MST-Department of Plant and Microbial Sciences

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Browsing MST-Department of Plant and Microbial Sciences by Author "Cheruiyot, R.C."

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    A comparative study of nitrogen fixation in selected cultivators of bush and climbing beans inoculated with different rhizobia strains
    (2011-12-07) Gicharu, Gibson Kamau; Mburugu, G.N.; Boga, Hamadi Iddi; Cheruiyot, R.C.
    Nitrogen deficiency is a major factor limiting bean production in Africa and Latin America. This problem can be alleviated by the use of nitrogen fertilizers which on the other hand adversely affect the environment or by the use of environmental friendly biological nitrogen fixation technology. In this study, growth experiments were designed to investigate biological nitrogen fixation in determinate (bush) and indeterminate (climbing) groups of beans. Preliminary studies on plant height and nodulation of sixty determinate and sixty indeterminate cultivars were carried out to select six cultivars for the main field study. Selected cultivars were Bush beans-Ayenew, GLP 24, Ecab 0807 and climbing beans-Cargamanto, NG224-4 and G59/1-4. Results showed that the cultivars differed statistically (P < 0.05) in both plant height and number of nodules. Greenhouse and field studies were carried out to determine the most efficient bean cultivars and rhizobia strains in nitrogen fixation. Each cultivar was inoculated with the rhizobia strains CIAT 899, USDA 2674, USDA 2676, the three rhizobia strains combined and one was not inoculated. Results from greenhouse studies showed significant statistical differences in nodulation within bush bean cultivars. The bush bean cultivar GLP24 was poorly nodulated (40.0 nodules on average) as compared to Ayenew (52.0) and Ecab 0807 (58.0) nodules. There were no significant statistical differences in nodulation among the different treatments in climbing cultivars observed in the greenhouse experiments. However, climbing beans nodulated better than the bush cultivars with NG224-4 producing 74.0 nodules on average followed by Cargamanto with 76.0 nodules and G59/1-2 the highest nodule number at 110.0. It was also observed that bush beans inoculated with USDA 2674 strain of rhizobia in the greenhouse produced the highest nodule number but in the field, it was those inoculated with strain CIAT 899. Among the climbing cultivars in the greenhouse, there were no statistical differences in nodulation between the different inoculant treatments given but in the field climbing beans inoculated with rhizobia strain USDA 2676 formed the highest nodule number. Climbing beans nodulated better than bush beans possibly because of their larger photosynthetic area, more extensive root system and the fact that their life cycle was longer. Bush beans inoculated with USDA 2674 gave the highest total plant dry weight whereas among the climbing beans those inoculated with a mixture of the three rhizobia strains gave the highest total plant dry weight. Treatments within each of the cultivars in both climbing and bush beans showed differences in total plant dry weight yield in response to rhizobia strain used. Field experiments showed that plant dry weight differed statistically between cultivars. There were no significant differences in yields between the different treatments. There is therefore need for more detailed studies to especially identify the indigenous strains of rhizobia, which in this study were found to be as effective as the recommended strains.
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    Effects of phosphorus, potassium and sulphur nutrition on nitrogen fixation of promiscuous soyabean varieties in Meru south district
    (2011-11-17) Mugendi, Njeru E.; Gitonga, Nkanata Mburugu; Cheruiyot, R.C.
    Biological nitrogen fixation (BNF) by promiscuous soybean cultivars offers a potential for minimizing the investment made by resource-limited farmers in Meru South districtKenya. Promiscuous soybean cultivars have the ability to fix nitrogen from the atmosphere if properly nodulated with rhizobia. Nitrogen fixation is influenced by factors such as availability of mineral elements and prevalent weather conditions. Nitrogen (N), Phosphorus (P) Potassium (K) and Sulphur (S) are intimately involved in plant metabolism and growth. There is, however, hardly any quantitative information on the effects of PKS fertilizer application on nodulation and nitrogen fixation of promiscuous soybeans. The objective of this study was to assess the effects of PKS fertilizer application on nodulation, nitrogen fixation and yields on promiscuous soybeans. Laboratory and field experiments were carried out to evaluate the response of promiscuous soybeans to PKS fertilizer application on both high carbon and low carbon areas. Soybean cultivars, early maturing SB19 and late maturing SB20 were the main factors while fertilizer inputs were the sub-factors. In limiting nutrient trials fertilizer inputs were 60kgP/ha+60kgK/ha+24kgS/ha, 60kgP/ha+60kgK/ha, 60kgP/ha+24kgS/ha and 60kgK/ha+24kgS/ha. For the site-specific response trials the inputs were 5kgP/ha, 10kgP/ha, 25kgP/ha and 50kgP/ha. Nodulation status, plant biomass production and yield components were used for data generation. The transformed data was subjected to analysis of variance- ANOVA using PROC GLM package to determine the main effects of the treatments and their interactions. Specific pair-wise comparisons of treatment levels were done using the least significant differences (LSD) test at P=0.05 and correlations using `PROC CORR'. In both site specific response trials and limiting nutrient trials the main effects of carbon level in the field, soybean varieties and treatments on nodulation, plant biomass production and yield components were significantly different at (P<_ 0.05). The effects due to the interaction of these factors were not significant. Field carbon level significantly (P<_ 0.05) influenced nodulation, plant biomass and the yield components across the two soybean varieties. Application of varying amounts of P fertilizer and application of PKS fertilizers significantly (P<_ 0.05) influenced nodulation, plant biomass production and the yield components. Varietal differences significantly influenced plant biomass production and yield components but did not significantly influence nodulation. Laboratory and greenhouse results indicated that the isolates obtained were slow growing Bradyrhizobium japonicum, Bradyrhizobium elkanii and the fast growing Sinorhizobium fredii.