Rhizobium inoculation and sulphur fertilizer improved yield, nutrients uptake and protein quality of soybean (Glysine max L.) varieties on Nitisols of Assosa area, Western Ethiopia

A greenhouse experiment was conducted to study the effect of inoculation of Rhizobium strain and sulphur fertilization on seed and straw yields, nutrients uptake and seedquality protein of two soybean (Glysine max L.) varieties. The experiment consisted of four levels of S (0, 20, 30 and 40 kgha-1), three Rhizobium strains (MAR-1495, SB-6-1-A2and TAL-379) and two soybean varieties (Belessa-95 and Wollo) combined factorially in complete randomized design (CRD) with three replications. Grain and straw yield and nutrients uptake increased by inoculation of Rhizobium strain whether used alone or in combination with S. Application of strain and S further increased seed and straw yield and nutrients uptake. Seed yields of Bellessa-95 inoculated with MAR-1495 at 30 and 40 kg S ha-1 were estimated to be 3864.1 and 3893.8 kg ha-1, corresponding to 112 and 114%  increase; but Wollo was with seed yields of 3633.3 and 3709.2 kg ha-1, corresponding to 160 and 166% increase, respectively over control. Estimated soil N balance was maximum for S application along with inoculation of strains, ranged from -29.25 kg ha-1 in control to 80.74 kg ha-1 for Bellessa-95 and from -21.76 kg ha-1 to 84.66 kg N ha–1 for Wollo, respectively. Efficient seed nutrients uptake due to combined application further caused significant (p<0.001) increase in protein yield of soybean. With strain MAR-1495 protein yield varied from 26% in the control to 41.5% for Belessa-95 at 30 kg S ha–1, while from 28% in the control to 44% for Wollo at 40 kg S ha–1, respectively. The results clearly suggested that balanced application of S along with Rhizobium strain can affect grain and straw yield and nutrients uptake of soybean varieties, enhance their growth and improve grain quality protein as well as benefit on soil N balance in S-deficient soils.   Key words: Sulphur, strain, nutrients use efficiency, quality protein, soil nitrogen balance.