Summary
The ability of Azolla pinnata to grow and establish itself in monoculture in rice fields was examined in several locations, falling within different agro-ecological zones of Sri Lanka. Rapid growth of Azolla was observed in all the localities examined. Periodic phosphorus additions and standing water were essential requirements for Azolla growth in rice fields.
The rate of growth of Azolla was measured during two rice growing seasons at Ambalantota, in the low country dry zone where the terrain is undulating to flat, the rice soils are of the low humic gley type and the 75% expectancy value of annual rainfall is below 500 mm. The rice soil pH in this locality is around 6.8, the diurnal light intensity varies from 5 to 130 Klux, with a daily temperature variation of 25 to 37°C. Fresh weight biomass values of Azolla measured over 2 and 3 week periods, during two seasons, gave doubling times of 4.8 and 3.9 days. The corresponding rates of ARA were 2.31 × 10 −6 and 2.73 × 10−6 Mol C2H4 /g (f.w.)/h. These values are approximately equivalent to 230 to 350 g N/ha/h, when converted on a 1:4 (nitrogen fixed: ethylene produced) ratio in relation to the corresponding Azolla biomasses.
Two incorporations of Azolla (grown in dual culture with rice) during a single crop cycle, resulted in grain yields equivalent to fields that received 55 to 84 Kg N/ha of chemical nitrogen fertilizer. Azolla in dual culture with rice also brought about a 50% reduction in weed growth.
Azolla growth with rice under different planting patterns produced grain yield increases of 13, 22 and 47% respectively, in broadcast seeded, transplanted and avenue planted rice over control plots that received no nitrogen under the same planting patterns.
These results provide encouraging evidence for:
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the ability of Azolla pinnata to grow rapidly in several rice growing areas in Sri Lanka;
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the suitability of Azolla as a biofertilizer for rice, that can replace a substantial amount of nitrogenous fertilizer
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© 1984 Martinus Nijhoff/Dr W. Junk Publishers, Dordrecht
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Kulasooriya, S.A., Hirimburegama, W.K., Abeysekera, S.W. (1984). Azolla as a biofertilizer for rice in Sri Lanka. In: Silver, W.S., Schröder, E.C. (eds) Practical Application of Azolla for Rice Production. Developments in Plant and Soil Sciences, vol 13. Springer, Dordrecht. https://doi.org/10.1007/978-94-009-6201-9_18
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DOI: https://doi.org/10.1007/978-94-009-6201-9_18
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