Peran bakteri penghasil eksopolisakarida dalam agregasi tanah tekstur berpasir

Abstract

Soil aggregation is a dynamic and very important factor for the development of agricultural soil functions. Unstable soil aggregate in a sandy soil texture becomes a limiting factor for plant growth. This research was carried out to investigate the role of a selected exopolysaccharide-producing bacterium on aggregation as well as water retention of a sandy soil texture. For these purposes, the activities conducted were : (i) isolation, selection and identification of a potential exopolysaccharide-producing bacteria, (ii) production and characterization of exopolysaccharide functional groups, (iii) determination of exopolysaccharide-producing bacteria in aggregation of a sandy soil texture, and (iv) study the impacts exopolysaccharide-producing bacteria as an active substance of soil bio-ameliorant on the growth performance of the oil palm seedlings in 61.3% sand fraction. A highly potential bacterium for exopolysaccharides production was isolated from a sandy soil located at Central Kalimantan. The bacterium was identified as Burkholderia cenocepacia KTG strain by using 16S rRNA gene sequencing. B. cenocepacia KTG strain is capable of improving aggregate stability index of a soil with 59.5% sand fraction and tolerant with low pH (3-5). Results obtained throughout this research indicate that 3% (w/v) of a 4-hydroxyphenylacetic acid or 2% (w/v) of sucrose as carbon sources yielded the higher exopolysaccharide than that of glucose, mannitol, glutamate, and lactose. IR analysis of exopolysaccharide B. cenocepacia KTG strain showed the presence of O-H (hydroxyl), C=O (carbonyl), and β glucosidic linkages as the major hydrophilic functional group of the exopolysaccharide B. cenocepacia KTG strain which noted play an important role in the sandy soil texture aggregation. Yield of dry mass of a-six-months old oil palm seedlings at main nursery was higher 1.9% (leaf), 10.5% (frond), 17.2% (stem), and 23.2% (root) by application of 75% standard dosage NPK-Mg and 100 gram bio-ameliorant/seedling than those by 100% standard dosage of NPK-Mg fertilizer. The results also showed that the B. cenocepacia KTG strain treatment caused better available water up to 11.2 – 61.6%.

Agregasi tanah bersifat dinamis dan merupakan faktor penting untuk pengembangan fungsi tanah pertanian. Ketidakstabilan agregat tanah pada tanah tekstur berpasir merupakan faktor pembatas untuk pertumbuhan tanaman. Kegiatan penelitian ini bertujuan untuk mempelajari peran bakteri penghasil eksopolisakarida potensial dalam agregasi dan retensi air pada bahan tanah tekstur berpasir. Untuk mencapai tujuan penelitian tersebut, maka kegiatan yang dilaksanakan adalah: (i) isolasi, seleksi, dan identifikasi bakteri potensial penghasil eksopolisakarida, (ii) produksi dan karakterisasi gugus fungsional eksopolisakarida, (iii) penetapan kemampuan bakteri penghasil eksopolisakarida terpilih dalam agregasi tanah tekstur berpasir, dan (iv) mempelajari pengaruh bakteri penghasil eksopolisakarida sebagai bahan aktif bioamelioran terhadap keragaan pertumbuhan bibit kelapa sawit di dalam media tanah yang mengandung 61.3% fraksi pasir. Dalam penelitian ini, bakteri potensial penghasil eksopolisakarida asal Kalimantan Tengah telah berhasil diisolasi. Identifikasi bakteri dilakukan dengan sekuensing 16S rRNA.