This research evaluated several factors that affect plant characteristics and nutritive value of sorghum and corn silages. In Chapter II, Experiment 1 examined effects of cultivar and stage of maturity on agronomic and silage quality of forage sorghum. Experiment 2 investigated hybrid effect on agronomic and silage quality of corn. In addition to hybrid, influence of growing condition of corn was studied in Experiment 3. Effects of plant parts on forage sorghum silage digestibility and grain content on nutritive value of corn silage were studied in Chapters III and IV, respectively. Cultivar significantly affected days to half-bloom and plant height and cultivar by stage of maturity interactions occurred for whole-plant DM, whole-plant DM and grain yields, and plant part proportions in Experiment 1. The largest increase in DM content occurred from milk to late-dough for the early- and middle-season cultivars, and late-dough to hard-grain stages, for late-season cultivars. Grain yield increased significantly from milk to late-dough stages for all cultivars, and most sorghums had only slight changes at the hard-grain stage. The head part increased significantly from the milk to late-dough stages, while the other parts decreased for most cultivars. Cultivar and stage of maturity significantly affected silage CP. Silage ADF declined significantly from milk to late-dough stages for most cultivars. In Experiments 2 and 3, hybrid significantly affected days to tassel and silk. Whole-plant DM content was greatest for high grain-yielding hybrids and hybrids with drier stover. Growing condition significantly affected whole-plant DM yield, and hybrid effect was significant in Experiment 2. Variation between hybrids within growing condition occurred for whole-plant silage CP and ADF content. Stover silage CP and ADF were only affected by hybrid. Most silages with rapidly digested DM also had fast rates of ADF digestion. Extent of DM digestibility was greatest for hybrids with high grain content, and highly degradable whole-plant ADF and stover DM. Sorghum silage IVDMD was positively influenced by the head part, but negatively affected by leaf sheath in Chapter III. Intake, DM digestibility, and D-value increased linearly with increasing grain content in the whole-plant corn silages in Chapter IV.