The aim of this study is to estimate the magnitude of GCA and heterosis for grain yield and productivity-related traits and study the influence of soil type on GCA and level of heterosis in grain sorghum. This study was carried out at the Experimental Farm of Faculty of Agriculture, Assiut University, Assiut, Egypt during 2007 and 2008 seasons. Combining ability and heterosis are important factors for efficient choice of breeding methods and parental materials in developing breeding programs to increase grain sorghum production under different types of soil. Twelve parental lines including three restorers and eight male-sterile A-lines were crossed according to linextester method to assess the combining ability and magnitude of heterosis in grain sorghum under both of clay and sandy soil. Under clay soil and surface irrigation, female line B11 and male line R-272 were the best general combiner for grain yield/plant and their GCA effects were 14.19 and 11.29, respectively, while under sandy soil and drip irrigation, the female line B93 and male line R-273 were the best general combiner for grain yield/plant and their GCA effects were 7.42 and 5.15, respectively. Heterosis results showed that male line R-273 is the best for developing sorghum hybrids under both of clay and sandy soil as heterosis for grain yield/plant in its hybrids was high under the two types of soils (101.94 and 94.18% under clay and sandy soil, respectively). However, mean heterosis of 143.90% over females line, for grain yield/plant under clay soil was obtained when male line R-272 was used as a pollinator gave the priority for this parent to be used for developing sorghum hybrids under clay soil condition. Seven and four hybrids surpassed significantly with 15 and 20% of the hybrid check cultivar (Shandaweel-6) for grain yield/plant over under both of clay and sandy soil, respectively. Most hybrids that have the line R-273 as male parent surpassed check cultivar under sandy and clay soils. Therefore, it is recommended to use that line in developing sorghum hybrids under both of clay and sandy soil.

clay soil --- Sorghum --- combining ability --- heterosis --- sandy soil

This experiment was conducted in a complete randomized block design with three treatments and four replications. Dry and fresh forage yields, starch and head contribution of plant increased with maturity. The values of ash, crude protein, pH, in vitro dry matter digestibility and leaf contribution of plant were higher (p≤0.01) in late of budding stage. The best harvest time for ensiling was late of blooming stage and before seed formation under spring condition.

in vitro digestibility --- developmental stages --- Chemical composition --- sunflower silage