E. Akyeampong¹ and Tekalign Mamo²International Livestock Centre for Africa (ILCA)
PO Box 5689, Addis Ababa, Ethiopia
1. Present address: International Council for Research in Agroforestry (ICRAF), Nairobi Kenya2. Present address: Agricultural Research Centre, Debre Zeit, Alemaya University of Agriculture, Ethiopia
Findings from a glasshouse study to assess the response of Sesbania sesban to N and P fertilization on two Ethiopian Vertisols are presented. S. sesban is an important multipurpose tree, tolerant to physical environmental stresses, with great potential in tropical highlands Two rates of N application, 0 and 100 kg ha-1, were used. The rates of P application were 0, 40, 80, 120, 160 and 200 kg ha-1. Soils used were from ILCA experimental fields at Shola (Addis Ababa) and Debre Zeit.
Nitrogen fertilization enhanced dry weights of leaves, stems and roots (thus total biomass). Response to P fertilization was dependent upon soil type and the presence of N. On the Debre Zeit soil, without N there was virtually no response; on the Shola soil, there was a linear increase in dry weight with increasing P. When N was supplied, maximum dry weight yields on both soils were achieved at 120 kg P ha-1, but declined at higher P rates. Improved plant weights as a result of N and P fertilization were generally greater on the Debre Zeit soil than on the Shola soil.
Soil analysis after cropping showed that soil available P increased with P application rates. Addition of N enhanced the uptake of P from the soils, especially the Shola soil. Soil available P decreased with length of growing period.
