Effects of dual inoculation with mycorrhiza and rhizobium on growth performance of soyabeans in acidic soils in Gatanga Kenya

Abstract

Small land holdings and poverty in Central Kenya have made it difficult for farmers to adequately conserve and replenish soil nutrients in their farms. Soil erosion and leaching of nutrients leading to soil acidity have been the inevitable outcome. This study was designed to determine the effect of inoculating soyabeans (Glycine max) with both mycorrhiza and rhizobium as a biological means of improving soil fertility in the acidic soils in Gatanga, Thika District. Field experiments were carried out in Gatanga and at Kenyatta University (on-station) in sterilized and non-sterilized soils collected from Gatanga. The field experiments were laid out in complete randomized block design while the on-station ones were laid out in complete randomized design. Analysis of variance (ANOVA) was conducted on the data and means separated using LSD at 5% significance difference using Genstat for Windows Version 8.11. The growth parameters; height, root collar diameter, shoots and root dry weight all increased as a result of dual inoculation with mycorrhiza and rhizobium. Dual inoculation also led to increased nitrogen fixation by soyabeans, evidenced by increased nodulation, and grain yields. Dual inoculation with mycorrhiza and rhizobium did not have any significant effect (p<0.05) on germination of soyabeans. Height of soyabeans as a result of dual inoculation increased significantly over the control by 88% in the long rains while in the short rains the increment was not significant. In the on-station experiments, height increment over the control in sterilized and non-sterilized soil was not significant. Dual inoculation increased root collar diameter by 80% and 8.6% in the long and short rains respectively. Shoots dry weight in the on-farm long rains 2005 season increased byl40% as a result of dual inoculation while in the short rains season and the on-station experiments, the differences were not significant. Dual inoculation increased grain yields by 356% in the on-farm long rains 2005 season, while in the on-station experiments grain yield increased by 76% and 107% in the sterilized and non-sterilized soils respectively. Though nodulation was poor in all the experiments, the number of nodules increased significantly by 676% over the control in the long rains 2005 season. In the on-station experiments the control (S) had no nodules. The short rains crop performed poorer than the long rains crop as a result of insufficient rains. In conclusion, the biological organisms; mycorrhiza and rhizobium, could be utilized to increase productivity of the legume soyabean, in acidic soils. However, technologies to avail the microorganisms to the farmers need to be developed as the obligate nature of mycorrhizal fungi makes it difficult to culture and commercialize while the low shelf life of rhizobium at room temperature is a hindrance for its use by resource poor farmers