Diagnosis faktor penghambat pertumbuhan akar sengon (Paraserianthes falcataria L. Nielsen) pada Ultisol di Lampung Utara

Due to wide-scale deforestation and their need for forest products smallholder farmers in North Lampung are becoming interested in tree farming. Farmers often cultivate a mix of fruit spice and fast-growing timber species. Paraserianthes falcataria (sengon) is the most common timber tree in the area. This species demonstrates inconsistent performance growing particularly poorly on ridges. Poor performance might be due to poor root development resulting from deficient soil conditions. Inhibition of root growth on acid soil is usually linked to Al toxicity but other soil characteristics such as low P availability or soil physical factors (such as mechanical impedance or poor aeration) might be involved as well. The objective of this study was to diagnose the soil factor(s) that limit(s) the growth of Paraserianthes on ultisol in North Lampung. Measurements of soil bulk densities at different soil depths in Ultisol are difficult to interpret because clay content tends to increase with depth. This difficulty was addressed by correcting soil bulk density (BD) by using a ‘pedo transfer function’ based on clay and silt content. The resultant BDref value makes it possible to compare soils of different textures (soil depths). The results shows that the 5 year-old Paraserianthes developed a shallow root system with about 50% of main root growing horizontally in the upper 0-30 cm of the soil. No significant correlation was found between root length density (Lrv) and the concentration of exchangeable Al or monomeric Al. Poor root growth at greater soil depth (40- 70 cm and 70-100 cm) was significantly correlated (p1.14. The data also suggests lower BD/BDref values and better root growth for microsites with higher soil organic matter as indicated by C-org/Cref. The BD/BDref ratio can be used as a tool to diagnose poor root growth on Ultisol in North Lampung.

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