Effect of different soil fertility amendments on the nodulation and yield of two soybean varieties
Muthuri, Jacinta Karambu
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Soybean (Glycine max (L.) Merrill) is referred to as the golden crop of the future. There is a concern in Kenya on its production due to the fact that the country remains a net importer of this vital food to the tune of 100,000 tons annually yet the country has the potential to produce that capacity locally. The major impediments in local production are singled out as: Expensive farm inputs in form of fertilizers and use of inferior soybean varieties in terms of effective nodulation. The nodulation of soybean is influenced by inoculation, soil fertility, agro-ecological zones and soybean varieties. This study was carried out to achieve the following objectives, to investigate the effect of different soil fertility alteration on soybean nodulation and yield and to analyze symbiotic effectiveness between fast and slow growing rhizobia in nitrogen fixation with the soybean. Two soybean varieties (promiscuous and non-promiscuous) were planted in experimental plots at Kisii, KARI during the months of April to August 2008. There were five main treatments: Control, poultry manure, farmyard manure (FYM), di-ammonium phosphate (DAP) and inoculant strain USDA 1011. Sub-treatments were the two soybean varieties, the promiscuous variety was SB19 TGx 1740 2F while the non promiscuous was Gazelle. The experiment was carried out in a split plot design and replicated four times at Kisii, KARI Station. The greenhouse experiments were carried out to analyze the symbiotic effectiveness of fast and slow growing rhizobia isolated from Kisii while laboratory experiments were used to characterize the rhizobia isolated from the field. Nodulation status, plant biomass production, height of the plant and yield were used to generate data for the main field experiments. For greenhouse experiment, nodulation status, plant dry weight and acetylene reduction activities were used to generate the data. The transformed data was subjected to analysis of variance (ANOVA) and means were separated using Tukey’s high significant difference (HSD). The effects due to soil amendments on nodulation status were significantly different at P ≤ 0.05.There was no significant difference for grain weight for both varieties on different treatments. There was a significant difference in terms of nodule numbers and acetylene reduction assay for both soybean varieties when symbiotic effectiveness of the isolates was assessed. From the study it was concluded that the soybean treated with the inoculants had high nodulation and yield. The study also showed that FYM has slow mineralization. Fast growing rhizobia were more effective in nitrogen fixation in TGx variety than in Gazelle variety while slow growing rhizobia were more effective in Gazelle.