Seed yield and its components of Brachiaria decumbens cv. Basilisk, Digitaria milanjiana cv. Jarra and Andropogon gayanus cv. Kent in north-east Thailand under different rates of nitrogen application

In a study of seed yields of pasture grasses in Thailand, pure seed yields of Brachiaria decumbens cv. Basilisk, Andropogon gayanus cv. Kent and Digitaria milanjiana cv. Jarra in one season were 81-123 kg/ha, 326-569 kg/ha and 48-97 kg/ha, respectively. Corresponding thousand-seed weights were 4.68, 3.35 and 0.42 g. Germination rates were 36, 73 and 17% at 4-6 months post harvest. In Thailand, low plant density and seeds per inflorescence, not moisture availability, are likely to be the most important factors causing low seed yields of B. decumbens. Seed production and quality of A. gayanus were exceptionally high, while seed yields of D. milanjiana were similar to reported values. The nylon gauze seed collection bags facilitated full seed retrieval. Nitrogen application increased seed yield and inflorescence density but produced significant lodging in all species at 200 kg/ha N on this sandy loam. However, it did not affect seed weight, purity, germination or viability of any of these species. Seed yields of B. decumbens in Thailand are characteristically low and present results indicate that low plant density and few seeds per inflorescence are contributing factors. The reasons for this are unknown. Gamba grass (Andropogogon gayanus), with its drought-resistant characteristics, high dry matter production, high seed production and quality and low nitrogen requirement for seed production is a useful addition to pasture options for north-east Thailand

Effect of date of closing cut on seed yield and its components of Andropogon gayanus cv. Kent

The effect of date of closing cut on seed production of Andropogon gayanus cv. Kent was studied in NE Thailand. Cutting in August, September or October produced progressively lower pure seed and pure live seed yields than the uncut control (433.9 vs 285.2, 159.3 and 62.1 kg/ha; and 302.6 vs 206.7, 99.2 and 38.6 kg/ha, respectively). Delayed peak flowering in association with increasing moisture stress, and a reduced leaf area at flowering may have led to decreased yields. Thousand-seed weight was unaffected by cutting date. Tiller density increased with later cuts, but as inflorescence density remained similar, tiller fertility decreased. Seed purity was unaffected by cutting date. Closing cuts had a large, negative effect on inflorescence size, indicated by dramatic reductions in pure seed yield per inflorescence with successive cuts. Seed germination percentage decreased following cutting in September or October, resulting in lower pure live seed yield. Closing cut dates between May and August should be investigated

Dry matter yield, forage quality and persistence of tall fescue (Festuca arundinacea) cultivars compared with perennial ryegrass (Lolium perenne) in a subtropical environment

The dry matter (DM) yield, plant persistence and forage quality of tall fescue (Festuca arundinacea) and perennial ryegrass (Lolium perenne) were compared in the subtropical environment of southern Queensland, Australia. The field study was conducted under irrigation with pure, nitrogen fertilised stands of 10 commercial tall fescue cultivars (Advance, AU Triumph, Bombina, Cajun, Dovey, Maximise, Midwin, Torpedo, Quantum and Vulcan), 3 experimental cultivars (ITF 97010, ITF 97020 and PWF 29) and Dobson perennial ryegrass. From July 1997, plots were defoliated at 4-week intervals for 3 years. Changes in crude protein content and in vitro DM digestibility (IVDMD) were determined at 1, 2, 3, 4, 6 and 8 weeks post-defoliation in October (spring) 1997, January (summer), March (autumn), June (winter) and September (spring) 1998. Some cultivars of irrigated tall fescue were shown to be better adapted to a subtropical environment than perennial ryegrass. After 3 years, cumulative DM yields were in excess of 30 t/ha for Dovey, Quantum, ITF 97010, AU Triumph and Cajun tall fescue compared with 12 t/ha from Dobson perennial ryegrass swards. Plant development had a considerable influence on crude protein content and IVDMD of tall fescue and perennial ryegrass, more so than the length of the regrowth period. As plant tissue matured, the forage quality during spring declined linearly for crude protein content and for IVDMD (1998 only), and declined exponentially for IVDMD during spring (1997), summer, autumn and winter (1998). Quality losses may be minimised if tall fescue cultivars are defoliated every 2–3 weeks during spring and summer and every 3–4 weeks during autumn and winter