Estimates of nitrogen fixations by legumes in alternate cropping systems at Warra, Queensland, using enriched 15N dilution and natural 15N abundance techniques
1995
Hossain, S.A. | Waring, S.A. (Queensland Univ., St. Lucia (Australia). Dept. of Agriculture) | Hossain, S.A. (Dhaka Univ., (Bangladesh). Dept. of Soil Science) | Strong, W.M. | Dalal, R.C. | Weston, E.J. (Queensland Dept. of Primary Industries, Toowoomba (Australia))
Nitrogen fixation was measured using two isotopic techniques over 2 years as part of a long-term field experiment established to test alternative management strategies for restoring fertility in a vertisol at Warra, Southern Queensland. Treatments containing legumes were: grass-legume ley for 4 years followed by 4 years of wheat; a 2-year rotation of lucerne and wheat; a 2-year rotation of medic and wheat; and a 2-year rotation of chickpea and wheat. For the enriched- 15N procedure, the proportion of N derived from air (% Ndfa) for the grass-legume and lucerne and medic leys ranged from 67 to 97%, and averaged 85%, with little evidence for effects of season, pasture establishment, time or species. The percentage Ndfa for chickpea was significantly lower (62%). Values for the natural abundance 15N procedure were mostly lower and more variable than for the enriched method. It was concluded that the enriched procedure provided more reliable estimates of N2 fixed by the legumes. The dry matter yield of the legumes in leys, mainly lucerne, was closely associated with the amount of N2 fixed, with a value of 28 kg of N2 fixed for each tonne of dry matter produced.
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