Effect of geographical parameters, sowing date and flowering duration on grain yield of rice*

Coordinated rice experimental data of 5 varieties belonging to different maturity groups for 5 years (1985–90) grown during the wet seasons was scanned to study the relationship between grain yield and latitude, longitude, altitude, sowing date and days to 50 per cent flowering from amongst 60 test locations in the country. Longitude and days to 50 per cent flowering had a significant effect on grain yield in all the 5 varieties. From the cause effect analysis, it was noticed that relatively dry weather favours higher grain yield besides more days to flowering. Further, it was pointed out that low grain yoields in Eastern India could be attributed to high relative humidity, higher night temperture coupled with low evapotranspiration values resulting in low nutrients uptake.