Reproductive Phenology and Yield Responses Of Soybean Genotypes With Varying Maturity Duration To Planting Date.

Planting date is a major factor that influences the growth, development and yield of soybean. The objective of this study was to determine the effects of planting date on the duration of the reproductive growth stages, yield and yield components of soybean cultivars differing in maturity duration. A 2-year field experiment was conducted on clay loam soils in Zambesia Province, Mozambique in 2009 and 2010 using three soybean cultivars: Storm (early maturing); Sana (medium maturing) and Olima (late maturing). Seeds were planted on four different dates at approximately 14 days interval beginning in mid-December. Split-plot design was used with planting date as main plot and cultivar as subplot. Delayed planting shortened the growing periods for each of the reproductive growth stage (R1-R8), and the decrease was more pronounced for the late maturing cultivar compared with the early cultivar. For example, averaged over cultivars, plants sown on 2 February 2010 flowered 40 after emergence (DAE) and reached physiological maturity 88 DAE, whereas those planted 49 days earlier flowered 48 DAE and reached maturity 117 DAE. In 2009, seed-fill durations (R5-R7) across cultivars decreased 8 days when planting delayed by 41 days but the declined was only 4 days when planting delayed by 49 days in 2010. Yield decreased consistently across cultivars and years when planting delayed. No interaction effect of planting date and cultivar on yield occurred. The number of pods and 100-seed weight for the early planting dates were higher than that for the late planting dates but significant interaction between planting date and cultivar occurred. Across cultivars, yields in 2009 declined by 67%, from 3.86 Mg ha^-1 for the mid December planting date to 1.27 Mg ha^-1 for the late January planting date. In 2010, yield decreased by 57%, from 4.54 Mg ha^-1 for the mid-December planting date to 1.95 Mg ha^-1 when planting delayed until early February. The results highlight the importance of early planting to achieve high soybean yields in Mozambique.