Competition for ¹⁵N labelled ammonium between Trifolium subterraneum L. and Lolium multiflorum L. when grown in a mixture
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| Other Authors: | , |
| Format: | Thesis Book |
| Language: | English |
| Published: |
1985.
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| Subjects: | |
| Online Access: | Link to OAKTrust copy Link to ProQuest copy |
| Abstract: | Grasses and legumes are often grown in association in pastures because total herbage yield and forage quality is often higher than a monoculture grass sward. The competitive ability of the forage species for mineral N influences the stability of the mixed pasture. 'Mt. Barker' subterranean clover (Trifolium subterraneum L.) and 'Gulf' ryegrass (Lolium multiflorum L.) were grown in pure stands and in mixtures in 3.8 1 pots filled with exploded vermiculite to quantify the competition for applied mineral nitrogen (N). The isotope dilution technique using ^15NH4 was used. Also, the effect of increasing rates of fertilizer N on nodulation and fixation by subterranean clover and the rate of N uptake of subterranean clover and ryegrass was measured. The acetylene-ethylene technique and a nodulation rating were used to examine the effect of N fertilization on fixation and nodulation. The uptake of N fertilizer by subterranean clover and ryegrass in both pure stands and the mixtures increased as the rate of fertilizer N applied increased. When grown in a pure stand, subterranean clover recovered a comparable amount of fertilizer N, but when grown in mixture with ryegrass, subterranean clover recovered only from 2 to 45 mg of N. Ryegrass growing alone recovered from 44 to 364 mg of N. Consequently, the percentage of total N fixed by the legume in a pure stand decreased from 100 to 2.3% and in the mixture decreased from 100 to 36.8%. By increasing the rate of fertilizer N at planting, C2H2 reduction decreased and the nodulation ratings of subterranean clover also decreased. However, increasing the rate of fertilizer N after seedling establishment decreased nitrogenase activity only at the highest rate of N fertilization. Also, the nodulation rating of subterranean clover was not greatly affected. Ryegrass recovered 2 times the amount of labelled N in 6 hours than subterranean clover. The rate of N uptake was not due to differences in root fresh weight or dry weight. Ryegrass appeared to be a better competitor for NH4 than subterranean clover because of the greater rate of uptake. |
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| Item Description: | Typescript (photocopy). Vita. "Major subject: Agronomy." |
| Physical Description: | xi, 119 leaves ; 29 cm |
| Bibliography: | Includes bibliographical references (leaves 85-91). |