SummaryAzolla and blue-green algae (BGA) biofertilizers in rice cultures were compared with farmyard manure (FYM), Azolla and Eichhornia compost, green manuring with Sesbania and chemical nitrogen fertilizer as urea. Growing Azolla crop in rice field once before transplanting and twice after transplanting produced a fresh biomass of Azolla of 46·7–47·6 and 36·4–40·6 t/ha, containing 83·4–92·2 and 64·7–70·4 kg N/ha, with the rice varieties IR-36 and Mahsuri, respectively. The BGA produced only 7·9–8·9 and 5·2–7·2 t fresh biomass/ha, containing 19·5–20·6 and 14·8–19·3 kg N/ha with IR-36 and Mahsuri, respectively.In the 1st year of the experiment application of FYM, Eichhornia and Azolla compost and green manuring of Sesbania produced lower grain and straw yields and panicles than 60 kg N/ha as urea, but during the 2nd year all these treatments showed responses equal to that of 60 kg N/ha as urea. Nitrogen concentration and uptake by rice in these treatments were, however, lower than that of 60 kg N/ha as urea. Growing and incorporating Azolla once before and twice after transplanting produced higher grain and straw yields, and more panicles, and also showed higher nitrogen concentration and uptake by rice than those of organic and green manures. The BGA inoculation to rice with 30 kg N/ha as urea produced less grain and straw, and fewer panicles, and also showed lower nitrogen concentration and uptake by rice than 60 kg N/ha as urea and other organic manures. Of the two rice varieties, IR-36 produced more grain and panicles than Mahsuri, but Mahsuri produced more straw.Total nitrogen, organic carbon and available phosphorus of soil after harvest of the rice increased owing to the application of organic manures, green manures and Azolla and BGA biofertilizers. The green manuring of Sesbania and using Azolla once before and twice after transplanting and FYM showed highest organic carbon and available phosphorus in soil after harvest.
Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition