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1

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Partitioning of biologically fixed nitrogen in cowpea during pod development (1989)

Douglas, L. A. ; Weaver, R. W.

Springer

Plant and soil 116 (1989), S. 129-131

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ISSN: 1573-5036

Keywords: 15N ; nitrogen fixation ; nitrogen partitioning ; translocationVigna unguiculata

Source: Springer Online Journal Archives 1860-2000

Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition

Notes: Abstract Two days after exposure of roots to15N labeled N2, partitioning of biologically fixed N into leaves, stems, peduncles, pods, roots and nodules was measured in the early pod development stage of cowpea (Vigna unguiculata (L.). The experimental objective was to determine the quantity of biologically fixed N that is incorporated into vegetative tissue before being mobilized to pods. For the three varieties of cowpea included in the experiment a maximum of 50% of the N, biologically fixed two days earlier, was contained in the pods. The remaining N was distributed throughout the vegetative portion of the plant with at least 30% in stems and leaves which indicates that much of the newly fixed N must cycle through a N pool in these tissues before reaching the pods.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF02327269

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2

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Herbicide effects on the growth and nodulation potential ofRhizobium trifolii withTrifolium subterraneum L. (1989)

Eberbach, P. L. ; Douglas, L. A.

Springer

Plant and soil 119 (1989), S. 15-23

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ISSN: 1573-5036

Keywords: herbicides ; nodulation ; nutrient solution ; Rhizobium trifolii TA1 ; sub-clover

Source: Springer Online Journal Archives 1860-2000

Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition

Notes: Abstract A study was made of the effect of the herbicides 2,4-D, amitrole, atrazine, chlorsulfuron, diclofop-methyl, diquat, glyphosate, paraquat and trifluralin on the nodulation of sub-clover (Trifolium subterraneum L. ‘Clare’), the growth ofR. trifolii TA1 in liquid nutrient medium and the ability of herbicide-treated inoculum to successfully nodulate sub-clover plants. As concentrations of amitrole, diclofop-methyl and glyphosate in the rooting environment increased from 0 to 20 mg ai L−1, nodulation decreased linearly. The other herbicides at these concentrations caused more severe decreases in nodulation. Growth ofR. trifolii TA1 in nutrient broth was significantly retarded by all concentrations of diquat, 2 mg ai L−1 of paraquat, 10 mg ai L−1 of glyphosate and 2 mg ai L−1 of chlorsulfuron. Other herbicides did not suppress rhizobial growth. Inoculation with TA1 that had been grown in the presence of amitrole, atrazine or glyphosate and then washed free of the herbicide decreased nodulation of sub-clover, indicating that these herbicides may physiologically influence the nodulating potential of certain strains of Rhizobium. The remaining herbicides showed no indications of this effect.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF02370265

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3

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Effect of herbicide residues in a sandy loam on the growth, nodulation and nitrogenase activity (C2H2/C2H4) of Trifolium subterraneum (1991)

Eberbach, P. L. ; Douglas, L. A.

Springer

Plant and soil 131 (1991), S. 67-76

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ISSN: 1573-5036

Keywords: herbicides ; nitrogenase activity ; nodulation ; Trifolium subterraneum

Source: Springer Online Journal Archives 1860-2000

Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition

Notes: Abstract The herbicides 2,4-D, amitrole, atrazine, diclofop-methyl, diquat, paraquat and trifiluralin were applied at rates of 0, 2, 5 and 10 μg ai. g−1 to a sandy loam soil and allowed to degrade for 120 days. After this period, subterranean clover seedlings were transplanted into treated soil and the effect of herbicide residues on plant growth, number of nodules formed and nitrogenase activity was investigated. At all rates of atrazine and chlorsulfuron, and at all rates of amitrole in excess of 2 mg ai g−1 of soil, sufficient herbicide remained to be lethal to the seedlings. When amitrole was applied at the rate of 2 mg ai g−1 of soil, plant growth, nodulation and nitrogenase activity of plants were reduced. Residues of diquat reduced all plant parameters studied while, residues of 2,4-D reduced plant growth and nodule formation, but plant nitrogenase activity was unaffected. Residues of trifluralin had no effect on plant growth parameters but the number of nodules formed per plant was reduced. Residues of paraquat and diclofop-methyl had no effect on any of the plant parameters studied.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00010421

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4

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Assay for soil urease activity (1976)

May, P. B. ; Douglas, L. A.

