Pengaruh Legum Penutup Tanah Terdapat Pertumbuhan Semai Mahoni (swietenia macrophylla) pada Tanah Marginal

Indonesia has large area of marginal land including coast sandy soil and post coal mining soil areas. Reclamation process for marginal land needs long time and high cost, hence, strategic treatments are necessary to reduce both time and cost. This research aims to analyze the effects of media (coast sandy soil, alluvial deposit, and post coal mining soil) and legume over crop Centrocema pubescens on the growth of mahogany seedlings. This research was conducted at green house for 3 months using Completely Randomized Design (CRD) with 3 x 2 factorials and 3 replications. The first factor was marginal soil (three levels: coast sandy soil, post coal mining soil, and alluvial deposit as reference) while the second factor was the application of legume cover crop (two levels: apply and not apply). Variables observed were the height, diameter, biomass, and nutrient content of mahogany seedlings. The results showed that the growth of mahogany in sandy soil media is the best though nutrient content in that media is the lowest. It was caused reduction of salinity from that media. While, up to 3 months old, C. pubescens grew competitively.

The Identification of Land Subsidance by Levelling Measurement and GPR Data at Tanjung Emas Harbour, Semarang

Recently, the main problem in Semarang City is flood. This area has low relief that consists of coastal alluvial deposits, swamp and marine sediments. The coastline is characterized by muddy, sandy, and rocky coasts, and mangrove coast. Ground Penetrating Radar (GPR) records, show that subsurface geological condition of northern part of Semarang is coastal alluvial deposit and in the south is volcanic rocks. The aims of this this research is to determine land subsidence by levelling measurement in 2005 in Tanjung Emas Harbour area built on 1995. During ten years, there are various land subsidance in this area: in Coaster Street (21 – 41 cm), container wharf (62 – 94 cm), north breakwater (64 – 79 cm), west breakwater (74 – 140 cm), east groin (76 – 89 cm), and stacking area ( 77 – 109 cm). According to this research, it is concluded that one reason causes of flooding in this area is land subsidence.Keywords : flood, land subsidence, levelling, Tanjung Emas Harbour, Semarang Permasalahan yang berkembang di Kota Semarang saat ini adalah terjadinya banjir. Kawasan ini berelief rendah yang disusun oleh endapan aluvial pantai, rawa dan sedimen laut. Karakteristik garis pantai dicirikan oleh pantai berlumpur, berpasir dan berbatuan, serta pantai berbakau. Rekaman Ground Penetrating Radar (GPR) menunjukkan kondisi geologi bawah permukaan utara kota Semarang merupakan endapan aluvial pantai dan bagian selatan disusun oleh batuan vulkanik. Tujuan penelitian ini adalah untuk mengetahui kondisi penurunan tanah melalui pengukuran sifatdatar yang dilakukan pada tahun 2005, di kawasan Pelabuhan Tanjung Emas yang dibangun pada tahun 1995. Dalam kurun waktu 10 tahun, diketahui bahwa terdapat variasi penurunan tanah di kawasan ini: ruas jalan Coaster (21-41 cm), di kawasan dermaga peti kemas (62-94 cm), pemecah gelombang sebelah utara (64-79 cm), pemecah gelombang sebelah barat (74-140 cm), penahan gelombang sebelah timur (76-89 cm), dan pelataran peti kemas (77-109 cm). Berdasarkan penelitian ini, maka dapat disimpulkan bahwa salahsatu penyebab banjir di kawasan ini adalah akibat penurunan tanah.Kata Kunci : banjir, penurunan tanah, sipatdatar, Pelabuhan Tanjung Emas, Semarang