Impact de l'association sur le niveau de nutrition azotée et la croissance du ray-grass anglais et du trèfle blanc

Soussana, Jean‐François; Arregui, MC

doi:10.1051/agro:19950201

Cited by 15 publications

(11 citation statements)

References 17 publications

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“…Carbohydrate accumulation in plant organs and/ or shifts in the composition of the harvested material in favor of plant fractions of low N concentration may contribute to a reduction in the N concentration in the total above-ground biomass. In fact, a consistent decrease in the leaf-to-petiole ratio, known to correspond to a reduced N concentration in the above- Table I. ground material in T. repens (Soussana and Arregui, 1995), was also observed under elevated pC0, in our experiment. Consistent with this observation are the results of specific harvests (May 17 and July 12,1994) that showed that under elevated pC0, the N concentration of leaf blade material was reduced by only 7% compared with the total aboveground material, which was reduced by 10%.…”

Section: Effect Of Elevated Pc0 On N Yield Of T Repens and On The Nsupporting

confidence: 85%

Stimulation of Symbiotic N2 Fixation in Trifolium repens L. under Elevated Atmospheric pCO2 in a Grassland Ecosystem

et al. 1996

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~Symbiotic N, fixation is one of the main processes that introduces N into terrestrial ecosystems. As such, it may be crucial for the sequestration of the extra C available in a world of continuously increasing atmospheric CO, partial pressure (pC0,). The effect of elevated pC0, (60 Pa) on symbiotic N, fixation ('5N-isotope dilution method) was investigated using Free-Air-C0,-Enrichment technology over a period of 3 years. Trifolium repens was cultivated either alone or together with Lolium perenne (a nonfixing reference crop) in mixed swards. Two different N fertilization levels and defoliation frequencies were applied. The total N yield increased consistently and the percentage of plant N derived from symbiotic N, fixation increased significantly in T. repens under elevated pC0,. All additionally assimilated N was derived from symbiotic N, fixation, not from the soil. In the mixtures exposed to elevated pCO,, an increased amount of symbiotically fixed N (+7.8,8.2, and 6.2 g m-' a-' in 1993, 1994, and 1995, respectively) was introduced into the system. lncreased N, fixation is a competitive advantage for T. repens in mixed swards with pasture grasses and may be a crucial factor in maintaining the C:N ratio in the ecosystem as a whole.

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Section: Effect Of Elevated Pc0 On N Yield Of T Repens and On The Nsupporting

confidence: 85%

Stimulation of Symbiotic N2 Fixation in Trifolium repens L. under Elevated Atmospheric pCO2 in a Grassland Ecosystem

et al. 1996

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“… Index of percentage grass N nutrition in pure (▮) and mixed swards (□) on initially N‐poor (······) and N‐rich (––––) soils. The Index of percentage grass N nutrition is expressed as the ratio (%) between the actual N concentration and the concentration non‐limiting to growth (Lemaire and Salette, 1984; Soussana and Arregui, 1995) for initially poor and rich soils (SoilN below 150 and above 200 kg N ha –1 year –1 respectively). Vertical bars represent confidence interval at 95%.…”

Section: Resultsmentioning

confidence: 99%

“…This suggests that the mixed swards behave like a pure grass sward in the first stage of establishment, as shown by the positive correlation between SoilN and N yield for both species at the first regrowth of the first year (Figure 6a). Nevertheless, the higher SoilN productivity for the grass confirms that the grass is more efficient in the uptake of mineral N than the competing clover (Danso et al ., 1988; Soussana and Arregui, 1995).…”

Section: Discussionmentioning

confidence: 99%

“…A lower SoilN productivity for the mixed sward compared with that for the pure clover (Table 4) also reflects the competition between grass and clover. SoilN increased the production of the pure clover but decreased the production of the clover in the mixed sward, owing to the better competitive ability of the companion grass for N uptake and light interception (Soussana and Arregui, 1995). A lower SoilN productivity of the grass in the mixture compared with the pure grass occurred when previously higher clover growth in the poorer soils had compensated for the initial differences in soil N‐supplying capacities, therefore increasing the competitiveness of the grass growing in the poorer soils.…”

Section: Discussionmentioning

confidence: 99%

“…The N nutrition index (Nut) of the grass was calculated as the quotient of the measured N concentration in the harvests (Nh) and the critical N concentration (Nc) at the same standing dry matter (DM, t ha –1 ), and this N nutrition index was expressed in a percentage: Nut=100 × Nh/Nc. For the mixed swards, Nh was the N concentration of the grass and DM was the harvested dry matter of the whole mixture (Soussana and Arregui, 1995).…”

Section: Methodsmentioning

confidence: 99%

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Soil N contributes to the oscillations of the white clover content in mixed swards of perennial ryegrass under conditions that simulate grazing over five years

Loiseau¹,

Soussana²,

Louault³

et al. 2001

Grass and Forage Science

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The effect of the initial N‐supplying capacity of soils (SoilN, 90–230 kg N ha–1 year–1) was tested on the dry‐matter and N yields of pure or mixed white clover and perennial ryegrass swards, managed under simulated grazing over a 5‐year period. The cumulated N harvested in the mixed swards was similar, both for white clover and perennial ryegrass, but the proportion of white clover showed oscillations over a 2‐year period. In the first year, the SoilN effect was similar to that of fertilizer N. During the course of the experiment, the effect was always positive on the pure perennial ryegrass sward, alternately negative and nil for the white clover in the mixed sward and alternately positive and nil for the perennial ryegrass in the mixed sward; the period of these oscillations was 2 years. From the third regrowth period after sowing, the ratio between the actual N concentration and the concentration non‐limiting to growth for the perennial ryegrass in the mixed sward, increased above that of the pure perennial ryegrass sward. It was in turn greater in the soils that were initially poor and then greater in those that were initially rich in soil N. The periodic oscillation of the initial SoilN effects implies that the initial SoilN gradient was alternately compensated and restored. It was concluded that N fluxes are partly responsible for the temporal oscillations in the proportion of white clover in mixed swards.

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Grasslands

Duru¹,

Lemaire²,

Cruz³

1997

Diagnosis of the Nitrogen Status in Crops

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Impact de l'association sur le niveau de nutrition azotée et la croissance du ray-grass anglais et du trèfle blanc

Cited by 15 publications

References 17 publications

Stimulation of Symbiotic N2 Fixation in Trifolium repens L. under Elevated Atmospheric pCO2 in a Grassland Ecosystem

Stimulation of Symbiotic N2 Fixation in Trifolium repens L. under Elevated Atmospheric pCO2 in a Grassland Ecosystem

Soil N contributes to the oscillations of the white clover content in mixed swards of perennial ryegrass under conditions that simulate grazing over five years

Grasslands

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