Phosphorus availability from incorporated zolla in flooded rice soils
1995
Papit Sangtong | Pichit Pongsakul (Department of Agriculture, Bangkok (Thailand). Soil Science Div. Soil Chemistry Research Group)
Azolla spp. is accepted to be nitrogen biofertilizer for rice. Phosphate fertilization azolla is neccessary to increase the efficiency of azolla as nitrogen fertilizer. Thus decomposition of azolla should release not only N but also P. To clarify this information, the experiment using incubation technique has been conducted. Azolla at the rate of 3 tons/rai was incorporated with 4 series of soils: Rangsit (Sulfic Tropaquepts), sanphaya (Typic Ustifluvents), Lampang (Typic Tropaqualfs) and Roi Et (Aeric Paleaquults) for periods of 1, 2, 3, 4, 6 and 8 weeks. Results showed that azolla incorporation with soils increased P availability within 3 weeks of incubation. Phosphorus availability of Roi Et, Lampang, Sanphaya and Rangsit soils were 110, 105, 92 and 36 mg/kg, respectively. The availability of P decreased after 3 weeks and remained relatively constant during 4-8 weeks of incubation, but these P values are enough for rice growth. Thus P fertilization may not be needed if azolla was applied enough phosphate fertilizer. However, P availability from incorporated azolla was influenced by soil condition and soil microbial activities.
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