A pot experiment was carried out using a Bangladesh sandy loam paddy soil of pH 6.9 to compare the rates at which nitrogen from Azolla and ammonium sulphate was available to a high yielding rice variety, IR8, grown for 60 days in pots with 4 cm standing flood water.15N tracer studies confirm that nitrogen from ammonium sulphate was more available to the rice plants than from Azolla. An application of 6, 9 and 18 mg N of Azolla pot−1 (each pot contained 250 g soil) increased shoot dry matter yields by 13, 29 and 49% for an uptake of 19, 36 and 85% more nitrogen; the corresponding increases on using ammonium sulphate were 33, 54 and 114% for an increased uptake of 57, 90 and 177% more nitrogen, respectively. About 34% of applied15N of Azolla was taken up by the rice plants in 60 days but 61% of15N of the ammonium sulphate was absorbed during this period. About 45% of the Azolla-N was released in 60 days, 55% remained in the soils as undecomposed material and 11% was lost as gas. The gaseous loss of15N from ammonium sulphate was 14%; 25% remained in the soils.
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Mian, M.H., Stewart, W.D.P. A15N tracer study to compare nitrogen supply by Azolla and ammonium sulphate to IR8 rice plants grown under flooded conditions. Plant Soil 83, 371–379 (1985). https://doi.org/10.1007/BF02184449
- Ammonium sulphate
- Flooded soils
- 15N tracer
- Nitrogen uptake