G.J. MANYAWU and A.U.K. MADZUDZO

Department of Research and Specialist Services, Ministry of Lands, Agriculture, and Water Development, Harare, Zimbabwe

Abstract

Three experiments were conducted to assess the feasibility of establishing irrigated Midmar ryegrass into resident grass–clover (Trifolium semipilosum) pastures, with the objective of growing a green forage for use during the dry season. Three techniques of seedbed preparation, namely: slash and leave trash (SBP 1); slash and remove trash (SBP 2); and slash, remove trash and disc (SBP 3) were tested. In Experiment 1 (1988), ryegrass was oversown into kikuyu (Pennisetum clandestinum)–clover pastures soon after imposing the seedbed treatments. In Experiments 2 and 3 (1988 and 1989, respectively), the same seedbed treatments were imposed at 3 sowing dates (early March, early April and early May) in stargrass 2 (Cynodon nlemfluensis) clover pastures. After allowing a minimum of 8 weeks for establishment, herbage was harvested. Thereafter, herbage yields, pasture botanical composition and nutritive value were measured at 4-weekly intervals. After each harvest, 40 kg/ha N was applied.
Seedbed preparation did not significantly (P > 0.05) affect total forage production in Experiment 1 and SBP 2 consistently produced the least forage in all experiments. In Experiments 2 and 3, forage yields decreased with late sowing. Significant (P < 0.05) sowing date and seedbed preparation interactions were observed. Plots prepared by SBP 3 in March had the highest forage yields. By the end of the cold season (in August), ryegrass was the dominant species in the pasture. Between August and November, plots sown in May had greater clover yields than those sown in March. Kikuyu contributed, more to total forage yield than stargrass 2.