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| Title | Water Status and Radiation Environment in Rubber (Hevea brasiliensis) Systems: A comparison between monoculture and mixed rubber-Acacia mangium plots | | Author | Ni'matul Khasanah, Thomas Wijaya, Gregoire Vincent and Meine van Noordwijk | | Year | 2006 | | Publisher | World Agroforestry Centre - ICRAF, SEA Regional Office | | City of Publication | Bogor, Indonesia | | Pages | 9 | | Call Number | PP0212-07 | | Keywords | intercrop systems, leaf water potential, light intercepted by canopy, tree growth | | Notes | In International Natural Rubber Conference 13-14 November 2006 Ho Chi Minh, Vietnam |
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| Abstract: |
| Interplanting of Acacia mangium within Hevea brasiliensis plot may be an attractive option for smallholder
rubber farmers in the tropics to increase their land productivity. Indeed, economic prospect for timber is good as
timber resource in natural forest has become severely depleted and particularly so in Sumatra where this study is
conducted.
A. mangium being a very fast growing tree species, careful timing and management of A. mangium is
probably required to reduce light competition with rubber trees. Furthermore a large portion of rubber planted
area in Indonesia is subject to two or more dry months during which rubber may shed its leaves and stops its
growth. Competition for water use between trees species in periods of low rainfall may be another constraint to
growth of the rubber tree. When soil water is gradually depleted trees can maintain their transpiration rates if they
can continue to function at more negative plant water potential. At equal rooting patterns, the trees with the
almost negative plant water potential will win the contest for remaining soil water.
This study compares a series of growth and physiological parameters measured on rubber trees grown either
in monoculture (6 x 3.3 m and 6 x 2 x 14 m) or associated with A. mangium (3 x 3 x 17 m). In the fifth year after
plot establishment, variation in the growth of rubber was analyzed in relation to leaf water potential and light
interception by canopy. Leaf water potential was used as an indicator of plant water status, but also as indicator
of competitive strength. Predawn leaf water potential of rubber trees grown in mixed systems or in monoculture
plantation did not significantly different in the beginning of dry season. However, the girth and canopy size of
rubber trees grown in mixed systems with A. mangium was significantly smaller. Leaf water potential of A.
mangium was more negative than that of rubber in the mixed system, but not as negative as that in a monoculture
of A. mangium (where A. mangium trees were competing conspecifically rather than with rubber). Better growth
of A. mangium in the mixture than in monoculture can thus have above as well as belowground explanations. The
net effect of A. mangium on depressing rubber growth, however, is likely to be primarily caused by shading. |
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