Studies on Wild Sorghum (Sorghum Arundinaceum) as Silage Material

Abstract

Three experiments were carried out at the Department of Animal Science, University of Ghana, Legon on the Accra plains between January and November, 1990 to examine a) the factors influencing germination of "wild sorghum" (Sorahum arundj.naceum) seeds b) changes in the dry matter yield and nutrient composition of "wild sorghum" with growth c) the effect of treatment and duration of preservation on the quality of "wild sorghum" silage. Seeds of "wild sorghum" were used in establishing the field in Experiment 1. Seeds were collected at 3, 4, 5, 6, 7 and 8 weeks after inflorescence appearance and used for the germination test. For each of the seed sample collected, four scarification treatments, namely, mechanical, acid, hot water and dry heat were used. High germination rates were obtained for seeds collected between four and five weeks after inflorescence appearance and mechanical scarification was the only treatment which improved germination in this experiment. The germination obtained were 67.5% and 57.0% with seed harvested at four and five weeks after inflorescence appearance compared with the control which gave values of 47.5% and 27.5% respectively. In Experiment 2, the plants were harvested beginning at six weeks post-planting and continued at two weeks intervals until the fourteenth week, DMY of the whole plant significantly increased (p<0.01) with increasing maturity reaching 10.18 tha'1 in the fourteenth week. The proportions of dead leaves, stems and inflorescence stalk increased while the percentages of green leaves and leaf sheaths decreased with advancing growth (p<0.01). Crude protein content in the whole forage and those of the yarious morphological fractions decreased (p<0.05) with maturity. Cell wall constituents of the whole forage and those of the various fractions increased (p<0.01) with advancing growth period. IVDMD of the whole forage and the morphological fractions also decreased (P<0.05) with advancing growth. HCN content of the whole forage decreased (P<0.05) with advancing growth from an initial value of 530 mg kg"1 (Dm) to 222mg kg'1 (Dm) at the final harvest. In Experiment 3, stem cuttings of "wild sorghum" collected from University of Ghana farms, Legon, were used in establishing the field. The regrowths ie. both secondary and tertiary growth were used for the ensilage. Herbage in both cases were harvested after ten weeks of regrowth. The harvested herbage were chopped to 2-3cm lengths for ensiling. Polyethylene bags were used as silos, each of the silos was then filled with one kilogram of the Sorghum for one of four treatments of the chopped herbage ie. (i) sorghum with nothing added (ii) sorghum with 0.5% formic acid (iii) sorghum with nothing added but wilted in the sun for six hours (iv) sorghum combined with Leucaena leucoceohala (leucaena) in the ratio of 7:3 and were duplicated. The materials were ensiled over a period of 28, 56, 84 and 112 days. DMY of secondary and tertiary growths were 9.71 and 10.07 t ha'1- Ensilage was generally good for all treatments. There was not much change in the silage quality within the four month ensiling period. Crude protein content did not change but ammonia nitrogen content increased with ensiling period. Both pH and the total volatile fatty acids (TVFA) increased with increasing ensiling period. Of the cell wall constituents only NDF significantly (P<0.05) decreased with ensiling period whereas the rest did not show any significant difference . IVDMD decrease with ensiling period. The use of formic acid as an additive improved the silage quality. Wilting increased the dry matter content. The inclusion of the legume leucaena to the "wild sorghum" at 30% increased the crude protein content from 6.12% to 24.01% and IVDMD from 47.17% to 59.55%. The legume inclusion also decreased the NDF content from 77.76% to 66.89%, ADF from 47.40% to 33.47%, cellulose from 36.27% to 25.81%, ADL content from 6.97% to 6.21% and HCN content from 354.8 to 252.0 mg (DM) Kg"1. However there was not much difference in silage quality between "wild sorghum" combined with leucaena and other treatments.