Phenological development of grain sorghum as affected by planting date

Abstract

Phenological development of grain sorghum [Sorghum bicolor (L.) Moench] is a direct result of accumulated heat units (growing degree days) from emergence to physiological maturity. This study was conducted in 1994 and 1995 to determine the effect of planting date on the phenological development of six grain sorghum genotypes grown in the Brazos Bottom (Burleson County), near College Station, Texas. The grain sorghum genotypes consisted of two medium-early, two medium, and two medium-late maturity classes. Experimental design was a randomized complete block utilizing split plots with eight replications. Main plots consisted of an early and late planting date, and subplots consisted of the six genotypes. Data collected was represented as the number of days and growing degree days (base temperature = 7 o7) from emergence to each of nine phonological stages. Average number of days and growing degree days (GDD) to each phenological stage of development throughout this study were significantly affected by the interactions of genotype x planting date, genotype x year, planting date x year, and genotype x planting date x year. These interactions were due to the individual and combined response of the genotypes to the differences in growing conditions between the early and late planting dates and years. Average number of days from emergence to each phenological stage of development decreased as planting was delayed. On average, number of days at the late planting from emergence to floral initiation (stage 3), anthesis (stage 6), and physiological maturity (stage 9) were reduced 15.5, 11.8, and 8.4%, respectively. Accumulated GDD to each stage of development showed mixed results between 1994 and 1995. The late planting in 1994 required more GDD, while in 1995 the early planting required more GDD to reach a specific stage of development. Yields and yield components showed no specific response to planting date. This lack of response was probably due to the abbreviated time (I 3 days) between planting dates.