Pengaruh Tegakan Mahoni (Swietenia macrophylla King) Terhadap Pertumbuhan dan Produksi Jarak Pagar (Jatropha curcas Linn.)
The Influence of the Mahogany Stands (Swietenia macrophylla King.) On The Growth and Production of Jatropha curcas (Jatropha curcas Linn.)
Agroforestry of mahogany and jatropha in Babakan Madang RPH was established. Jatropha were planted under mahogany stands of 3 years old (young mahogany stands), and 17 years (old mahogany stands). The difference of ages of mahogany may give influence on the growth and production of jatropha. The purpose of this research was to determine the influence of the mahogany stands (S. macrophylla) on the growth and seed production of Jatropha (J. curcas).
The growth parameters of jatropha consisting of height, diameter, length, width tree crown were measured. These growth parameters were used to determine the tree crown width, as well as root length. Jatropha curcas plant height measurement was done by using graft-scale, while for measuring the widht, length and width of the crown, band meter was used. In this case, census method was applied. In every mahogany stand, 15 J. curcas trees were chosen for sampling. Root length of jatropha was measured by digging method. Horizontal and vertical roots were measured.
The result showed that the growth of jatropha was significantly affected by the stand age of mahogany. Young mahogany stands produced better effect on height, diameter, length, width, and crown width of Jatropha than in old mahogany stnads. It was also strengthen by the results of the t-test (p<0.05) that diameter, height, and crown width was affected by mahogany stand. The average diameter of the jatropha planted under young mahogany stand (JPYMS) was bigger (2,3 cm) then jatropha planted under old mahogany stands (JPOMS) which is 1,8 cm. The average height of jatropha under JPYMS was 142,2 cm, while average height under JPOMS was 125,4 cm only. While, crown width under JPYSM was larger (31,4 cm) than crown width under JPOMS (21 cm). Production of JPYSM was also better than the JPOMS. Seed production in JPYMS was 21 g, whereas the JPOMS was 7,47 g.
The root was also measured as one of growth variables. However, according to the result of t-test, the root length at
horizontal distribution was not significantly different compared to roots at vertical distribution. The average value of vertical root of jatropha ranged from 19,5 cm to 20,8 cm while horizontal root ranged from 64,2 cm-55,6 cm. This difference was caused by low nitrogen content, in addition its soil structure was clay structure. Therefore, there were some mechanical obstacles of the land for root development. Root length in jatropha can be used as optimal range of planting distance in agroforestry system. In conclusion, the growth of jatropha under young mahogany stands was better than in old mahogany stands, especially on growth parameter of diameter, height, length, crown width, and seed production. There was no influence of mahogany stands to horizontal and vertical jatropha’s root length. Jatropha can be used as intercropping crop if the light intensity is sufficient, and maintain intensively. The appropriate planting distance under forest stand is 2 m x 2 m.