The effect of No3-N on Nodulation, dry matter yield and n2 fixed by Calliandra Calothyrsus
Anditi, J ANGAWA
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Calliandra calothyrsus Meissn. is a fast- growing leguminous tree which has been introduced to many tropical regions, including Kenya where it is used in agroforestry systems for fu elwood, soil improvement, reforestation and fodder production. The nitrogen fixing potential of the tree has been hampered by constraints suchas lack of compatible rhizobia in the soil, inhibitive effects of soil mineral nitrogen and unexploited host genotypic traits. Two experiments were carried out to (l) screen eleven strains of Rhizobium for N2 fixing potential in symbiotic association with C. calothyrsus and (2) assess the. influence of inorganic N03- -N on nodulation and N2 fixed by four of C. calothyrsus provenances. In experiment I, there were significant differences (p<O.05) between the Rhizobium strains on the improved growth and N2 fixed by the four of C. calothyrsus provenances. Strain effectiveness (S.E) of the eleven Rhizobium strains ranged from - 0.2% to 75.1%. Out of the three reference strains tested, only TAL 1145 gave S.E>50%. Among the strains isolated from Kenyan soils, C.C.KARJ had the highest S.E of 65.4% which was quite c10~~ to the best performing commercial strain TAL 1145 whose S.E was 75.1 %. This shows that there is a large genetic variation among Rhizobium strains which can be exploited for use in production of inoculants to improve the growth and performance of C. calothyrsus. In experiment 2, significant differences (p<O.05) were found between the provenances in shoot height, root collar diameter, root and shoot dry weights. Provenance St. Maria de Jesus from Guatemala performed best while provenance San Ramon from Nicaragua was the worst. Increasing the soil nitrogen concentration to 99 kg N03- -N ha-1 improved the plant growth significantly (p<O.05) but did not completely inhibit nodulation or nitrogen fixation, suggesting that C. calothyrsus was fairly tolerant to high soil nitrate. Therefore, the current lack of nodulation by C. calothyrsus in the soil profile under natural field conditions experienced in areas such as Embu district in Kenya may be as a result of low population or absence of effective rhizobia rather than mineral N.