ISSN:
1573-5036
Keywords:
Ammonium
;
Classicalvs isotope methods
;
Dinitrogen fixation
;
Glycine max
;
Isolines Isotope techniques
;
Non-nodulating
;
Rhizobium
;
Nitrogen-15
Source:
Springer Online Journal Archives 1860-2000
Topics:
Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
Notes:
Summary Two experiments were carried out with two nodulating and non-nodulating soybean isolines, with three different levels of N as (15NH4)2SO4 at the equivalent of 0, 25 and 50 kg N/ha. In the first experiment three seeds were sown in each pot and the plants harvested at 35, 55 and 75 days. In the second experiment only one seed was sown per pot and harvested at 75 days. Isotope dilution technique and in certain cases natural isotope variation (δ15N) was used to determine directly the origin of nitrogen in the plant, whether from soil, fertilizer or biological N2-fixation. The use of nodulating and non-nodulating isolines enabled comparison with the classical method of estimating N2-fixation by difference from total plant N. Results at the 75 day harvest were similar for either method, but at the earlier harvests, particularly at 35 days, the total-N method was inadequate. The isotope method appeared more sensitive while the total-N method suffered from greater variability with correspondingly high standard errors and significant differences. It was found that by the 35 and 55 day harvests hardly any N2-fixation had taken place, plant nitrogen being almost entirely derived from soil or fertilizer N. Plants in competition used up soil fertilizer N more rapidly, thus stimulating symbiotic nitrogen fixation. When only one plant was grown in each pot it had a greater proportion of N derived from soil or fertilizer, and less N derived from fixation. In general the15N data showed that only about 25% of the applied fertilizer N was absorbed by the plant. The nodulating isoline absorbed more N than the non-nodulating plants. This suggests a possible synergistic effect of N2-fixation on N derived from other sources, giving an increase in total-N content of nudulated plants. The N derived from N2-fixation was scarcely detectable in the roots but appeared to be translocated almost entirely to shoots and pods. With 25 kg N/ha the greater proportion of the nitrogen in the pods was derived from N2-fixation. Even with 50 kg N/ha the nitrogen in the pods derived from fixation remained high, that being derived from fertilizer being less than 15%. About 80% of the nitrogen in the nodules was due to fixation. In the present experiment the application of 25 kg N/ha appeared sufficient to give maximum N absorption by both isolines. At this level symbiotic fixation by Rhizobium remained high in nodulating plants, while the proportion of total N due to fixation was reduced with 50 kg N/ha.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF02140722
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