Evaluation of sorghum (Sorghum bicolor (L.) Moench) Genotypes for forage quality

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Njamba, Fredrick N
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A field experiment was carried out during the 1994/95 growing season at the Zambia Seed Company (ZAMSEED) farm (located at longitude 28" 18' E and latitude 15" 19' S) to evaluate 12 selected sorghum genotypes for forage/silage yield and quality; and to determine the effect of growth stages at harvest on the yield and quality of the forage/silage. The sorghum genotypes studied were: forage sorghums (FSH-6, FSH-7, FSH-20, FSH-22, FSH-30 and FSH-57) and grain (dual purpose) sorghums (MMSH-1040, MMSH-1252, MMSH-1270, MMSH-1272, MMSH-1276 and Sima), while the growth stages were vegetative, reproductive and grain filling. A split-plot design, with 4 replications, in small plots (measuring 5m x 3m), was used, with the growth stage at harvest as main plots and sorghum genotypes as sub-plots. Traits measured included plant height (HT), leaf to stem (L:S) ratio, green forage yield (GFY), dry matter content {DM%), dry matter yield (DMY), crude protein content (CP%), crude protein yield (CRY), acid detergent fibre (ADF), acid detergent lignin (ADL) and hydrocyanic acid (HCN). The growth stages had a significant effect on all the parameters such that DM content, DM yield, ADF and ADL increased where as CP content, L:S ratio and HCN content declined with maturity. There were great variations among genotypes with respect to the traits measured except CP content of forage. It was generally observed that grain (dual) sorghums were, on average, superior to forage sorghum hybrids in most of the yield and quality characteristics studied. Interactions between sorghum genotypes and growth stage existed for most traits. Consequently, for use of sorghum as silage, most of the genotypes studied could be harvested at the grain filling (soft dough) stage to achieve high yields without adversely affecting the quality of the silage. For use as forage, however, most of the grain sorghums are better harvested at the soft dough stage, where as most of the forage sorghums should be harvested at mid flowering in order to achieve high yields while maintaining a relatively high quality. Although no single genotype was meritorious for all the parameters studied, MMSH-1276, MMSH-1040, MMSH-1252, Sima, FSH-6, FSH-20, MMSH-1270 and MMSH-1272 were found to be most promising for a good number of traits.