Sreedharan, CSreedevi, PKAU2019-05-092019-05-091985171042http://krishikosh.egranth.ac.in/handle/1/5810102655PhDThree field experiments were conducted at the Regional Agricultural Research Station, Pattambi, Kerala to evaluate some of the low cost agronomic techniques for sustained rice production during the period from 1982 to 1985. In the first experiment the performance of IR 42, a rice variety suited to low fertility conditions was assessed under varying levels of nutrition and spacing. Fertilizer, age of seedlings and planting density, for IR 42 were the experimental variables for the second experiment. In the third trial, azolla was evaluated as a low cost biofertilizer for IR 42. The first and third trials were laid out in split plot design while the second trial in factorial RBD. The rice cultivar IR 42 proved its mettle under the low fertility conditions. In fact, it gave an average yield of 2.78 t ha-1 in virippu and 2.32 t ha-1 in mundakan without any fertilizer application. A plant population of 33 hills m-2 (spacing 20 x 15 cm) in conjunction with full dose of fertilizer of 90 : 45 :45 kg NPK ha-1 recorded substantially more grain yield of 4.24 and 3.20 t ha-1 in virippu and mundakan seasons, respectively. Relatively lower grain and straw yields were registered by the treatment 100 hills m-2 (spacing 20 x 5 cm) at all levels of fertilizer application. The net return and benefit cost ratio were more in the former combination. Increasing the seedling number hill-1 from two to four or six was also found to be beneficial for this variety. At lower levels of fertilizer six seedlings hill-1 recorded higher grain yields. However, at higher levels four seedlings hill-1 was found to be superior. During virippu season planting of 35 days old seedlings was found to perform better compared to 30 and 25 days old seedlings whereas in mundakan season, 30 days old seedlings were found preferable in terms of grain yield. Recommended dose of fertilizers (90 : 45 : 45 kg NPK ha-1) with azolla @ 10 t ha-1 and 75 per cent of the same with azolla @ 15 t ha-1 recorded similar grain yields indicating that an extra dose of 5 t of azolla ha-1 could substantially reduce the chemical fertilizer requirement and save as much as 25 per cent of the fertilizer. The benefit cost ratios were almost equal in both the combinations while the return per rupee invested was more in the latter combination. The finding appears to caution against excessive use of azolla expecting better exploitation of all the benefits attributed to it. Nevertheless, data on the residual fertility of the soil after each crop indicate that residual fertility was higher in the plots receiving full dose of fertilizer along with the highest level of azolla, 20 t ha-1.ennullThesis