Biological nitrogen fixation of soybean in acid soils of Sumatra, Indonesia

The aim of this study is to improve soybean cultivation in transmigration areas, especially in Sitiung, West Sumatra. However, these soils are very acid, and have a high P-fixing capacity. To reduce the amounts of fertilisers, normally 5 - 7 ton lime ha ^-1 and 100 kg P as TSP, seed, pelleted with lime (60 kg ha ^-1 ) and TSP (10 kg ha ^-1 ), was introduced. In this way only 2 ton lime ha ^-1 are required.Soybean can fix nitrogen (BNF) in symbiosis with ( Brady ) Rhizobium bacteria. However, these acid soils in general, have low numbers of ( Brady ) Rhizobium . By inoculating the soils with ( Brady ) Rhizobium , BNF of soybean, and yield, were considerably improved.A study was made of the indigenous ( Brady ) Rhizobium population in view of the following:<ul><lem>Although at the beginning the numbers may be low, by repeated soybean cultivation, the numbers will increase, and they may interfere with inoculation of effective ( Brady ) Rhizobium strains.</lem><lem>These indigenous ( Brady ) Rhizobium are adapted to local stress conditions, and they may be useful for the improvement of strains, to be used as inoculants.</lem></ul>Using molecular techniques, indigenous strains derived from soil samples from old soybean areas (Java) and from new soybean areas (Sumatra) were classified in more detail. Most likely B. japonicum is the dominant strain in Java while in Sumatra B. elkanii is more present. A Sinorhizobium fredii -like strain was isolated from one soil sample from Java