Varietal Comparison of Bt and Non-Bt Cotton (Gossypium hirsutum L.) Under Different Sowing Dates and Nitrogen Rates.

To compare the effect of different sowing dates and nitrogen levels on phenological components and seed cotton yield of Bt and non-Bt cotton, an experiment was laid out on Agronomic Research Area in University of Agriculture, Faisalabad during Kharif 2009 and 2010. The experimental area is located at 73.09^o East longitude, 31.25^o North latitude and at an altitude of 183 meters above sea level. The experiment was laid out in randomized complete block design (RCBD) with split-split arrangement and replicated thrice. Two cotton cultivars; FH-113 (Bt) and CIM-496 (non-Bt) were planted at two different times (mid March and mid May) using three nitrogen levels (115 kg ha^-1, 145 kg ha^-1 and 175 kg ha^-1). Planting times were placed in main plots, varieties in sub plots and N levels in sub sub plots.  Plot size was 6 m x 3 m with row to row spacing of 0.75 m and plant to plant spacing of 0.30 m. All the interactions were non significant for parameters under discussion except variety x sowing date for seed cotton yield. Mean values showed that more number of days from planting to appearance of first floral bud, first flower and first boll splition were recorded in mid March planting than mid May planting during 2009 as well as in 2010 however, vertical as well as horizontal flower intervals remained unaffected. Varietal comparison recorded more days for appearance of first flower and first boll splition as well as maximum vertical flower interval and horizontal flower interval in CIM-496 than in FH-113 during both years of study. Among nitrogen levels maximum number of days from planting to appearance of first floral bud, first flower and first boll splition  were recorded with 175 kg N ha^-1 and minimum values were recorded with 115 kg N ha^-1 in 2009 and 2010 while vertical and horizontal flower intervals remained unaffected. Statistically maximum seed cotton yield was recorded in FH-113 at mid March planting and minimum was recorded in CIM-496 at mid May planting, while CIM-496 at mid March planting was at par with FH-113 at mid May planting. Amongst the nitrogen levels, 145 kg ha^-1 gave maximum seed cotton yield which was at par with 175 kg ha^-1 while 115 kg ha^-1 gave minimum seed cotton yield in 2009 and 2010.