143 J. Crop and Weed, 16(3) Effect of varying fertility levels on physiological aspects of rice cultivars in the North Western Himalayas N. KUMAR, B. S. MANKOTIA, S. MANUJA, B. PAREEK, P. KUMAR, R. SHARMA AND I. S. MANDIAN Department of Agronomy, Forages and Grassland Management, College of Agriculture CSK Himachal Pradesh Krishi Visvavidyalaya, Palampur 176062, Himachal Pradesh Received : 12.09.2020 ; Revised : 30.09.2020 ; Accepted : 01.10.2020 DOI : https://doi.org/10.22271/09746315.2020.v16.i3.1379 ABSTRACT A field experiment was conducted during kharif 2018 at Rice and Wheat Research Centre (RWRC), Malan to study the physiological response of different rice cultivars to varying fertility levels in mid-hills of Himachal Pradesh. The experiment consisted of 5 main-plot treatments comprising varying fertility levels {50% recommended dose of fertilizer (RDF), 100% RDF (90:40:40 kg N:P:K ha -1 ), 150% RDF, 50% RDF + Azolla and 100% RDF + Azolla} and 4 cultivars as sub-plot treatments {Vivekdhan 65, HPR 2143, HPR 2720 (red rice) and AZ 6508 (hybrid)}. The soil of the experimental site was silty clay loam in texture, acidic in reaction, medium in available nitrogen, phosphorus, and potassium. The increase in fertility level and Azolla application increased the dry matter accumulation and leaf area index of rice. The increasing trend in crop growth rate (CGR) during the active tillering and flowering stage was observed while the leaf area ratio reduced from 60 to 90 days after transplanting (DAT). Contrary to these the relative growth rate (RGR) and net assimilation rate (NAR) remained almost equal during both the time intervals between 30 and 60 days and 60 and 90 days after transplanting though it varied with varying fertility levels as well as between different cultivars. Additional azolla application at both the fertilizer doses of 50 and 100 % RDF showed a significant increase in CGR from 30 to 60 DAT as compared to the when it was not applied, the increase being 2.70 and 2.13 g m -2 day -1 with the azolla application at 50 % and 100 % RDF, respectively. Further CGR recorded between 30 and 60 DAT with the application of azolla with 50 % RDF was statistically similar to the application of 100 % RDF alone, indicating a saving of 50 % RDF with the azolla application. Also the CGR recorded between 30 and 60 DAT with the application of 150 % RDF was also similar to the application of 100 % RDF along with azolla application. Similarly RGR increased with increasing fertilizer application as well as with azolla application at 30 to 60 and 60 to 90 DAT. LAR decreased during the flowering stage due to more contribution of flag leaf in net assimilation. Among the cultivars tested ‘Vivekdhan 65’ and ‘AZ 6508’ showed higher values of CGR as well as RGR, particularly between 60 to 90 DAT while ‘AZ 6508’ had significantly higher LAR. Initially, azolla applied to the crop was not much effective but during the later stages, its contribution increased the growth rate. These findings suggest that growth indices could be enhanced by applying higher doses of fertilizesr but the application of azolla can result in the saving of fertilizers. Keywords: Azolla, crop growth rate, leaf area ratio, net assimilation rate, relative growth rate and rice Rice (Oryza sativa L.) is one of the most important cereal crops that hold the key to food security of the world. Globally, it occupies an area of about 167.13 million ha with a production of 782.02 million tonne (FAOSTAT, 2020). It is the staple food for more than two-third population of the world, especially the people living in Asia where more than 90 percent of rice is produced and consumed. In India, the area under rice is 43.79 million hectares with a total production of 116.42 million tonnes and the average productivity of 2.66 t ha -1 (Anon., 2019). The vast majority of the farmers in the country derive their livelihood from rice cultivation. Nutrient management has played an important role in increasing the productivity of this crop. But the blanket application of the fertilizers, to increase productivity and profitability, has resulted in higher consumption of the nutrients which has ultimately Email: saininitesh08@gmail.com Journal of Crop and Weed, 16(3): 143-147 (2020) ISSN- O : 2349 9400 ; P : 0974 6315 http://cwssbckv.org www.cropandweed.com resulted in lower nutrient use efficiencies, lowered profits, and increased environmental problems (Pamp olino et al., 2012). In addition to the use of Azolla as a source of nitrogen for rice crop, it can also be used for reclaiming saline soils, reducing evapotranspiration, and to control weed infestations in rice crop (Van Hove and Lejeune 1996). Extensive work has been done on the exploitation of Azollaas a bio-fertilizer in rice in many states of our country, however, limited systematic studies have so far been made in Himachal Pradesh about the usefulness of Azollain rice production (Thakur, 2013). Azolla can also be used to purify wastewater as it can accumulate P and some heavy metals from water (Sarkar and Jana 1986). Increasing the fertilizer doses have brought increment in growth indices (plant height, tillers, DM, LAI, CGR, RGR, NAR, photosynthetic rate), yield and protein content of rice (Rajput et al., 2017).