Springer

Plant and soil 45 (1976), S. 301-305

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ISSN: 1573-5036

Source: Springer Online Journal Archives 1860-2000

Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition

Notes: Summary A procedure is described that allows assay of soil urease activity. The method uses a phosphate buffer (pH 8.8) and a urea substrate concentration of 0.007 M. Incubation for 4 h at 37°C is recommended and urease activity is estimated by determining the amount of ammonium produced by urea hydrolysis in soil. The method is precise, and compares favourably with other procedures. re]19750710

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00011156

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5

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Symbiotic N2 fixation by legumes growing in pots (1983)

Hopmans, P. ; Chalk, P. M. ; Douglas, L. A.

Springer

Plant and soil 74 (1983), S. 325-332

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ISSN: 1573-5036

Keywords: C2H2 reduction ; 15N ; N2 fixation ; Subterranean clover

Source: Springer Online Journal Archives 1860-2000

Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition

Notes: Summary A controlled-environment chamber was designed for exposure of legumes growing in pots to an atmosphere containing N2 enriched in15N. Subterranean clover growing in a sandy loam was exposed for 5 days to an atmosphere with a low15N-enrichment (mean atom %15N excess=1.484). The average amount of atmospheric N2 fixed during this period was 6.05 mg N plant−1. The molar ratio of C2H2 reduced and N2 fixed (C2H2:N2) for subterranean clover was 5.1±0.4. The C2H2 reduction activity of the plants was not significantly affected by the elevated concentration of CO2 (0.60% to 1.40%) in the chamber during the experiment.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF02181350

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6

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Symbiotic N2 fixation by legumes growing in pots (1983)

Hopmans, P. ; Chalk, P. M. ; Douglas, L. A.

Springer

Plant and soil 74 (1983), S. 333-342

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ISSN: 1573-5036

Keywords: Barrel medic ; C2H2 reduction ; 15N ; N2 fixation ; Silver wattle ; Subterranean clover

Source: Springer Online Journal Archives 1860-2000

Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition

Notes: Summary An indirect isotopic method was developed to estimate N2 fixation by legume grown in pots. Two pasture legumes, subterranean clover and barrel medic, and one Australian native legume, silver wattle, were grown in a N2-depleted atmosphere of Ar:O2:CO2 (77:20:3) for a short period of time following addition of15N-labelled KNO3 (8 mg N pot−1). Uptake of fertiliser-N by these plants was compared with that of plants receiving the same amount of15N-labelled NO3 − but grown under a normal N2 atmosphere. Symbiotically fixed N2 was calculated from the difference in fertiliser-N uptake by plants in the Ar and N2 atmospheres, based on the assumption that the nitrogen requirement of the legumes grown in the former atmosphere was satisfied by an equivalent uptake of labelled NO3 −−N from the soil. The percentage decrease in C2H2 reduction activity of the legumes following the addition of KNO3 was relatively constant. The C2H2:N2 molar ratios for subterranean clover, barrel medic and silver wattle were 5.2, 5.8 and 2.8, respectively. A large proportion (50 to 60%) of the electron flux available for N2 fixation by the pasture legumes was used for the evolution of H2. The (C2H2−H2):N2 ratios were close to the theoretical value of 3∶1. The total soil-plant system did not evolve H2, but instead was capable of taking up exogenously supplied H2, which was stimulated by the presence of the legumes.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF02181351

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7

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Distribution of fixed-N and nitrate-N in cowpea during pod development (1993)

Douglas, L. A. ; Weaver, R. W.

Springer

Plant and soil 155-156 (1993), S. 353-354

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ISSN: 1573-5036

Keywords: cowpea ; nitrogen fixation ; nitrate ; partitioning

Source: Springer Online Journal Archives 1860-2000

Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition

Notes: Abstract If the quality and quantity of yields from cowpea (Vigna unguiculata [L.] Walp.) are to be maximised, a complete understanding of the N nutrition of the plant must be achieved. The N requirement for developing pods of this species may come from mobilization of N in vegetative tissue, biological N fixation and uptake of N from soil. In this study, the fate of a pulse of fixed 15N2 or of 15NO3-given to different cowpea plants during pod development was determined. The plants were grown in vermiculite in plastic pots that were able to be sealed with silicone adhesive and equipped with a rubber septum so that 15N2 gas could be injected into the air space above the vermiculite, and gas losses would be eliminated. Nineteen days after injection of 15N2 the pods, leaves, nodules and roots contained 65%, 15%, 9%, and 4%, respectively of the quantity of 15N2 fixed. When 15NO3-15N was taken up by other plants during this period, these plant parts contained 40%, 26%, 3% and 19%, respectively, of the total plant 15N. The percentage 15N in roots was greater, and that of 15N in nodules was lower, when 15NO3-15N was applied than when 15N2 was utilised by plants. These results indicate that, while a high percentage of fixed-N or NO3-N given to cowpea plants moved to the developing pods, other sinks were competing for this newly-aquired N.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00025055

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