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Comparative studies on different methods of Azolla utilization in rice culture
Published online by Cambridge University Press: 27 March 2009
Summary
Inoculation of 3·0 t of fresh Azolla pinnata (Bangkok) per hectare 15 days before transplanting, 10 and 30 days after transplanting produced Azolla mats on the water surface 10, 12 and 15 days after inoculation, respectively. The Azolla growth and N2-fixation before transplanting were more than that after transplanting. Growing Azolla once before transplanting and twice after transplanting produced a total of 51·0–52·8 t fresh Azolla/ha, which fixed 92·8–96·0 kg nitrogen, whereas growing it once before transplanting plus once after transplanting and twice after transplanting produced 35·0–40·0 and 29·0–37·5 t fresh Azolla/h, and fixed 660·–72·4 and 52·5–66·1 kg N, respectively.
Application of Azolla increased the plant height, tillering, grain and straw yields of rice and also the fertility of the soil at harvest. Growing and incorporating Azolla once before transplanting and twice after transplanting of rice increased the grain and straw yields significantly more than applying 60 kg N/ha as urea and showed greater effect on soil fertility.
Growing Azolla before or after transplanting the rice in combination with 30 kg N/ha as urea and Azolla once before transplanting and once after transplanting without incorporation gave responses similar to that obtained by a divided application of 60 kg N/ha as urea. Growing and incorporating Azolla twice after transplanting showed slightly less response than growing it once before and once after transplanting and giving 60 kg N/ha as urea but slightly more than giving 45 kg N/ha as urea. The Azolla pinnata collected from Bangkok and Vietnam when used once before transplanting at equal biomass (15·0 t/ha fresh Azolla) together with a top dressing of 30 kg N/ha as urea showed a similar response in the rice crop.
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