Facilitation of rhizobium inoculant use by farmers in Uganda

Abstract

Short shelf-life and lack of locally available stickers are constraints to inoculant use by local farmers in Uganda. Therefore two investigations were conducted to identify a method of improving the shelf-life of Rhizobium inoculants and to obtain local inoculant stickers. Peat soil, a carrier was sterilized by autoclaving at 121oC for t hour and oven heating at 65oC for 4 days prior to incorporation of rhizobia. Bradyrhizobium japonicum inoculants were cultured and the most probable number (MPN) of rhizobia determined at 15, 60, 90 and 180 days after peat inoculation. A collection of locally available inoculant stickers namely: banana juice (undiluted) sugar solution (10%), tap water, and local gum arabic were evaluated for efficiency in gluing and protecting rhizobial cells on seed surface. Inoculants of soybean (Glycine max), Leucaena leucocephala and common beans (Phaseolus vulgaris) were used. Two best stickers were further tested for their efficiency in keeping high numbers of rhizobia on seed during 24 hours. Inoculants from unsterile and oven-sterilised peat did not maintain the recommended rhizobia population (1x108 cells gm-1) after 60 days of storage. The inoculants produced using autoclaved peat still had above the recommended rhizobial population after 6 months of storage. Banana juice and local gum Arabic significantly (P=0.05) compared well with the recommended sugar solution as stickers of rhizobia on all the types of seeds used. Water was an inferior sticker of rhizobia per seed than are recommended (108) for most of the seeds used except for groundnuts. Banana juice was significantly (P 0.05) a superior protectant of inoculants compared to sugar solution. Results suggest that autoclaving peat for inoculant production increases shelf-life of the product. While neutral banana (Mbidde) juice could recommended for use as an efficient and locally available rhizobia sticker