Uji inokulum rhizobia dan pengaruhnya terhadap pertumbuhan Acacia mangium pada tanah masam bekas tambang

Abstract

Acacia mangium is a legume plants, which became widely known in Indonesia. This plant can make symbiosis with rhizobia to form nodules on legume crops in order to fix nitrogen for the needs of plants. In addition, it also has the ability to adapt in marginal lands, rapid growth, and good characteristhic of wood. Thus, this plant is used to fulfil the needs of industry and potential to be developed as a commodity of Industrial Timber Estates. Generaly the symbiosis between rhizobia and A. mangium can grow well only in neutral soil. However this symbiosis also has been found in acid soil and very acid soil. In this research, there were three inoculant treatments isolated from nodules of A. mangium which grown in three different places. They were KPC inoculant treatment and Kampus inoculant treatment represented acid soil, and also RR inoculant treatment represented very acid soil. Each treatment was given one ml of rhizobia inoculant. The fertilizers given were urea and KH2PO4, i.e. 0.12 g/polybag equivalent to 240 kg/ha urea and 0.08 g/polybag equivalent to 160 kg/ha KH2PO4, respectively. The plant growth media were made from the ex-mining acid soil and cow dung with ratio of 1:1 and the pH was 3.68. Analysis of variance showed that rhizobia inoculant treatment significantly increase the availability of ammonium and nitrate in the soil for all treatments. KPC inoculant treatment had the highest value of ammonium and nitrate in soil, also N plant uptake i.e. 73.1 ppm, 251.7 ppm, and 94 mg, respectively. Then, followed by RR inoculant treatment i.e. 57.4 ppm, 233.7 ppm, and 93 mg respectively. Meanwhile, RR inoculant treatment had the highest value of N-total concentration that is 2.79%. In the RR inoculant treatment occured “the concentration effect” where the N-total concentration was high but the N plant uptake was low. In the other way, KPC inoculant treatment had lower N-total concentration than RR inoculant treatment, but the plant N uptake was higher than RR inoculant treatment, this is called as “the dilution effect”. The results showed that KPC and RR inoculants treatment significantly increase dry weight of upper plant, N-total concentration, and N plant uptake. The addition of rhizobia inoculant significantly increase the value of ammonium and nitrate in soil also N-total concentration and N plant uptake in all treatments as compared with control plant.