Selection of efficient Bradyrhizobium isolates to use as biofertilizer for cultivation of indigo Undigofera tinctoria L.)

Abstract

This research was conducted over the period from 2004 to 2007 to achieve the ultimate objective of preparation and use of peat-based efficient Bradyrhizobium inoculants as biofertilizer for cultivation of indigo in Bangladesh. For isolation of Bradyrhizobium, root nodules of indigo Undigofera tinctoria L.) were collected from indigo growing areas, two from Rangpur and one from Nilphamary districts. Fourteen Bradyrhizobium isolates were identified depending on colony, morphological and biochemical characteristics. Of the 14 isolates, six were found promising with respect to nodulation, shoot weight and N uptake of indigo plants grown inside the Leonard Bottle Jar Assembly (LBJA). Peat-based Bradyrhizobium inoculants were prepared with the six isolates and the inoculants were tested for their effects on nodulation, growth and yield of indigo plants through a pot and a field experiment in 2005. Three isolates viz. HSTU-IR3. HSTU-IR, and HSTU-IR, showed better performances and their inoculants were prepared for field trials. Field trials were conducted for two consecutive years (2006 and 2007) with 11 treatments (control, 3 inoculants, 3 inoculants + 20 kg N ha’! as urea, 3 inoculants + 40 kg N ha’ as urea and 60 kg N ha’‘as urea). In both years, the highest nodulation, seed yield, hay yield, stubble yield and the highest NPKS uptake were recorded with the HSTU-IR; inoculants +20 kg N ha’'as urea treatment. Application of 40 kg N ha’ as urea exerted negative effect on the effectiveness of Bradyrhizobium inoculants in indigo cultivation. A pot experiment was also conducted with indigo green manuring in tobacco crop. It reduced the incidence of root-knot disease of tobacco and thereby increased the crop yield. This study has practical implications to soil fertility management which would create significant impact on sustainable crop production.