Growth And Nodulation Of Some Multipurpose Nitrogen Fixing Trees In Two Tropical Soils

Abstract

The aims of the study were to investigate nodulation of four tree species namely Leucaena leucocephala, Leucaena diversifolia, Calliandra cel.ot.trisyas and Sesbania sesban in various ecological zones of the country. During the study Rhizobium bacteria were isolated from nodules of the four tree legumes, characterized and screened for their nitrogen fixing potential in potted field soils. Among the Rhizobium isolates 16, 14, 10 and 18 cultures were authenticated as Rhizobium strains for L. leucocephala, L. diversifolia, C. calothyrsus and S. sesban respectively. All the isolates gave an acid reaction in a yeast extract mannitol agarbrornothymol blue medium indicating they were of the fast growing type. However, the Rhizobium isolates varied considerably in their compatibility with the four tree species. All the 30 Leucaena isolates cross-nodulated both Leucaena spp. and C. calothyrsus seedlings but only 17 of the isolates cross-nodulated

S. sesban. Among 10 C. calothyrsus isolates, 6 cross-nodulated L. diversifolia and 5_ sesban while 4 cross-nodulated L. diversifolia and S. sesban while. 4 cross-nodulated' L. leucocephala. From a total of 18 S. sesban isolates, 9, 11 and 7 Rhizobium isolates cross-nodulated .1. leucocephala, L . diversifolia and C. calothyrsus respectively. However, all the isolates nodulated their respective hosts.

Relative effectiveness varied from one isolate to the other. Inoculation of the tree species in vermiculite using Rhizobium isolates resulted in shoot dry matter increases ranging between 34.3 - 102.9%, 16 - 56%, 0 - 25% and 0 - 186% for L. leucocephala, L diversifolia, C. calothyrsus and S. sesban respectively over the uninoculated treatments. Correlation between shoot dry weight and nodule dry weight was significant at 5% probability level in L. diversifolia (r = 0.703) and S. sesban (r = 0.614) but was not significant in the case of L. leucocephala (r o . 578 ) and C. calothyrsus (r = 0.409). In both the Kibwezi and Kabete soils used in this study the control plants in uninoculated treatments nodulated except L. leucocephala in the Kabete soil. Inoculation of the tree species using Rhizobium strains resulted in shoot dry weight increases ranging between 0 - 89%, 0 - 14%, 0 - 169.7% and 0 -86.8% for L.

leucocephala, L. diversifolia, s. sesban and C. calothyrsus respectively over the uninoculated treaments in the Kibwezi soil. However; plants in Kabete soil recorded shoot dry weight increases of 0 - 48%, 0 - 54%, 0 - 15.2% and 0 - 15.1% for the four tree species respectively. Correlation between nodule dry weight and shoot dry weight was significant at 5%- probability level for all the four tree species in the Kibwezi soil but was not significant in the Kabete soil. Correlation between shoot nitrogen content and shoot dry weight was significant at 5% probability level for c. calothyrsus and s. sesban in both the Kabete and Kibwezi soils.