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Persistence of tropical forage grasses in shaded environments

Published online by Cambridge University Press:  27 March 2009

C. C. Wong  and
W. W. Stur
C. C. Wong
Affiliation:
Department of Agriculture, The University of Queensland, Brisbane, Queensland 4072, Australia
W. W. Stur
Affiliation:
Department of Agriculture, The University of Queensland, Brisbane, Queensland 4072, Australia
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Summary

The sowing of improved tropical forages in tree plantations can increase animal productivity considerably, but planted grasses often fail to persist under grazing, resulting in unstable pastures. An experiment was conducted in Brisbane, Australia during the summer of 1989/90 to investigate whether the failure of tropical grasses to persist in shade when regularly defoliated is related to their growth habit. Two shade-tolerant grasses of contrasting growth habit (prostrate Paspalum wettsteiniiv. erect Paspalum malacophyllum)were grown in simulated swards at light levels of 100, 50 and 20% of full sunlight and defoliated every 2 or 4 weeks. Shading and frequent cutting reduced total dry matter yield equally in the two grasses. Shading also reduced tiller density. Paspalum wettsteinii persisted poorly under frequent (2-weekly) defoliation in shade. Plant survival rate of this grass was 66% in the 2-weekly defoliation-20% light transmission treatment, compared with 94% in P. malacophyllum. The poor survival of P. wettsteinii was related to its high allocation of total yield to roots, low tiller density and low total nonstructural carbohydrate yield in residual biomass after defoliation. The inability of P. wettsteinii to adjust in shade to frequent defoliation led to a continual decline in photosynthetic area and light interception, resulting in the depletion of energy reserves, increased susceptibility to Rhizoctonia fungal infection and ultimately to death. It was concluded that growth habit per se cannot be used as a simple indicator for selecting tropical grasses for shaded environments. Instead, morphophysiological adaptation to defoliation in shade was critical for plant persistence.

Type
Crops and Soils
Information
The Journal of Agricultural Science , Volume 126 , Issue 2 , March 1996 , pp. 151 - 159
Copyright
Copyright © Cambridge University Press 1996

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