions and low LGM biomass N contributionse0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“N mineralization from LGMs was insubstantial by wheat seeding due to dry soil conditions and low LGM biomass N contributions”
Claim · model-written summary
Green manure increased available nitrogen use efficiency by 24% during the wheat year.
- Taxon
- wheatTriticum aestivume0
- Treatment
- LGMse0
- Outcome
- average use efficiency of available Ne0
- Direction
- increasede0
- Value
- 24%e0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“LGMs increased average use efficiency of available N by 24% during the wheat year”
Claim · model-written summary
Green manure increased residue carbon returned to soil by 260 kg ha−1 after two years.
- Taxon
- wheatTriticum aestivumt0
- Treatment
- LGMse1
- Outcome
- total residue carbon (C)e0
- Direction
- increasede0
- Value
- 260e0
- Qualifier
- after two yearse0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“increased total residue carbon (C) and N returned to soils by 260 and 26 kg ha−1 (232 and 23 lb ac−1), respectively, after two years”
e1“LGMs increased average use efficiency of available N”
t0“wheat (Triticum aestivum L.) systems”
Claim · model-written summary
Green manure increased residue nitrogen returned to soil by 26 kg ha−1 after two years.
- Taxon
- wheatTriticum aestivumt0
- Treatment
- LGMse1
- Outcome
- N returned to soilse0
- Direction
- increasede0
- Value
- 26 kg ha−1e0
- Qualifier
- after two yearse0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“increased total residue carbon (C) and N returned to soils by 260 and 26 kg ha−1 (232 and 23 lb ac−1), respectively, after two years”
e1“LGMs increased average use efficiency of available N”
t0“wheat (Triticum aestivum L.) systems”
Claim · model-written summary
Farmers viably managed green manure soil water use through early termination and no-till.
- Taxon
- wheatTriticum aestivumt0
- Outcome
- LGM soil water usee0
- Qualifier
- early termination and no-till practicese0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“farmers viably managed LGM soil water use with early termination and no-till practices”
t0“wheat (Triticum aestivum L.) systems”
Claim · model-written summary
Authors identified lack of immediate wheat yield or protein gains and seed costs as possible adoption barriers.
- Taxon
- wheatTriticum aestivume0
- Outcome
- LGM adoptione0
- Qualifier
- a lack of immediate wheat yield or protein benefits from legume-N and seed costs for LGMse0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“LGM adoption may be hindered by a lack of immediate wheat yield or protein benefits from legume-N and seed costs for LGMs”
Claim · model-written summary
Authors recommended incentives, management strategies and yield expectations to improve green manure adoption.
- Taxon
- wheatTriticum aestivumt0
- Outcome
- Appropriate incentives, management strategies, and yield benefit expectations (short versus long term)e0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Appropriate incentives, management strategies, and yield benefit expectations (short versus long term) should be fostered to increase the adoption potential”
t0“wheat (Triticum aestivum L.) systems”
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