SHADE TOLERANCE POTENTIAL OF SOME TROPICAL FORAGES FOR INTEGRATION WITH PLANTATIONS 1. GRASSES

C.C. WONG, H. RAHIM and M.A. MOHD. SHARUDIN.

Abstract

Shade tolerance of 12 tropical grasses was evaluated under artificial shade in greenhouse conditions with transmission of 64%,30%,18% and 9% photosynthetic quantum flux (PHAR) of the full sunlight followed by a field experiment to assess the performance of six selected grasses under light transmission of 100% (control) . 60%.34% and 18% of PHAR of the full sunlight and defoliated at 6- and 1O-weekly cutting intervals. In the greenhouse trial. shading significantly (P<0.01) reduced tiller production. cumulative dry matter yields of shoot. leaf, stem, stubble and root, but enhanced specific leaf area. Increased partitioning of dry matter to the leaf component at the expense of root under shade resulted in higher shoot / root and leaf /stem ratios. Mean dry matter yield reduction across the grasses were 28.7%.63.3% and 82.4% of that of the control for a 44% . 66% and 82% reduction in PHAR in the greenhouse trial. The best shade-tolerant grasses were Panicum maXimum, P. maximum cv. Tanginyika , Digitaria setivalva and Brachiaria decumbens. The least shade-tolerant species were Setaria sphacetita cv. Kazungula, Digitaria decumbens cv. Transvala and B. ruziziensis. However, at dense shade (9% PHAR transmission), the indigenous grasses, Paspalum conjugatum and Axonopus compressus were ranked seventh and fourth respectively. In the field experiment, P. maximum and B. decumbens were the best yielders across all shade levels. Mean dry matter (DM) yield reduction of the six grasses were 23.1% and 37.6% of the control for a 66% and 82% PHAR reduction in full sunlight. Axonopus compressus and P. maximum var. trichoglume produced higher DM at moderate shade under both defoliation intervals. The 10-weekly cut gave higher DM yield and tiller production under shade in the erect grasses, while the 6-weekly cut resulted in higher yield for the prostrate grasses. viz. A. compressus and p. conjugatum. Prolonged cutting intervals were preferred under heavy shade to enhance survival and botanical composition of the sown grasses. The nitrogen content of the grasses generally increased with shading and under shorter cutting interval . Low-yielding grasses, namely S, sphacelata cv. Kazungula and A. compressus, had higher nitrogen contents while P. maximum var. trichoglume had the lowest. The significance of the findings was discussed in relation to pasture management under plantations.

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