Microclimatic influence on thermal time requirement, growth dynamics and yield attributes of cotton in the South-Western region Of Punjab

To quantify thermal requirement for Bt cotton hybrid using Agrometeorological indices, multi-location field experiments were undertaken at Punjab Agricultural University (PAU) Regional Research Station, Bathinda and PAU Regional Research Station, Faridkot during kharif 2018. The experiment consisted of three sowing dates i.e. April 30^th, May 15^th and May 30^th with two row orientations (North-South: N-S and East-west: E-W) and three row spacings (45 cm, 60 cm and 75 cm) in a factorial split-plot design, replicated thrice. Growing degree days (GDD), Photo thermal units (PTU), Heliothermal units (HTU), Relative temperature disparity (RTD) and Phenothermal index (PTI) were computed using daily meteorological data. The base temperature of 10°C was used for computation of Growing Degree Days (GDD) on a daily basis. The results revealed that seed cotton yield, as well as Agrometeorological indices like accumulated growing degree days, photo thermal units, heliothermal units and relative temperature disparity were highest in crop sown on April 30^th (D₁) having maximum calendar days and reduced significantly by delay in sowing and recorded lowest values on May 30^th sown crop. Moreover, Heat use efficiency (HUE) was also found higher for early sowing and decreased subsequently by delay in sowing at both study locations. Therefore, early sowing dates are preferable than late sowing dates. Also, a significant correlation coefficient and a positive linear relation (R²= 0.942 for GDD and R²= 0.952 for PTU) were observed between various thermal indices and yield and yield attributing characters of the cotton crop, indicating a positive effect on the growth and seed cotton yield.