Potensial air daun dan efisiensi penggunaan cahaya dalam sistem karet (Hevea brasiliensis) monkultur dan karet campuran dengan akasia (Acacia mangium)

Interplanting of Acacia mangium within rubber (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. Light competition with rubber trees may occur as A. mangium being a very fast growing tree species. Thus, careful planting 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, water competition may occur in such condition. Co mpetition for water use between tree species in periods of low rainfall may be another constr aint to growth of the rubber tree. In other word, light and water competition are two forms of competition which can not be prevented in having mixed systems of H. brasiliensis – A. mangium. This study compares a series of growth response, either morphological or physiological parameters measured on rubber trees grown either in monoculture (6 x 3.3 m and 6 x 2 x 14 m) or mixed with A. mangium (3 x 3 x 17 m). In the fifth year after plot establishment, variation in the growth of r ubber was analyzed in relation to leaf water potential (LWP), light interception by canopy and light use efficiency (LUE). LWP was used as an indicator of plant water status, but also as indicator of competitive strength. Predawn LWP of rubber shows significant differences between rainy and dry season. LWP of A. mangium is much lower than rubber. However, LWP of rubber under different systems studied does not show any consistent difference. On the other hand, even though the LUE of rubber trees in mixed systems with A. mangium does not show significant different compare to monoculture systems, but the biomass and light intercepted of rubber trees in mixed systems with A. mangium was significantly smaller compare to monoculture systems. Thus, the net effect of A. mangium on depressing rubber growth is likely to be primarily caused by shading. Result of WaNuLCAS model simulation shows that management option to have delay of planting of A.mangium to the planting of H. brasiliensis shows significantly effect on the growth of H. Brasiliensis . If delay of planting of A.mangium reaches 5 years, year of tapping of H. brasiliensis almost the same to the monoculture systems. Planting A. mangium on the same year with H. brasiliensis or having delay of planting of A.mangium less than 5 years should be follows by harvesting of A. mangium . The longer delay of planting of A.mangium , the faster H. brasiliensis reach year of tapping but the longer year of harvesting A. mangium

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