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

Abstract

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.