Effect of Maturity on Dry Matter Accumulation and Quality of Forage from Natural Grassland and Three Introduced Grasses in the Accra Plains, Ghana

Abstract

EFFECT OF MATURITY ON DRY MATTER ACCUMULATION AND QUALITY OF FORAGE FROM NATURAL GRASSLAND AND THREE INTRODUCED GRASSES IN THE ACCRA PLAINS, GHANA Francis Kwasivie Fianu, Supervisor: University of Guelph, 1977 Dr. J.E. Winch Two studies were conducted in Legon, Ghana, in 1974 and- 1975 to characterize the dry matter accumulation and quality of a natural grassland sward (dominated by Sporobolus and Heteropogon) and of introduced giant star grass (Cynodon plectostachyus (k . Schum) Pilger), buffel grass (Cenchrus ciliaris L. cv. biloela) and pangola grass (Digitaria decumbens Stent.). The natural grassland study was a split plot experiment with pretreatment slashing, grazing and burning in the main plots and.ten harvest dates during the major rainy season in the subplots. Each of the ten subplots was subdivided into three parts and harvested sequentially at the end of the rainy season, mid-dry season and at the end of the dry season. Pretreatments did not affect the botanical composition, dry matter accumulation during the growing season or regrowth during the ensuing dry period. Sporobolus p.yramidalis Beauv. grew faster than Heteropogon contortus (L.) Beauv. at the early stages, dominated the sward and flowered at 3-6 weeks. Heteropogon initially grew slowly and flowered from week 6. By week 7 Heteropogon became the dominant species of the sward. Cenchrus sp., Bothriochloa sp. and Setaria sp. flowered within 4-fc weeks but gamba grass (Andropogon gayanus Kunth.) did notflower during the study. Dry matter accumulation in the natural grassland sward and its dominant species continued after flowering until the end of the rainy season. Leaf production, and the In Vitro digestibility as well as nitrogen content of Sporobolus and Heteropogon were not affected by pretreatment. While Sporobolus maintained a high percentage of leaf throughout the growing season, leaf proportions dropped in Heteropogon at the mature stages. Leaves were more digestible and contained more nitrogen than stems in both species. Heteropogon tended to be more digestible than Sporobolus. The two species were similar in leaf and whole plant nitrogen, but Sporobolus stems contained more nitrogen than those of Heteropogon. In the study on introduced grasses, giant star and buffel were harvested at ten dates during the minor rainy season of 1974 (September 16 - December 3l)j during the major rainy season of 1975≫ pangola grass was included in the experiment. Pangola was sensitive to moisture stress during early growth and failed to grow during the minor rainy season of 1974* Buffel, on the other hand, was drought tolerant and grew even under light showers. Buffel flowered from week 3 in both seasons while giant star flowered only during the minor rainy season at week 6 , and pangola flowered in week 6 during the major rainy season. Growth continued in all three grasses after flowering. In buffel, senescent leaves were retained on the plant whereas in the stoloniferous grasses, they were stripped off by rainfall. During the minor rainy season, giant star and buffel produced similar dry matter yields. In the major rainy season, however, buffel was superior in yield to the prostrate grasses which showed np consistent differences. Leaf dry matter yield increased until week 8-9* Buffel and giant star produced more leaf dry matter than pangola grass. Leaf proportions in the plant declined steeply with maturity in buffel grass but slowly in the prostrate grasses. During the minor rainy season, whole plant In Vitro digestibility and nitrogen were similar in giant star and buffel during the minor rainy season, but buffel had the highest whole plant digestibility followed by pangola and giant star was the least digestible. The leaves were more digestible than stems, this difference being most striking in mature buffel grass. Leaf nitrogen levels were higher than stem nitrogen levels in all the grasses but species differences in nitrogen content were not consistent. The nitrogen content of whole plants would probably be adequate for the maintenance requirements of a steer until week 7 during the minor rainy season and week 11 in the major rainy season. In Vitro digestibility was highly correlated with nitrogen content of leaves, stems and whole plants of all species except giant star stem. It would appear that buffel grass should be harvested at 5 weeks and giant star at 7 weeks during the minor rainy season. In the major rainy season buffel would be harvested at 9 weeks and giant star and pangola at 8 weeks for optimum combination of nutrient yield during the rainy season and regrowth during the ensuing dry period. The natural grassland species and the introduced grasses were similar in digestibility at the early stages but the erect grasses -natural and introduced - declined more rapidly than the prostrate introduced ones. For high animal performance both the natural and the introduced species would have to be supplemented with concentrates.