Tropical Grasslands (1985) Volume 19, 81–87

GROWTH, CANOPY STRUCTURE AND CHEMICAL COMPOSITION OF LABLAB PURPUREUS CV. RONGAI AT SAMFORD, S.E. QUEENSLAND

R.E. HENDRICKSEN and D.J. MINSON

CSIRO, Division of Tropical Crops and Pastures, 306 Carmody Road, St. Lucia, Qld. 4067

Abstract

Growth, canopy structure and nutritive value of Lablab purpureus cv. Rongai were measured during summer and autumn in south-east Queensland.
Dry matter (DM) accumulated at rates ranging from 10 to 83 kg ha-1 d-1. The maximum DM yield was 6270 kg ha-1 at 121 days of age and green leaf comprised 30–40%. of the green DM yield 100 days after sowing. Fifty percent of this green leaf was in the layer 30–60 cm above the soil surface and had a bulk density of 23–31 kg DM ha-1 cm-1.
The in vitro digestibility of green leaf was 67.5% (range 55.3%–74. 1%) and of green stem was 45.7% (range 37.4%–72.2%) The digestibilities of leaf and stem in the top canopy layers (30–75 cm) were higher than in the bottom layer (0–30 cm) and declined with maturity in all but the top (60–75 cm) layer. The average rate of decline per day was 0.06% units and 0.11% units for leaf and stem respectively.
Nitrogen, potassium and phosphorus content of the leaves increased with canopy height whereas the calcium, molybdenum, manganese and zinc content decreased.
It was concluded that the DM yield, nutrient concentration and digestibility of leafy herbage in the top half of a Rongai canopy are sufficient to sustain medium levels of animal production provided the animals are able to graze selectively.

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