Abstract
A technique of 15N isotope dilution was used to quantify N2 fixation by Azolla and the availability of Azolla-N and urea-N to rice plants. Labelled urea and Azolla, alone or as a mixture, were studied in normal and sterilized soils. A total of 40 kg N fed−1 was applied as urea, Azolla or Azolla and urea in combination, to rice plants grown in pots. Urea or Azolla, applied at equal rates of 40 kg N fed−1, were equally effective for increasing the dry mass of shoots and roots over control. A similar effect was observed with N percent and N uptake by the crop, both in normal and sterilized soil. Generally, all parameters were higher in sterilized soil than in normal soil. The proportion of N uptake which was derived from urea (%NdfU) and that from Azolla (%NdfAz) were identical for treatments receiving the same N rate. 15N recovery by shoots and roots from urea or Azolla was essentially identical. Nitrogen derived from air (%Ndfa) ranged between 57% and 67% according to soil treatment and organ of plant. The Ndfa was significantly correlated with both the dry mass and N uptake by the rice crop.
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Galal, Y.G.M. (1996). Estimation of nitrogen fixation in Azolla—rice association using 15N isotope dilution. In: Rahman, M., Podder, A.K., Van Hove, C., Begum, Z.N.T., Heulin, T., Hartmann, A. (eds) Biological Nitrogen Fixation Associated with Rice Production. Developments in Plant and Soil Sciences, vol 70. Springer, Dordrecht. https://doi.org/10.1007/978-94-015-8670-2_13
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DOI: https://doi.org/10.1007/978-94-015-8670-2_13
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