Abstract

                                Investigations were carried out to quantify the effect of photothermal, anits (PTU) or heat degree units and Solar Radiation levels (SR) in growth, yield com ponents and yield of hybrid cotton Varalakshmi. A mean reduction in seed cotton yield to the tune of 3.1 g/ha was observed when the date of sowing was shifted from 15th August to 13th September. The regression co-efficients revealed that SR levels had a significent positive effect on plant height. LAI and dry matter pro- duction. Seventy seven and 74 per cent of the variations respectively in boll number and seed cotton yield were contributed by the SR levels. It is predicted that an accumulated PTU of 27,000 and SR of 40,000 Cal-cm are required to obtain 39 q/ha of seed cotton which could be achieved when sowings are taken up in the middle of August under Coimbatore conditions.

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