Abstract

The use of biofertilizers and organic matter can eventually reduce the need for inorganic synthetic fertilizers which are potentially more detrimental to the environment. The objective of this work was to study the impact of soil inoculation with Rhodotorula mucilaginosa MB151 and Saccharomyces cerevisiae 66 in a soil inoculated with Bradyrhizobium japonicum 110 and amended with different concentrations of humic acid (HA) or fertilized with full dose of N (nitrogen), P (phosphorus) and K (potassium) as full NPK control on soybean growth and productivity. Field inoculation experiments were carried out during two successive seasons in a sandyloamy soil. The total microbial count, the physiological and the yield parameters of soybean were determined. The two yeast strains produce indole acetic acid and gibberellins. All the growth parameters of soybean were significantly enhanced due to application of yeasts, especially S. cerevisiae. The treatment T11 (S. cerevisiae + 3% HA) gave the significantly highest increase in N% and consequently the crude protein percent (6.37, 6.43; 39.81, 40.19) of soybean seeds at both seasons respectively. The soybean seeds oil percent increased as the HA% increased in the different treatments during the first season in comparison with control T1 (full NPK). The treatments T12 (S. cerevisiae + 4% humic acid) and T13 (S. cerevisiae + 5% humic acid) gave increase in seeds oil % equal 1.2 times the control T1. T11 (S. cerevisiae + 3% HA) gave significant increase in seed yield and straw yield (3.816 and 3.838; 5.377 and 5.380 Mg.ha¹) during the two seasons, respectively. It could be concluded that application of yeasts in soil amendment with HA, through the numerous direct or indirect mechanisms of action, allow significant enhancement in soybean growth and productivity.

Key words: Organic matter, Rhodotorula mucilaginosa, Saccharomyces cerevisiae, Bradyrhizobium japonicum, soybean.