Nitrogen fixation and accretion of soil nitrogen by field-grown lupins ( Lupinus angustifolius)

• Published in: Field crops research 1987-07, Vol.16 (4), p.309-322
• Main Authors: Evans, J., Turner, G.L., O'Connor, G.E., Bergersen, F.J.
• Format: Article
• Language: English
• Subjects: Agronomy. Soil science and plant productions; Biological and medical sciences; Economic plant physiology; Fundamental and applied biological sciences. Psychology; Symbiosis (nodules, symbiotic nitrogen fixation, mycorrhiza...)
• ISSN: 0378-4290; 1872-6852
• DOI: 10.1016/0378-4290(87)90069-4

In Lupinus angustifolius cv. Illyarrie, the above-ground N derived from symbiotically fixed N 2 was estimated in field crops grown on red-earth loam over two seasons. The proportion was estimated by 15N isotope dilution with procedures using the natural abundance of 15N and enrichment of soil N with K 15NO 3, and two reference species, wheat and linseed. To allow for fractionation of 15N in lupin, the natural abundance of 15N in lupin shoots and other plant parts was determined under N 2-dependent growth. The proportion of fixed N 2 varied between years, sowing date and reference species. As much as 85% (255 kg N ha −1), and as little as 49% (78 kg N ha −1) of lupin N came from fixed N 2. Proportions derived from natural abundance and enrichment were similar, but linseed gave estimates of fixed N 2 by lupins higher than those derived with wheat. After allowing for removal of N in harvested grain, the potential benefit of lupin to soil N varied from 34 to 138 kg N ha −1 across years and sowing date. From the derived N budget there was a strong possibility that higher levels of mineral N after lupin than after wheat were due to less-efficient use of soil mineral N by nodulated lupin.