Vol. 15, No. 2 GAURI et al 167 Journal of Agrometeorology 15 (2) : 167-169 (December 2013) Thermal requirement of rabi maize in North Coastal Zone of Andhra Pradesh* V. GOURI, B. BAPUJIRAO 1 , T. CHITKALA DEVI, M. B. G. S. KUMARI, and R. ANKAIAH Regional Agricultural Station, Anakapalle-531 001 1 Central Research Institute for Dryland Agriculture, Hyderabad- 500 059 E-mail: tv_gouri@rediffmail.com Short communication A range of climatic factors affect the crop growth and development. Temperature is the most important among all environmental factors that influences rate of plant growth. Grain yield of corn differs considerably across the growing areas even when soil fertility and moisture supply are near optimal. Reasons for such variation might be differences in sun shine hours or temperature etc. Temperature influences both timing and duration of the each phenophase. The effect of temperature on the length of plant growth cycle, especially the grain filling phase is the most important factor in explaining the reduced yields at warmer temperatures (White and Reynolds, 2003). The occurrence of different phenological events during crop growth period in relation to temperature can be estimated by using accumulated heat units or growing degree days (GDD). Knowledge of accumulated growing degree days can provide an estimate of harvest date as well as crop development stage (Ketring and Wheless, 1989). Heat units required for maize crop to progress from one phase to other phase has been reported earlier by Thavaprakash et al., (2007) and Girijesh et al., (2011). So a field experiment was conducted to study the thermal requirement of rabi maize in North Coastal Zone of Andhra Pradesh for ultimate planning of crop for optimized yield. Field investigation was carried out during rabi season (October - April) 2011-12 at Regional Agricultural Research Station, Anakapalle. The farm is located at an altitude of 28.62 m above mean sea level at 17°38’N latitude and 18°01’ E longitude. Daily meteorological data during crop growth period was recorded in class B observatory situated at Regional Agricultural Research Station, Anakapalle. Soil of the experimental field was sandy loam in texture, low in available nitrogen (236 kg ha -1 ), medium in phosphorus (40.4 kg ha -1 ) and high in available potassium (300 kg ha -1 ). The experiment was laid out in split-split plot design with six dates of sowing at fort nightly interval commencing from 15 th October. Sowing dates were taken as main plots, two spacings as sub plots and three nitrogen levels as sub - sub plots thus constituting 36 treatment combinations replicated three times. KH-9374 maize hybrid was sown as per the treatments and all recommended package of practices were followed. Crop protection measures were taken up against pests and disease infestation. Crop weather relations were worked out at recommended spacing and nitrogen level so as to keep the weather as the only variable in crop growth and development. Irrigations were scheduled as and when required. Crop did not suffer due to moisture stress at any stage. The dates of occurrence of silking and maturity were recorded. Grain yield was recorded after harvesting and shelling and the data was statistically analyzed. Helio thermal units (HTU) were calculated using the formula given by Rajput (1980). HTU = “GDD x Cumulative sun shine hours Phenothermal Index (PTI) was calculated as PTI = Degree days consumed between two phenological stages No. of days between two phenological stages Rate of seedling emergence Mean temperature had considerable influence on seedling emergence. Rate of seedling emergence increased from 0.08 to 0.13 per day with increase in daily mean temperature from 22.9 o C to 26.6 o C. Rate of seedling emergence was maximum at 26.6 o C and attained 50 per cent emergence within 8 days as against 15 days at daily mean temperature of 21 o C (Fig.1). Correlation studies indicated that increase in daily mean temperature significantly increased the seedling emergence (r=0.9). Sharma et al ., * Paper presented in national seminar on “Climate change and Indian Agriculture : Slicing down the Uncertainty” held at CRIDA, Hyderabad during 22-23 January-2013 and reviewed for special issue of the Journal.