ABUNDANCE OF N2-FIXING RHIZOBACTERIA OF DIFFERENT DRYLAND AGRICULTURE ECOSYSTEMS IN DRY CLIMATE ZONE OF LOMBOK-INDONESIA

Abstract

Soil microbial communities are crucial in ecosystem diversity and are directly related to soil fertility. Lombok is an island in central Indonesia that has low soil fertility and a limited amount of available water. Beneficial microorganisms can be used as a low-cost and environmental friendly tool to increase productivity in dryland agriculture systems. Screening to obtain superior rhizosphere bacteria is one of the options to support the nutrient supply in arid soils. Composites soil samples were taken from five ecosystems in Lombok, West Nusa Tenggara, an arid region in the eastern part of Indonesia to obtain the isolates of nitrogen-fixer rhizobacteria (NFR). Nine Azotobacter and Azopirillium spp were isolated from, rainfed, maize, mixed crop, natural forests, and savanna ecosystems. Abundance of total bacteria and N2-fixers in all ecosystems was relatively high (more than 108 cfu g-1), and the highest total population was recorded in the natural forest. The abundance of N2-fixer rhizobacteria recorded the highest Azotobacter population at 2.64 x 108 cfu g-1 in the maize ecosystem and the highest Azospirillum population at 2.32 x 108 cfu g-1 in the natural forest ecosystem. Additionally, the highest contain of organic C and total nitrogen were obtained in natural forest and savanna ecosystem. Eighteen isolates were obtained and characterized microscopic and macroscopically, consisted of nine Azotobacter sp and nine Azospirillium isolates which are potentially to be used as biogent for improving the growth of upland rice on dry climate zone.