RESPONSE OF SOYBEAN YIELD TO LATE SOWING DATES

This work conducted on the research farm of Mallawi Agricultural Research Station, El-Minia Province, Egypt, during two successive seasons of 2004 and 2005 to study the role of the late plant-ings on the productivity of soybean. Three out of four genotypes selected to achieve that goal were new released cultivars, Giza-22; Giza-35; and Gi-za-111, and the commercial one, Crawford, the common parent of the three genotypes, as control. Three planting dates started on June 1st, June 15th for the second date of sowing and ended on June 30th for the third sowing date in both seasons. The package of the recommendations of soybean cul-ture carefully applied to get the best results of each sowing date. The results showed that all of the morphological, yield and productivity traits highly significantly affected by genotype and three out of five morphological traits, number of days to both flowering and maturity and plant height, also high-ly significantly affected by late sowing date. The other two traits, number of branches and leaf area at 75 days just significantly affected by late sow-ing date. In terms of yield and its components traits, only seed index highly significantly affected by late sowing date and yield per plot significantly affected by sowing time. All productivity traits were significantly affected by late sowing date specially the content of both oil and protein. Alt-hough yield per plot was significantly affected by late sowing date, the yield per plant was not af-fected by late sowing date indicating that the fac-tor of time of sowing may affect the rate of the germination and control the stand of the plots. Number of active nodules considered as produc-tivity trait because of the residual nitrogen that remain in the soil after harvest for the next crop. This number was significantly affected by sowing time and reached the highest values in the second date of June 15th that may due to the high tempera-ture at this time which lead to increasing the inter-action between soybean roots and the nodule bac-teria.