Yield and its attributes as affected by planting dates in soybean (Glycinemax) varieties

A field study was conducted for 2 years during 1992-93 to find out the geno typic response in terms of yield and its attributes and to assess the suita bility of varieties under varying planting dates. The experiment comprised of 5 planting dates and 12 predominant soybean (Glycine mm (L.) Merr.) vari eties. Significant differences were obtained for yield and most of the yiel d attributes among planting dates and among varieties. Early planting by 20 June was found to be the most appropriate for high seed yield (1 666 kg/ha ) across years and varieties. In subsequent plantings of 30 June; 10, 20 an d 30 July, there were yield reduction of 4.8, 8.5, 28.1 and 39.7% respectiv ely. Suitable soybean varieties, viz 'JS 335','NRC 2' and 'JS 71-05' were i dentified to give high soybean yield across all planting dates and years. T he reduction in seed yield due to late plantings was mainly due to the comb ined effect of reduced total biomas, pods/plants, plant height, number of b ranches, 100 seed weight, days to flowering and days to maturity.