Abstract

                                Thirty one years of rainfall data of Aruppukottai in Virudhunagar district were analysed for variability indicated the "Uni" model distribution pattern. Weekly rainfall prediction were made for dry seeding on vertisols. Thrity seventh STD week (Sep 10-16) had the probability of 73 per cent for 20 mm rainfall. The probability for 10 mm of rainfall in the subsequent weeks remained more than 60 per cent. Dry seeding possibility in sorghum and cotton during 35 and 36th week has been indicated. A model with minimum assured rainfall at 50 per cent probability in conjunciton with moisture availability index was developed and validated through on-farm trials in the farmers holdings. The yield increase in sorghum was 36 per cent over the monsoon crops. This technique was useful for other vertisol areas with uni model rainfall pattern with primary peak in the month of October.

Key words : Rainfall prediction, dry seeding, vertisols