Effects Of Rhizobia Inoculation And Phosphorus Levels On Soybean (Glycine Max L.Merril) Yields And Selected Soil Properties In Embu County, Kenya

ABSTRACT

Soybean (Glycine max L. Merril) productivity in Kenya is adversely affected by low yield, poor fertilizer use, ineffective inoculation, and soil fertility management constraints. The empirical understanding of the interaction between native soil rhizobia, inoculation, nitrogen fixation, soil fertility management practices and how these factors influence soybean productivity is insufficient. The general objective of this study was to investigate the effect of rhizobium inoculation and P fertilizer on nodulation and soybean yield on smallholder farms in Embu County, Kenya. Three P-fertilizer rates were evaluated with or without rhizobia inoculation in a randomized complete block design (RCBD) with six replicates. The P-Fertilizer rates included 0, 30 and 60 kg P ha-1 . Soils were sampled thrice; before experimentation and after harvesting in 2 seasons (SR 2012-Oct, Nov, Dec; LR 2013-Mar, Apr, May). Nodulation was determined at 50% flowering (40 days after emergence -DAE) while biomass (above and below ground) was measured both at 50% flowering and at physiological maturity. Phosphorus use efficiency (PUE) was determined as a ratio of yield and P fertilizer input while grain yield was extrapolated from plot quadrats after moisture correction. Data was recorded and subjected to analysis of variance (ANOVA) and means separated by the least significance difference (LSD) at P≤ 0.05. Paired t-test was used to compare soil chemical properties before and after the experiment. The results indicated a significant yield increase in fields with rhizobial inoculation and application of 60 kg P ha-1 compared with the control treatment Total stover weight, number of nodules, total dry matter (DM) (shoot dry weight+root dry weight) and grain yield were significantly higher (p