Tropical Grasslands (2007) Volume 41, 35–42

Seed production of two brachiaria hybrid cultivars in north-east Thailand. 2. Closing date defoliation

M.D. HARE, P. TATSAPONG AND K. SAIPRASET

Faculty of Agriculture, Ubon Ratchathani University, Ubon Ratchathani, Thailand

Abstract

Two field trials were conducted during 2003–2004 in north-east Thailand to examine the effects of timing of closing defoliation on: seed production; forage production before closing to seed; and yield and quality of stubble at seed harvest of 2 brachiaria hybrid cultivars, Mulato (Brachiaria ruziziensis x B. brizantha) and Mulato II (B. ruziziensis x B. decumbens x B. brizantha).
In Trial 1, second- and third-year Mulato seed crops closed in early July and early August produced more seed than crops closed in May and September.
In Trial 2, seed yields of first-year Mulato seed crops closed in September were reduced by over 50% relative to crops closed in May–August. Seed yields of first-year Mulato II seed crops were reduced by 70% when closed in August rather than May or July, and September closing produced no seed at all. The highest seed yield of Mulato II (258 kg/ha) was 60% higher than the highest seed yield of Mulato (161 kg/ha), mainly because it produced nearly twice the number of pure seeds/m2.
From the results of our research, we would recommend a final closing defoliation for brachiaria hybrid cultivars in Thailand any time in July.
Forage production before closing to seed was significantly higher in late-closed seed crops than in early-closed seed crops. In contrast, stubble DM yields at seed harvest increased progressively as the date of closing was advanced earlier into the wet season.
The difficulties of implementing closing defoliations by smallholder seed producers and the methods of harvesting are discussed.

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