PhD

An investigation was planned during the main growing season, i.e., ‘aman’ (June to November ) to find out the optimum levels of the major inputs for rice cultivation such as nitrogen, phosphate, and water, associated with the management practices like optimum time of harvest, in order to maximize production and to obtain quality paddy which, when processed, should give a high quality rice and thereby high economic return. Keeping the above points in view, four field experiments were conducted during two consecutive ‘aman’ seasons of 1972 and 1973 in a cultivators’ field at abhoy Ashram, Balaramapur which is located about 3 km south – east of the Institute. The farm soil was silty – clay – loam, having a pH of 8.1.
The experiments were conducted with the high – yielding rice variety IR 22 to study its performance under three levels each of nitrogen, phosphate and submergence and laid out in 3 x 3 x 3 confounded design. Nine additional plots to accommodate ‘o’ levels of nitrogen and phosphate were included for fitting production functions. In the first year of experimentation, the nitrogen and phosphate levels were 60, 120 and 180 kg/ha and 30, 60 and 90 kg/ha respectively. In the second year, the levels were 60, 90 and 120 kg N/ha and 30, 45 and 60 kg P2O5/ha. The modification in the levels of nitrogen and phosphate, in the second year, were made on the basis of the findings of the first year of experimentation. In both the years, the levels of submergence were kept constant, i.e., 0 – 5 cm, 5 + 2 cm, and 10 + 2 cm. For finding out the optimum grain moisture at harvest, suitable for higher milling yield, the crop was harvested at 25.5 – 22.5, 22.5 – 19.5 – 16.5 and 16.5 – 13.5 per cent grain moisture. The optimum levels of each input for maximizing grain yield and head yield were found out by fitting production functions.
To identify a suitable variety under a specific management of production and processing, four high yielding rice varieties – Sona, Jayanthi, Pankaj and IR 22 were grown in ‘aman’ season of 1972 and 1973 with similar levels of nitrogen and phosphate as mentioned in Experiments 1 and 2; an additional treatment, with nitrogen and phosphate at ‘o’ level was also included. These experiments were laid out in 4 x 4 x 4 confounded design. The crop was grown under continuous submergence of 5 +2 cm and was harvested at grain moisture content ranging between 19.5 and 16.5 per cent.
Treatment wise experimental details and the salient findings are given in the following pages.
Positive response with reference to grain yield, total mill yield and head yield of variety IR 22 was noted up to 90 kg N/ha and 45 kg P2O5/ha. Further increase in nitrogen and phosphate levels to 120 kg/ha and 60 kg/ha respectively did not and its percentage was minimized by harvesting the crop above 19.5 per cent grain moisture or between 26 and 30 days after flowering. However, by increasing the level of nitrogen from 90 to 120 kg/ha and 120 to 180 kg/ha, the head yield and its recovery percent was less affected even when the crop was harvested with some delay, i.e., between 19.5 and 16.5 per cent grain moisture or between 35 and 37 days after flowering.
The influence of phosphate on grain yield and milling quality, particularly head yield recovery percentage, was more pronounced when considered in combination with grain moisture at harvest.
A suitable water management practice, of growing the crop with shallow submergence of 5 + 2 cm was found beneficial in increasing the yield as well as the milling and head yields. The influence of submergence on the head yield recovery percentage was, however, not to the same extent as that of nitrogen and grain moisture at harvest.
On fitting the function, for variety IR 22, it could be ascertained that maximum grain yield to the extent of 5112 kg/ha can be attained with the optimum levels of 119 kg N/ha, 59 kg P2O5/ha, 149 cm of water and 22.4 per cent grain moisture at harvest which corresponded to harvesting the crop about 30 days after flowering. On the other hand, maximum head yield to the extent of 3562 kg/ha can be attained with the optimum levels of 124 kg N/ha, 51 kg P2O5/ha, 159 cm of water and around 26 per cent grain moisture at harvest which corresponded to harvesting the crop about 26 days after flowering.
The grain yield and consequently, the gross and net returns were maximum under the same levels of nitrogen, phosphate, submergence and grain moisture at harvest. However, from an assessment of rough rice and polished rice along with broken, bran and husk, it was ascertained that the increase in net return to the extent of 984 k/ha was possible only by processing the rough rice.
The positive response in grain yield of all the varieties was found only up to 90 kg N/ha and 45 kg P2O5/ha. In varietal comparison, grain yield, mill yield, head yield and net return were found to be maximum in case of the variety Pankaj, amounting to 5192 kg/ha, 3768 kg/ha, 3027 kg/ha and 1716 Rs/ha respectively. The variety Pankaj was followed by IR 22, Sona and Jayanthi in order. However, in milling quality, particularly head yield recovery percent, IR 22 was found superior to all the other varieties. Further, the variety IR 22, with along and slender grains, proved superior in quality to Pankaj, with long and bold grain. The former, eventually, has higher market value that brought higher return. These characteristics in IR 22 narrowed the difference in profit, when compared to Pankaj, though the latter has significantly higher grain yield the additional net return over milled rice was estimated at 877 Rs/ha in case of IR 22 and 833 Rs/ha in case of Pankaj.
The agro – climatic conditions of this region of West Bengal, where rice is the only crop during ‘aman’, provide better prospects for cultivation of variety IR 22 as well as Pankaj. In quality criteria as well as growing period, IR 22 may prove superior to Pankaj. Their cultivation for higher yield and quality rice is possible only through suitable levels of fertility and water inputs as well as management input which includes the timeliness of operations, particularly harvesting, because it has a greater impact on the final outturn of the produce as quality rice.