INFLUENCE OF DATE OF SOWING ON REQUIREMENT OF THERMAL INDEXES OF WHEAT (TRITICUM-AESTIVUM) VARIETIES

Requirement of thermal units for flowering and maturity in 10 varietie s of wheat (Triticum aestivum L. emend. Fiori & Paol.) tinder 3 dates of sowing was determined. The requirement of thermal indices like grow ing degree-days, remainder index and exponential index was greatly red uced for flowering and maturity when wheat was sown late. However, the heliothermal units linearly increased for powering with delay in sowi ng and the reverse was observed at maturity. The recorded physiologica l index was opposite to the heliothermal units. The heat-use efficienc y declined when sown either early or late. A delay of 15 days in sowin g increased the days to flowering by 1 day (delayed flowering) and red uced the days to maturity by 10 days (early maturity). The highest see d yield was noted in 'Lok 1' in all the 3 dates of sowing. The optimum time for wheat sowing was the second week of November, which was al p ar with third week of October. Correlation of physiological index and heat-use efficiency with seed yield revealed that the association was positively significant in all the dates of sowing and the association of the remaining thermal indices with seed yield was negative.