Inoculation and phosphorus effects on Desmodium intortum and Sesbania sesban in the Ethiopian highlands

Field experiments were conducted to study the effects of inoculation and application of P on the productivity of Desmodium intortum on an Ultisol and Sesbania sesban on a Vertisol, Alfisol and Ultisol in the Ethiopian highlands. On the Vertisol, the effect of drainage by using broad-bed-and-furrow technology was also investigated. In desmodium, inoculation had no significant effect (P > 0.05) on nodule weight, but application of P was found to be necessary for nodulation as plants did not nodulate without P fertilizer. Both inoculation and P significantly increased plant DM and N yields. Inoculation had no significant effect on nodulation, plant DM or N yields of sesbania in any soil. Probably because of previous P applications, P had no significant effect on sesbania plants grown on the Vertisol. On the Alfisol and Ultisol, sesbania responded differently to P applied in the nursery or field. On the Alfisol, P applied in the nursery increased nodule, root and shoot DM and root and shoot N yields, but P applied in the field increased only nodule DM. The reverse occurred on an Ultisol, where P applied in the nursery had no effect on sesbania, but P applied in the field increased nodule, root and shoot DM, root N yield, and root and shoot P yields. Drainage of the Vertisol increased shoot DM and N yields. It is apparent that P deficiency is an important limiting factor to the use of inoculation technology to increase legume productivity in the Ethiopian highlands.