ALBERT

Description: SummaryPre-emergence herbicides applied at field recommended doses, 3 days after transplanting (DAT) rice plants, inhibited growth and N2-fixation of Azolla pinnata (Bangkok) and BGA (blue-green algae) inoculated 10 DAT. This inhibition was up to 15 DAT in Azolla and up to 20 DAT in BGA. Butachlor and Oxadiazon resulted in higher toxicity to Azolla and BGA than Benthiocarb and Pendimethalin. The application of 0·5 kg/ha active ingredient of 2,4-DNa did not inhibit growth of Azolla but inhibited BGA growth. However, 2,4-DEE, a post-emergence herbicide, applied 30 DAT showed inhibitory effects on the growth and N2-fixation of both Azolla and BGA. Inoculation of 2·0 t/ha of fresh Azolla 10 DAT produced maximum biomass within 20–25 days of herbicide treatments, depending upon the season. The inoculation of 10 kg/ha of a dry mixture of BGA 10 DAT could produce the maximum biomass 60 and 80 DAT in control and herbicide treated plots, respectively. The biomass and nitrogen produced by Azolla recorded at maximum mat formation were similar in both herbicide treated and untreated plots, but in BGA these were higher in controls than those of herbicide treated plots.The use of Azolla and BGA biofertilizers along with herbicides increased the grain and straw yields, and panicle number and nitrogen uptake, by rice over no Azolla or BGA treatments. The Azolla and BGA treatments even without weeding increased rice yield up to that of herbicide and biofertilizer treatments.

Description: 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.

Description: SummaryThe intercropping of Azolla pinnata (Vietnam) with rice varieties transplanted in rectangular (40×10 cm) and double-narrow-row (15 × 10:65–80 cm) spacings showed faster growth and nitrogen fixation than in square (20 × 20 cm) spacing with the same number of hills per unit area. Inoculation of 2·0 t/ha fresh Azolla, 10 and 30 days after transplanting, produced Azolla mats on the water surface 25 and 50 days after transplanting, respectively. The total fresh biomass of Azolla grown with different rice varieties in square spacing was 26·7–33·0 t/ha; this produced 41·9–61·3 kg N/ha. However, rectangular and double-narrow-row spacing produced 28·7–37·7 and 34·4–39·6 t/ha fresh Azolla containing 53·9–69·0 and 58·0·73–3 kg N/ha, respectively if the rice rows were transplanted in north-south direction and 36·3–41·5 and 40·0–43·7 t/ha fresh biomass containing 63·4–74·2 and 65·3–83·3 kg N/ha, respectively in east-west direction.The grain and straw yields of rice grown in rectangular and double-narrow-row spacing with north-south row orientation were lower than the yields of rice in square spacing, but the east-west row orientation of these spacings showed yields similar to those obtained by growing rice in square spacing.